Review ArticleThe Review of GRACE Data Applications in TerrestrialHydrology Monitoring

Dong Jiang1 Jianhua Wang2 Yaohuan Huang1

Kang Zhou3 Xiangyi Ding2 and Jingying Fu1

1 Institute of Geographical Sciences and Natural Resources Research Chinese Academy of Sciences Beijing 100101 China2 State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin Department of Water ResourcesChina Institute of Hydropower ampWater Resources Research Beijing 100038 China

3 Computer Network Information Center Chinese Academy of Sciences Beijing 100190 China

Correspondence should be addressed to Jianhua Wang wjhiwhrcom and Yaohuan Huang huangyhlreisaccn

Received 14 February 2014 Revised 13 May 2014 Accepted 20 May 2014 Published 5 June 2014

Academic Editor Dawei Han

Copyright copy 2014 Dong Jiang et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The Gravity Recovery and Climate Experiment (GRACE) satellite provides a newmethod for terrestrial hydrology research whichcan be used for improving the monitoring result of the spatial and temporal changes of water cycle at large scale quickly The paperpresents a review of recent applications of GRACE data in terrestrial hydrology monitoring Firstly the scientific GRACE datasetis briefly introduced Recently main applications of GRACE data in terrestrial hydrological monitoring at large scale includingterrestrial water storage change evaluation hydrological components of groundwater and evapotranspiration (ET) retrievingdroughts analysis and glacier response of global change are described Both advantages and limitations ofGRACEdata applicationsare then discussed Recommendations for further research of the terrestrial water monitoring based on GRACE data are alsoproposed

1 Introduction

Intensified impact of human activities and global changeinevitably lead to the changes in the water cycle includingthe spatial and temporal distribution and the total amountof water resources [1 2] Terrestrial hydrology which isan important indicator in global change affects the globalclimate system in energy water and biogeochemical [3] Tra-ditional monitoring of terrestrial hydrology mainly dependson site measurements or model simulations which is costlyand time-consuming Furthermore for the scale effects ofthe conversion from observation points to large regionadditional error will be brought into spatially continuous dataobtained by statistical interpolation methods The accuracyof interpolation results may significantly decrease in areas faraway from observation sites Hydrological models and landsurface models solve the problem of simulation of terrestrialhydrology on the plane scale to some degree Howeverthe lack of systematic global fine-scale hydrological data

increases the model uncertainty and lowers the simulationaccuracy This restricts the practical application of hydro-logical models and land surface models in the monitoringof terrestrial hydrology With the rapid development ofremote sensing technology remote sensing holds significantpotential to the regional hydrological researches By offeringa useful and cost-effective approach to rapidly monitor ter-restrial hydrological parameters remote sensing technologyhas been widely used in hydrology Recently combinationmodels of remote sensing technology observation networkand hydrological models have been common in terrestrialhydrology studies However imaging satellite techniques andsatellite altimetry can only be used in the monitoring ofsurface water that represents just one component of totalwater storage They can be hardly applied in the monitoringof other components of terrestrial water such as soil water andgroundwater which impeded further applications of thesetechnologies in terrestrial hydrology

Hindawi Publishing CorporationAdvances in MeteorologyVolume 2014 Article ID 725131 9 pageshttpdxdoiorg1011552014725131

2 Advances in Meteorology

Launched in March 2002 the Gravity Recovery andClimate Experiment (GRACE) can provide an operationalproduct in the form of global gravity fields everysim30 days [4]After several gravity effects have been released (eg atmo-sphericmass variations and ocean tides) precise observationsof the time-series global gravity field changesmake the spatialmonitoring of water storage changes at large scale such asbasins possible Through 10 years of development GRACEsatellite data processing and corresponding TWS retrievalalgorithms are improved continuouslyThey are able to detectthe changes of TWS within the accuracy of 15 cm on a widerange of spatial scales and seasonal time scales [5] Comparedto imagery remote sensing methods they provide alternativetechnical methods for the estimation of glaciers surfacesnow soil water surface water groundwater evaporationand other components in the terrestrial hydrological systemIt provides a new technique for the large-scale monitoringof terrestrial water cycle The objective of this paper is topresent an overview ofGRACEdata applications in terrestrialhydrology monitoring including GRACE data processingmethods and TWS change retrieval and their application interrestrial hydrology and related fields

2 GRACE Data

GRACEgravity satellite programwas jointly developed by theNational Aeronautics and Space Administration (NASA) ofthe United States and the German Aerospace Center (DLR)with the objective of providing spatiotemporal variationsof the Earthrsquos gravity field The GRACE satellite programcan be also used to detect the atmosphere and ionosphereenvironment The US Jet Propulsion Laboratory (JPL) isresponsible for the project management of the GRACEgravity satellite program Monthly gravity field solutions arecomputed at the University of Texas at Austin Center forSpace Research (CSR) the German Research Centre forGeosciences Potsdam (GFZ) JPL Groupe de Recherche deGeodesie Spatiale (GRGS) and the Delft Institute of EarthObservation and Space Systems (DEOS) as well as DelftUniversity of Technology among others [4 6ndash8] GRACEutilizes a state-of-the-art technique to trace the spatiotempo-ral gravity field with an increased sensitivity by tracking themicrometer-precise intersatellite range and range-rate obser-vations between two coplanar low altitude (300 kmsim500 km)satellites and the distance between which is about 220 kmTo precisely measure the distance changes between twosatellites at micron meter level accuracy a K-band ranging(KBR) system based on carrier phase measurements in the K(26GHz) and Ka (32GHz) frequencies is provided Besidesfour key instrumentations of a GPS receiver (space-proofedmultichannel two-frequency) capacitive accelerometer laserretroreflector (LRR) and star camera are equipped on boardof each GRACE satellite [4 7]

By analyzing the relationship between orbits and forces ofGRACE satellites the Earthrsquos gravity field variety is estimatedbased on the dynamic equations of satellites motion Itmonitors the time-varying characteristics of long-wavelengthgravity field on a 15sim30-day or longer time scale Large-scale

mass redistribution (mass distribution changes over time) inthe Earth system reflects the interaction between substancesof various forms in the Earthrsquos internal system (atmosphereoceans and solid crust viscous mantle liquid outer coreand solid inner core) which are the important subjects ofEarth sciences Compared to the average Earthrsquos gravity fieldthe time-varying quantity of the gravity field is very smallbut it contains important geophysical information It revealsthe movement distribution and changes of all substancesin the Earth system and reflects the interaction between theatmosphere terrestrial water oceans and the solid Earth [6]

The time variation of global gravity field caused by theinfluence of solid Earth (including the inner core and theouter core) is mainly manifested on a 10-year or a longer timescale However temporal variation of gravity ismainly causedby the redistribution influence of atmosphere oceans andwater storages in the surface fluid envelopes of the earth on aseasonal or interannual time scale [9 10] The gravity effectsof tides (solid Earth oceans and atmosphere) and nontidal(atmosphere and oceans) are reduced in the data processingof GRACE gravity field model Therefore by excludingthe errors in gravity field model and the atmosphere andoceans models GRACE time-varying gravity field reflectsthe nonatmospheric and nonocean mass variations due towater mass variations on the continental area On a seasonalor shorter time scale it provides information on changes interrestrial water storage in large river basin [11]

3 Hydrological Applications

31 TWS Changes Monitoring The TWS is the most directhydrological parameter obtained by GRACEmonitoring Forthe main goal of GRACE satellite is to monitor the Earthrsquosgravity field variations early researches are focused on thefeasibility and accuracy of TWS retrieval from GRACE dataWahr et al [11] pointed out that the GRACE-based TWSretrieval required the consideration of the impacts fromshort-wave noises and leakage errors and the TWS retrievalresult is valid for large-scale river basins Further research ofRodell and Famiglietti showed that TWS accuracy could beimproved by increasing themonitoring temporal interval andspatial resolution of the monitored area [12 13] For regionslarger than 200000 km2 the TWS changes with intervals onmonth and longer time scale can be monitored and theaccuracy can reach 15 cm and above

The application of GRACE-based TWS changes datais mainly based on the combination of hydrological mod-els and land surface models GRACE-based TWS retrievalresults offer spatial and temporal distribution of verticallyintegrated water storage (surface water soil groundwaterand snowpack) in large river basins So the errors due tothe use of indirect indicators such as the flow rate andprecipitation in some hydrological models can be reduced Ininitial researches the GRACE-based TWS is only consideredas a reference to the simulation results from hydrologicalmodels (such as GDLAS and CPC) which does not involvethe uncertainty of hydrological models in the simulationprocess Hu et al [10] proposed that water storage changes in

Advances in Meteorology 3

Yangtze River could reach a magnitude of 34 cm equivalentwater height with the maximum occurring in the springand early autumn Using 5-year GRACE-based TWS changedata in China Zhong et al [14] pointed out that the waterstorage in the north-central region of China diminished at anannual rate of 24 cm water equivalent height By combiningGRACE and GPS network observation data Wang et al [15]achieved precise retrieval of TWS change in Nordic regionand North America Their studies showed that over the pastdecade a sharp increase appeared in the water storage inNorthAmerica and Scandinavia and awater recovery processis underway

With further study GRACE data is now considered asan important parameter to assess and improve hydrologicalmodel simulation Swenson andMilly [16] and Syed et al [17]used GRACE data to verify and improve TWS simulation offive climate models and the Global Land Data AssimilationSystem (GLDAS) respectively Niu and Yang [18] and Ngo-Duc et al [19] used GRACE data for the result verifica-tion of common land surface model (CLM) of NCAR andORCHIDEE and corrected the CLM by applying GRACE-based TWS changes data

Various quantitative analyses between hydrological mod-els and GRACE-based TWS showed that the two simu-lation results of large areas are in good consistency ona seasonal or longer time scale [16 20 21] Time-seriesanalyses of South and North America Southeast Asia theGanges River Basin Africa Eurasia and other large-scaleregions all showed that GRACE-based TWS reflected asignificant seasonal variation However given the limitationsin the spatial resolution of GRACE data the consistencyof hydrological models and GRACE data in smaller areasis not satisfactory [22] Excluding the errors of GRACE-based TWS change retrieval the inconsistency is mainly dueto the simulation errors of various TWS components fromhydrological models For example the generalized deviationin estimating the important elements such as groundwatersurface water and soil water storage by using hydrologicalmodels resulted in smaller magnitudes in TWS changes Theerrors in the simulation of rainfall convergence and otherhydrological processes generated phase deviation in TWSchanges time series [17 23 24] In addition by combinationof the measured data of rainfall recharge soil water andgroundwater GRACE-based TWSwas used for water storagevariation of basin on interannual annual seasonal andmonthly time scales [25 26]

32 Hydrological Components Evaluation With the improve-ment of GRACE-based TWS change accuracy the GRACEdata is further used in hydrology and water resourcesresearch For specific areas TWS changes can be expressedas [10]

119889119882

119889119905

= 119875 minus 119864 minus 119877 (1)

where 119889119882119889119905 represents TWS changes and the correspond-ing equivalent water height can be obtained from GRACE119875 represents precipitation 119864 represents evapotranspiration

and119877 represents surface runoff By combiningGRACE-basedTWS changes hydrological models and the measured datathe water storage components including groundwater soilwater ET and 119875 minus 119864 can be estimated respectively

Groundwater estimation is difficult in remote sensingapplications in hydrology Optical remote sensing methodscan only combine measured data with spectral data toconstruct an empirical model for the estimation of ground-water changes whose groundwater retrieval accuracy is poorConsidering the contribution of groundwater changes toTWS variation groundwater remote sensing using GRACEwas feasible by combination with ancillary measurements ofsurface waters and soil moisture Rodell and Famiglietti [27]firstly used GRACE-based TWS change data soil water andother auxiliary data to analyze the possibility of monitoringgroundwater changes Swenson et al [25] studied the relationbetween measured value of groundwater plus soil water andGRACE-based TWS changes and presented the possibilityand sources of error in groundwater estimation based onGRACE data on multiple time scales Strassberg et al [28]compared the spatiotemporal correlation between GRACE-based TWS changes and hydrological model simulationsand field monitoring data and proposed the uncertainty ofGRACE-based groundwater retrieval The above studies sug-gest that for aquifers larger than 450000 km2 the accuracyof GRACE-based groundwater can reach 87mm Rodellet al applied GRACE data to the groundwater subsidencemonitoring in India and found that excessive irrigation andhuman activities caused the groundwater in the northwestprovinces of India to decline at an annual rate of 30 cmsim40 cm [29]

Evapotranspiration (ET) is an important process param-eter to studies of hydrology which is difficult to measure at aregional or continental scale Although ET can be indirectlyestimated using remote sensing data based on empiricalmod-els energy balancemodels or physicalmodels (eg Penman-Monteith equation) recent remote-sensed ET estimation isfar from satisfactory [30] For ET is a complex process thatrelated to many variables its estimation uncertainty basedon remote sensing data brings errors to ET retrieval resultsBased on terrestrial water balance at scale of river basinchanges of regional ET can be estimated by combining TWSchange from GRACE with observed precipitation (119875) andrunoff data (119877) Rodell et al [31] first used the measuredprecipitation and runoff data to verify the feasibility ofGRACE-based ET retrieval However the overdependenceon measured data restricts the applicability of this methodTherefore Ramillien et al [32] improved this algorithm byusing the simulated runoff data from hydrological modelThe time-series analysis showed that the ET estimation andWGHM simulation were in good consistency Howeveruncertainty of GRACE-based ET estimation increases for itsoverdependence on accuracy of hydrological model simu-lated variables such as runoff In addition Swenson andWahr[33] combined GRACE-based TWS changes together withthe measured runoff data to estimate the difference betweenprecipitation and evapotranspiration (119875 minus 119864) By comparingwith 119875 minus 119864 results of a land surface model (GLDAS-Noah)

4 Advances in Meteorology

they found that the errors of GLDAS-Noah estimation aremainly due to model force parameter of precipitation

33 Drought Analysis Based on time-series analysis ofGRACE-based TWS change with high temporal resolu-tion extreme hydrological disasters can be monitored andalarmed Droughts for regional and time-series water storagedeficit are the most serious natural hazards that can lead tocrop losses and economic havoc in many areas For droughtscan be regarded as terrestrial water storage (TWS) changesthat are related to integrated bulk variables analysis relyingupon subcomponents (eg precipitation) or proxies (egNDVI and CWSI) of TWS is insufficient Herewith anotherhydrological application of GRACE is severe droughts anal-ysis Combined with the measurements and hydrologicalmodel simulations Leblanc et al [34] used GRACE datato detect droughts in Southeastern Australia between 2001and 2008 Based on time-series analysis of TWS changes insummers from 2002 to 2007 2005 extreme drought eventin the Amazon river basin was detected [35] which wasregarded as the worst in over a century GRACE data is moresensitive to droughts than data-assimilating climate and landsurface models such as NECEP and GLDAS which demon-strated the unique potential of GRACE in monitoring large-scale severe drought events Validated by two independenthydrological estimates of GLDAS and ECMWF and directgravity observations from superconducting gravimeters the2003 excess terrestrial water storage depletion was observedfrom GRACE which can be related to the record-breakingheat wave that occurred in central Europe in 2003 [36]It indicated that GRACE data can be used in heat wavedisaster monitoring and evaluation whose essence is heatwave caused droughts analysis Combining with imageryremote sensing methods Frappart and Wilson et al appliedGRACE data to flood monitoring in several flood zones suchas the Mekong River Basin and the Amazon River Basin[37 38] However compared to droughts the water storagechanges based on GRACE data of extreme floods are lessresponsive which will bring more uncertainty in GRACE-based floods analysis [39]

34 Glacier Mass Balance Detection Driven by global changeand population pressure accelerating of glaciers meltingand sea level rise has been a serious global ecologicalproblem GRACE time-variable gravity field enabled directmeasurement of mass loss rates of both mountain glacierand polar glacier systems As noted by Wouters et al theGRACE solutions can be used to allow regional estimationof trends though assessing the mass loss to be dominated bysummer events rather than by a linear trend [40] GRACE-based glacier mass melting volume and rate estimation ofAntarctic and Greenland indicate that accelerating polarglacier melting contributes greatly to the current eustatic sealevel rise [41ndash43] Gardner et al have also found a rapidlyincreasing mass loss in the Canadian Arctic Archipelago(CAA) for the period 2004ndash2009 [44] Ice loss rate estimationon glaciers of Asia Alaska and other global mountains basedon GRACE data also agrees with the global tendency of

accelerating glacial loss Accelerated melting of mountainglaciers worldwide might be contributing to the global sealevel rise by 073 plusmn 010mmyr [45 46] Moreover GRACE-based TWS change can be used for researches of differentclimate variability impact [47 48] whereas for the postglacialrebound effects and unique set of gravity data GRACEmission provided ice sheet mass change estimation includeslarge uncertainties [49] Mass change rates estimated by dif-ferent GRACE solutions may vary by a factor of two or moreSo the glacier mass balance detection needs considerableprocessing to yield usable mass change data [49]

4 Discussion and Conclusions

Through ten years of development GRACE data has beenwidely applied in terrestrial hydrology monitoring Gravitysatellite provides newdata sets for hydrology researches basedon remote sensing technology Compared with other kindsof hydrological schemes GRACE can provide realistic spa-tiotemporal variations of vertically integrated measurementof water storage (groundwater soil moisture surface watersnow water vegetation water etc) at the precision of tens ofmm of equivalent water height at large scale However thehydrologicalmonitoring based onGRACEdata needs furtherresearch for example retrieval accuracy improvement morequantitative analyses rather than qualitative analyses and soforthThe focus of future development includes the followingaspects

(1) Improving the Accuracy of Gravity Satellite MeasurementsBecause of the limitations of GRACE satellite sensors inorbital altitude vertical gravity gradient measurements highfrequency signal aliasing and accuratemeasurement of time-varying gravity signals the accuracy and spatial resolutionof time-varying Earth gravity field signals at medium andlong wavelength of GRACE is low which reduced the TWSchange retrieval accuracy Therefore the development of keytechnology in gravity satellite sensors to improve accuracyand spatial resolution of satellite monitored gravity field isthe basis for a wider application in terrestrial hydrologymonitoring

(2) Water Storage Retrieval Models Research Recently theappropriate spatial resolution forGRACE-basedTWS changeis 400 km and the data accuracy is generally 15 cm Limitedby recent constraints of GRACE satellite improvement ofretrieval models is the only method for spatial resolutionand accuracy retrieval of TWS increases For example it isfeasible to improve TWS accuracy by the atmosphere andocean models improvement in data preprocessing reducingthe gravity field changes noises caused by factors unrelated toterrestrial water such as tides and circulation of atmosphereand ocean In addition by applying different filtering meth-ods such as anisotropicGaussian filtering and spherical radialbasis function filtering wavelet analysis in different researchareas can also improve the spatial resolution and accuracyof TWS retrieval Water storage retrieval techniques involvevarious aspects (eg GRACEdata preprocessing gravity fieldretrieval and TWS changes estimation) of the conversion

Advances in Meteorology 5

of GRACE gravity field data to TWS changes which are allimportant in TWS retrieval improvement

(3) Further Combination of GRACE Data with Associ-ated Hydrological Models For GRACE-based TWS changesretrieval does not involve the hydrological mechanisms it isnecessary to complement GRACE-based TWS by hydrologi-cal models for furthering its application in terrestrial hydrol-ogy monitoring Further combination of GRACE and hydro-logical models needs resolving their consistencies of spacetime and component Spatial consistency can be solvedby adjusting the calculation unit of hydrological models toreflect the spatial variability (such as distributed hydrologicalmodels) Temporal consistency requires analysis of upscalingGRACE data and downscaling hydrological models simula-tion Component consistency can be achieved by GRACE-based TWS signals subdivision or revising parameters ofhydrological models to TWS Through space time andcomponent consistency improvement the gravity field dataandmeasured data together can become basic dataset to forcehydrological models in the future

Appendices

A Water Storage Change Retrieval

Thechanges in terrestrial water storage result inmass redistri-bution in the Earthrsquos system thereby causing changes in thegravity field For a fixed continental region the changes inwater storage (including soil water and surface snow) comefrom rainfall evapotranspiration river transportation anddeep underground infiltration Except the rainfall which cancause increased water storage the remaining three processesall reduce it [10] Using the FG5 absolute gravimeter Zhanget al [50] measured the gravity change of nearly 10minus7msdotsminus2 attheWuhanUniversity site before and after a rainstorm whichclearly shows the influence of terrestrial water variation ongravity The Earthrsquos gravity field can be expressed as geoid

119873(120579 120582)

= 119886

infin

sum

119899=0

119899

sum

119898=0

[119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A1)

where 119899 and 119898 are harmonic degree and order of the gravityfield respectively 119886 is the Earthrsquos equatorial radius (about6371 km) 120579 and 120582 are colatitudes (the difference between90∘ and latitude) and longitude 119862

119899119898and 119878

119899119898are spherical

harmonic coefficients (dimensionless)119875119899119898

is the normalizedassociated Legendre functions The maximum value 119873 ofthe order 119899 of ideal gravity field should be infinite (119873 sim

infin) while the actual order of spherical harmonic coefficientsobtained by the gravity satellite has a finite value (119873 lt infin)and the spatial resolution of gravity field data is estimatedapproximately to be 120587119886119873 [51] Geoid height changes Δ119873

caused by the movement of substances on the Earthrsquos surfacecan be expressed as

Δ119873 (120579 120582)

= 119886

infin

sum

119899=0

119899

sum

119898=0

[Δ119862

119899119898cos (119898120582) + Δ119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A2)

where Δ119862119899119898

and Δ119878119899119898

are the changes of 119899-degree 119898-orderspherical harmonic coefficients of geoid and can be expressedas [5 52]

Δ119862

119899119898

Δ119878

119899119898

=

3

4120587119886120588

119886(2119899 + 1)

timesintΔ120588 (119903 120579 120582) 119875

119899119898(cos 120579)( 119903

119886

)

119899+2

cos (119898120582)sin (119898120582) sin 120579119889120579 119889120582 119889119903

(A3)

where 120588119886is the average density of the Earth (5517 kgm3)

and Δ120588(119903 120579 120582) is the change of bulk density at a particularlocation In gravity field inversion because the height changeof substances on the Earthrsquos surface 119867 is relatively smallcompared to the Earthrsquos average radius 119886 in gravity fieldretrieval ((119903119886) asymp 1) the changes of the gravity field directlycaused by the surface mass can be expressed as

Δ119862

119899119898

Δ119878

119899119898

surf

=

3

4120587119886120588

119886(2119899 + 1)

times intΔ120590 (120579 120582) 119875

119899119898(cos 120579) cos (119898120582)sin (119898120582) sin 120579119889120579 119889120582

(A4)

where Δ120590 is surface density change Δ120590 = intΔ120588(119903 120579 120582)119889119903Furthermore the surface mass variation in loads will causedeformation to the solid Earth which in turn can indirectlycause variations to the gravity field This can be expressed as[5 52]

Δ119862

119899119898

Δ119878

119899119898

soild

=

3119896

1015840

119899

4120587119886120588

119886(2119899 + 1)

times intΔ120590 (120579 120582) 119875

119899119898(cos 120579) cos (119898120582)sin (119898120582) sin 120579119889120579 119889120582

(A5)

where 119896

1015840

119899is load LOVE number of coefficients and the

specific value of 1198961015840119899can be found in relevant literature [11]

6 Advances in Meteorology

Thus the change of the Earthrsquos gravity field caused by massvariations on the Earthrsquos surface is given by

Δ119862

119899119898

Δ119878

119899119898

=

Δ119862

119899119898

Δ119878

119899119898

surf

+

Δ119862

119899119898

Δ119878

119899119898

soild

= (1 + 119896

1015840

119899)

Δ119862

119899119898

Δ119878

119899119898

surf

(A6)

If the spherical harmonic expansion is performed on thesurface density change Δ120590 then

Δ120590 (120579 120582)

= 119886120588

119908

infin

sum

119899=0

119899

sum

119898=0

[

119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A7)

where 120588119908is the density of water andΔ120590120588

119908can be considered

as mass variation on the Earthrsquos surface expressed in waterequivalent height Wahr et al [5] proposed that

Δ

119862

119899119898

Δ

119878

119899119898

=

120588

119886

3120588

119908

2119899 + 1

1 + 119896

1015840

119899

Δ119862

119899119898

Δ119878

119899119898

(A8)

The surface density changeΔ120590 can be calculated using thefollowing equation

Δ120590 (120579 120582)

=

119886120588

119886

3

infin

sum

119899=0

119899

sum

119898=0

2119899 + 1

1 + 119896

1015840

119899

[119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)]

times 119875

119899119898(cos 120579)

(A9)

For ocean and atmosphere mass variations are removedbased on Parallel Ocean Program (POP) model the aboveequation is the basic equation for the retrieval of surfacemassvariations based on spatiotemporal changes gravity fieldThe Earthrsquos surface density changes can be derived from thechanges of gravity field coefficients obtained from GRACEsatellites

B Evaluation Errors

Currently the latest available GRACE dataset product is theRL05 The accuracy of data provided by CSR and GFZ isbetter than that provided by JPL The evaluation errors ofGRACE are brought from satellite instrumentsmeasurementretrieval models and other factors as follows

(1) Gravity field data measured by GRACE satellite maybe contaminated by satellite measurement errors forthe influence of satellite orbit satellite K-band rang-ing and accelerometer measurement [20] The satel-lite measurement errors also include poor accuracyof C20 due to the insensitivity of track geometry to

the gravity fieldrsquos low degree gravitational variations[5 20] It is generally releasedwith removing variationof C20 [10] or replacing it by satellite laser ranging(SLR) substitution [20] In addition the missing offirst-degree spherical harmonic coefficients will alsobring error to GRACE It can commonly be resolvedby substituting value calculated from the term of theseasonal changes of the Earthrsquos mass center [53 54] orignoring its impact [55]

(2) In theory the retrieval of gravity field variation needsto use spherical harmonic coefficients of all degreesfrom 0 to infinity However gravity satellites can onlyprovide definite order data So the surface densitychange Δ120590 in retrieval models is treated by sphericalharmonic expansion to definite orders For the impactof high-order terms on the Earthrsquos surface densitychange Δ120590 cannot be ignored it results in truncationerrors in gravity field retrieval RL05 water storagedata is estimated by CSR using a retrieval modeltruncated to degree 60 [8] Zhu et al (2008) comparedthe global water storage retrieval results using modelstruncated to 15 degrees 20 degrees 35 degrees and60 degrees [56]They found that although some infor-mation of TWS change may be missing the retrievalresult of TWS change became more marked withlower truncation degree Generally the water storageretrieval truncated to order 60 is widely adopted [17]

(3) For terrestrial water monitoring focusing on themass changes of a particular area (eg river basin)it requires the integral process on density changeΔ120590 = ((intΔ120590(120579 120582)119906(120579 120582)119889Ω)Ω) The function ofregional characteristics 119906(120579 120582) is equal to 1 insidethe particular area and to zero outside The errorwill be brought for the discontinuity of 119906(120579 120582) in thedomain of integration In addition for the influenceof rapid increase of the errors of GRACE gravityfield model coefficients with increase of sphericalharmonic coefficients degree signal leakage errorsand the striping pollution [23] filtering methods areproposed to smooth GRACE data for noise reducingwhich will result in filtering errors of retrieval resultsProposed filtering methods include spatial averagingsymmetric Gaussian filtering optimized decorrela-tion filtering time-series method global hydrolog-ical model correction method kernel-independentcomponent analysis and optimal smoothing kernelmethod [53 57ndash62] Using filtering for the integraltreatment of surface density changes can effectivelyremove the striping to a certain extent Howeverthe obtained average surface density is critical for itreduces the useful energy of geophysical signals andresults in filtering errors In addition the existingfiltering methods require the support of a prioriknowledge (such as filtering radius and truncationdegree) Therefore in the actual retrieval process thefilter selection and parameter calibration require anunderstanding of the specific regional characteristics[60 63]

Advances in Meteorology 7

(4) TWS changes retrieval based on spatiotemporal vari-ations of gravity field remains considerable uncer-tainty which includes errors produced in the removalof tidal movement and the mass migration becauseof the atmosphere and ocean circulation [11] as wellas the errors in hydrological models used for theestimation of other terrestrial water parameters [6]

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project was supported by National Natural ScienceFoundation of China (Grant no 51309210) and the ChineseAcademy of Sciences (Grant no KZZD-EW-08)

References

[1] Y Huang D Jiang D Zhuang Y Zhu and J Fu ldquoAn improvedapproach for modeling spatial distribution of water use profitmdasha case study in Tuhai Majia Basin Chinardquo Ecological Indicatorsvol 36 pp 94ndash99 2014

[2] Y-H Huang D Jiang D-F Zhuang J-H Wang H-J Yangand H-Y Ren ldquoEvaluation of relative water use efficiency(RWUE) at a regional scale a case study of Tuhai-Majia BasinChinardquo Water Science and Technology vol 66 no 5 pp 927ndash933 2012

[3] J S Famiglietti ldquoRemote sensing of terrestrial water storagesoil moisture and surface watersrdquo in The State of the PlanetFrontiers and Challenges in Geophysics R S J Sparks and C JHawkesworth Eds pp 197ndash207 2004

[4] B D Tapley S Bettadpur M Watkins and C Reigber ldquoThegravity recovery and climate experiment mission overview andearly resultsrdquo Geophysical Research Letters vol 31 no 9 ArticleID L09607 2004

[5] J Wahr S Swenson V Zlotnicki and I Velicogna ldquoTime-variable gravity from GRACE first resultsrdquo GeophysicalResearch Letters vol 31 no 11 Article ID L11501 2004

[6] A Guntner ldquoImprovement of global hydrological models usingGRACE datardquo Surveys in Geophysics vol 29 no 4-5 pp 375ndash397 2008

[7] G Ramillien J S Famiglietti and J Wahr ldquoDetection ofcontinental hydrology and glaciology Signals from GRACE areviewrdquo Surveys inGeophysics vol 29 no 4-5 pp 361ndash374 2008

[8] D P Chambers ldquoConverting 11 Release-04 Gravity Coefficientsinto Maps of Equivalent Water Thicknessrdquo 2007 httpgrace-tellusjplnasagovfilesGRACE-dpc200711 RL04pdf

[9] M Becker W LLovel A Cazenave A Guntner and J-FCretaux ldquoRecent hydrological behavior of the East Africangreat lakes region inferred from GRACE satellite altimetry andrainfall observationsrdquo Comptes Rendus Geoscience vol 342 no3 pp 223ndash233 2010

[10] X Hu J Chen Y Zhou C Huang and X Liao ldquoSeasonal waterstorage change of the Yangtze River basin detected by GracerdquoScience in China D vol 49 no 5 pp 483ndash491 2006

[11] J Wahr M Molenaar and F Bryan ldquoTime variability ofthe Earths gravity field hydrological and oceanic effects and

their possible detection using GRACErdquo Journal of GeophysicalResearch B vol 103 no 12 pp 30205ndash30229 1998

[12] M Rodell and J S Famiglietti ldquoDetectability of variations incontinental water storage from satellite observations of the timedependent gravity fieldrdquo Water Resources Research vol 35 no9 pp 2705ndash2723 1999

[13] M Rodell and J S Famiglietti ldquoAn analysis of terrestrial waterstorage variations in Illinois with implications for the GravityRecovery and Climate Experiment (GRACE)rdquoWater ResourcesResearch vol 37 no 5 pp 1327ndash1339 2001

[14] M Zhong J Duan H Xu P Peng H Yan and Y ZhuldquoTrend of China land water storage redistribution at medi-and large-spatial scales in recent five years by satellite gravityobservationsrdquo Chinese Science Bulletin vol 54 no 5 pp 816ndash821 2009

[15] H Wang L Jia H Steffen et al ldquoIncreased water storage inNorth America and Scandinavia from GRACE gravity datardquoNature Geoscience vol 6 no 1 pp 38ndash42 2013

[16] S C Swenson and P C D Milly ldquoClimate model biases inseasonally of continental water storage revealed by satellitegravimetryrdquoWater Resources Research vol 42 no 3 Article IDW03201 2006

[17] T H Syed J S FamigliettiM Rodell J Chen andC RWilsonldquoAnalysis of terrestrial water storage changes from GRACE andGLDASrdquo Water Resources Research vol 44 no 2 Article IDW02433 2008

[18] G-Y Niu and Z-L Yang ldquoAssessing a land surface modelsimprovements with GRACE estimatesrdquo Geophysical ResearchLetters vol 33 no 7 Article ID L07401 2006

[19] T Ngo-Duc K Laval G Ramillien J Polcher and A CazenaveldquoValidation of the land water storage simulated by OrganisingCarbon and Hydrology in Dynamic Ecosystems (ORCHIDEE)with Gravity Recovery and Climate Experiment (GRACE)datardquo Water Resources Research vol 43 no 4 Article IDW04427 2007

[20] J L Chen C R Wilson B D Tapley and J C Ries ldquoLowdegree gravitational changes from GRACE validation andinterpretationrdquo Geophysical Research Letters vol 31 no 22Article ID L22607 pp 1ndash5 2004

[21] R Klees E A Revtova B C Gunter et al ldquoThe design of anoptimal filter for monthly GRACE gravity modelsrdquo GeophysicalJournal International vol 175 no 2 pp 417ndash432 2008

[22] K-W Seo C R Wilson J S Famiglietti J L Chen andM Rodell ldquoTerrestrial water mass load changes from GravityRecovery and Climate Experiment (GRACE)rdquoWater ResourcesResearch vol 42 no 5 Article ID W05417 2006

[23] B D Tapley S Bettadpur J C Ries P F Thompson and MM Watkins ldquoGRACE measurements of mass variability in theEarth systemrdquo Science vol 305 no 5683 pp 503ndash505 2004

[24] D P Lettenmaier and J S Famiglietti ldquoHydrology water fromon highrdquo Nature vol 444 no 7119 pp 562ndash563 2006

[25] S Swenson P J-F Yeh J Wahr and J Famiglietti ldquoA compari-son of terrestrial water storage variations from GRACE with insitu measurements from Illinoisrdquo Geophysical Research Lettersvol 33 no 16 Article ID L16401 2006

[26] L Xavier M Becker A Cazenave L Longuevergne W Lloveland O C R Filho ldquoInterannual variability in water storageover 2003ndash2008 in the Amazon Basin from GRACE spacegravimetry in situ river level and precipitation datardquo RemoteSensing of Environment vol 114 no 8 pp 1629ndash1637 2010

8 Advances in Meteorology

[27] M Rodell and J S Famiglietti ldquoThe potential for satellite-basedmonitoring of groundwater storage changes using GRACE theHigh Plains aquifer Central USrdquo Journal of Hydrology vol 263no 1ndash4 pp 245ndash256 2002

[28] G Strassberg B R Scanlon and M Rodell ldquoComparison ofseasonal terrestrial water storage variations from GRACE withgroundwater-level measurements from the High Plains Aquifer(USA)rdquo Geophysical Research Letters vol 34 no 14 Article IDL14402 2007

[29] M Rodell I Velicogna and J S Famiglietti ldquoSatellite-basedestimates of groundwater depletion in Indiardquo Nature vol 460no 7258 pp 999ndash1002 2009

[30] X Lu and Q Zhuang ldquoEvaluating evapotranspiration andwater-use efficiency of terrestrial ecosystems in the contermi-nous United States using MODIS and AmeriFlux datardquo RemoteSensing of Environment vol 114 no 9 pp 1924ndash1939 2010

[31] M Rodell J S Famiglietti J Chen et al ldquoBasin scale estimatesof evapotranspiration using GRACE and other observationsrdquoGeophysical Research Letters vol 31 no 20 Article ID L205042004

[32] G Ramillien F Frappart AGuntner TNgo-DucA Cazenaveand K Laval ldquoTime variations of the regional evapotranspi-ration rate from Gravity Recovery and Climate Experiment(GRACE) satellite gravimetryrdquo Water Resources Research vol42 no 10 Article ID W10403 2006

[33] S Swenson and J Wahr ldquoEstimating large-scale precipitationminus evapotranspiration from GRACE satellite gravity mea-surementsrdquo Journal of Hydrometeorology vol 7 no 2 pp 252ndash270 2006

[34] M Leblanc P Tregoning G Ramillien S O Tweed andA Fakes ldquoBasin-scale integrated observations of the early21st century multiyear drought in southeast Australiardquo WaterResources Research vol 45 no 4 Article IDW04408 2009

[35] J L Chen C R Wilson B D Tapley Z L Yang and GY Niu ldquo2005 drought event in the Amazon River basin asmeasured byGRACE and estimated by climatemodelsrdquo Journalof Geophysical Research B vol 114 no 5 Article ID B054042009

[36] O B Andersen S I Seneviratne J Hinderer and P ViterboldquoGRACE-derived terrestrial water storage depletion associatedwith the 2003 European heat waverdquo Geophysical ResearchLetters vol 32 no 18 Article ID L18405 pp 1ndash4 2005

[37] F Frappart K Do Minh J LHermitte et al ldquoWater volumechange in the lower Mekong from satellite altimetry andimagery datardquo Geophysical Journal International vol 167 no 2pp 570ndash584 2006

[38] M D Wilson P Bates D Alsdorf et al ldquoModeling large-scale inundation of Amazonian seasonally flooded wetlandsrdquoGeophysical Research Letters vol 34 no 15 Article ID L154042007

[39] S-C Han C K Shum C Jekeli and D Alsdorf ldquoImprovedestimation of terrestrial water storage changes from GRACErdquoGeophysical Research Letters vol 32 no 7 Article ID L07302pp 1ndash5 2005

[40] B Wouters D Chambers and E J O Schrama ldquoGRACEobserves small-scale mass loss in Greenlandrdquo GeophysicalResearch Letters vol 35 no 20 Article ID L20501 2008

[41] I Velicogna and J Wahr ldquoMeasurements of time-variablegravity showmass loss in Antarcticardquo Science vol 311 no 5768pp 1754ndash1756 2006

[42] D C Slobbe P Ditmar and R C Lindenbergh ldquoEstimatingthe rates of mass change ice volume change and snow volume

change in Greenland from ICESat and GRACE datardquo Geophys-ical Journal International vol 176 no 1 pp 95ndash106 2009

[43] P L Svendsen O B Andersen and A A Nielsen ldquoAccelerationof the Greenland ice sheet mass loss as observed by GRACEconfidence and sensitivityrdquo Earth and Planetary Science Lettersvol 364 pp 24ndash29 2013

[44] A S Gardner G Moholdt B Wouters et al ldquoSharply increasedmass loss from glaciers and ice caps in the Canadian ArcticArchipelagordquo Nature vol 473 no 7347 pp 357ndash360 2011

[45] J L Chen B D Tapley and C R Wilson ldquoAlaskan mountainglacial melting observed by satellite gravimetryrdquo Earth andPlanetary Science Letters vol 248 no 1-2 pp 353ndash363 2006

[46] K Matsuo and K Heki ldquoTime-variable ice loss in Asianhigh mountains from satellite gravimetryrdquo Earth and PlanetaryScience Letters vol 290 no 1-2 pp 30ndash36 2010

[47] D Garcıa-Garcıa C C Ummenhofer and V Zlotnicki ldquoAus-tralian water mass variations fromGRACE data linked to Indo-Pacific climate variabilityrdquo Remote Sensing of Environment vol115 no 9 pp 2175ndash2183 2011

[48] W W Immerzeel L P H van Beek and M F P BierkensldquoClimate change will affect the asian water towersrdquo Science vol328 no 5984 pp 1382ndash1385 2010

[49] L S Soslashrensen S B Simonsen K Nielsen et al ldquoMass balanceof the Greenland ice sheet (2003ndash2008) from ICESat datamdashtheimpact of interpolation sampling and firn densityrdquo Cryospherevol 5 no 1 pp 173ndash186 2011

[50] W Zhang Y Wang and C Zhang ldquoThe preliminary analysisof effects of the soil moisture on gravity observationsrdquo Carto-graphica Sinica vol 30 no 2 pp 108ndash111 2001

[51] G Ramillien J S Famiglietti and J Wahr ldquoDetection ofcontinental hydrology and glaciology signals from GRACE areviewrdquo Surveys inGeophysics vol 29 no 4-5 pp 361ndash374 2008

[52] J L Chen C R Wilson R J Eanes and B D TapleyldquoGeophysical contributions to satellite nodal residual variationrdquoJournal of Geophysical Research B vol 104 no 10 pp 23237ndash23244 1999

[53] J K Willis D P Chambers and R S Nerem ldquoAssessing theglobally averaged sea level budget on seasonal to interannualtimescalesrdquo Journal of Geophysical Research C vol 113 no 6Article ID C06015 2008

[54] E W Leuliette and L Miller ldquoClosing the sea level rise budgetwith altimetry Argo and Gracerdquo Geophysical Research Lettersvol 36 no 4 Article ID L04608 2009

[55] J L Chen C RWilson J S Famiglietti andMRodell ldquoAttenu-ation effect on seasonal basin-scale water storage changes fromGRACE time-variable gravityrdquo Journal of Geodesy vol 81 no 4pp 237ndash245 2007

[56] G Zhu J Li HWen and JWang ldquoStudy on variations of globalcontinental water storage with GRACE gravity field modelsrdquoJournal of Geodesy and Geodynamics vol 28 no 5 pp 39ndash442008

[57] S Swenson and J Wahr ldquoMethods for inferring regionalsurface-mass anomalies from Gravity Recovery and ClimateExperiment (GRACE) measurements of time-variable gravityrdquoJournal of Geophysical Research B vol 107 no 9 pp 3-1ndash3-132002

[58] S Swenson and J Wahr ldquoMonitoring changes in continentalwater storage with gracerdquo Space Science Reviews vol 108 no1-2 pp 345ndash354 2003

[59] K-W Seo and C RWilson ldquoSimulated estimation of hydrolog-ical loads fromGRACErdquo Journal of Geodesy vol 78 no 7-8 pp442ndash456 2005

Advances in Meteorology 9

[60] S Swenson and J Wahr ldquoPost-processing removal of correlatederrors in GRACE datardquoGeophysical Research Letters vol 33 no8 Article ID L08402 2006

[61] G Ramillien F Frappart A Cazenave and A Guntner ldquoTimevariations of land water storage from an inversion of 2 years ofGRACE geoidsrdquo Earth and Planetary Science Letters vol 235no 1-2 pp 283ndash301 2005

[62] F Frederic G Ramillien M Leblanc et al ldquoAn independentcomponent analysis filtering approach for estimating continen-tal hydrology in the GRACE gravity datardquo Remote Sensing ofEnvironment vol 115 no 1 pp 187ndash204 2011

[63] S Werth A Guntner R Schmidt and J Kusche ldquoEvaluation ofGRACE filter tools from a hydrological perspectiverdquo Geophysi-cal Journal International vol 179 no 3 pp 1499ndash1515 2009

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Applied ampEnvironmentalSoil Science

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Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

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MineralogyInternational Journal of

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Geological ResearchJournal of

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Geology Advances in

2 Advances in Meteorology

Launched in March 2002 the Gravity Recovery andClimate Experiment (GRACE) can provide an operationalproduct in the form of global gravity fields everysim30 days [4]After several gravity effects have been released (eg atmo-sphericmass variations and ocean tides) precise observationsof the time-series global gravity field changesmake the spatialmonitoring of water storage changes at large scale such asbasins possible Through 10 years of development GRACEsatellite data processing and corresponding TWS retrievalalgorithms are improved continuouslyThey are able to detectthe changes of TWS within the accuracy of 15 cm on a widerange of spatial scales and seasonal time scales [5] Comparedto imagery remote sensing methods they provide alternativetechnical methods for the estimation of glaciers surfacesnow soil water surface water groundwater evaporationand other components in the terrestrial hydrological systemIt provides a new technique for the large-scale monitoringof terrestrial water cycle The objective of this paper is topresent an overview ofGRACEdata applications in terrestrialhydrology monitoring including GRACE data processingmethods and TWS change retrieval and their application interrestrial hydrology and related fields

2 GRACE Data

GRACEgravity satellite programwas jointly developed by theNational Aeronautics and Space Administration (NASA) ofthe United States and the German Aerospace Center (DLR)with the objective of providing spatiotemporal variationsof the Earthrsquos gravity field The GRACE satellite programcan be also used to detect the atmosphere and ionosphereenvironment The US Jet Propulsion Laboratory (JPL) isresponsible for the project management of the GRACEgravity satellite program Monthly gravity field solutions arecomputed at the University of Texas at Austin Center forSpace Research (CSR) the German Research Centre forGeosciences Potsdam (GFZ) JPL Groupe de Recherche deGeodesie Spatiale (GRGS) and the Delft Institute of EarthObservation and Space Systems (DEOS) as well as DelftUniversity of Technology among others [4 6ndash8] GRACEutilizes a state-of-the-art technique to trace the spatiotempo-ral gravity field with an increased sensitivity by tracking themicrometer-precise intersatellite range and range-rate obser-vations between two coplanar low altitude (300 kmsim500 km)satellites and the distance between which is about 220 kmTo precisely measure the distance changes between twosatellites at micron meter level accuracy a K-band ranging(KBR) system based on carrier phase measurements in the K(26GHz) and Ka (32GHz) frequencies is provided Besidesfour key instrumentations of a GPS receiver (space-proofedmultichannel two-frequency) capacitive accelerometer laserretroreflector (LRR) and star camera are equipped on boardof each GRACE satellite [4 7]

By analyzing the relationship between orbits and forces ofGRACE satellites the Earthrsquos gravity field variety is estimatedbased on the dynamic equations of satellites motion Itmonitors the time-varying characteristics of long-wavelengthgravity field on a 15sim30-day or longer time scale Large-scale

mass redistribution (mass distribution changes over time) inthe Earth system reflects the interaction between substancesof various forms in the Earthrsquos internal system (atmosphereoceans and solid crust viscous mantle liquid outer coreand solid inner core) which are the important subjects ofEarth sciences Compared to the average Earthrsquos gravity fieldthe time-varying quantity of the gravity field is very smallbut it contains important geophysical information It revealsthe movement distribution and changes of all substancesin the Earth system and reflects the interaction between theatmosphere terrestrial water oceans and the solid Earth [6]

The time variation of global gravity field caused by theinfluence of solid Earth (including the inner core and theouter core) is mainly manifested on a 10-year or a longer timescale However temporal variation of gravity ismainly causedby the redistribution influence of atmosphere oceans andwater storages in the surface fluid envelopes of the earth on aseasonal or interannual time scale [9 10] The gravity effectsof tides (solid Earth oceans and atmosphere) and nontidal(atmosphere and oceans) are reduced in the data processingof GRACE gravity field model Therefore by excludingthe errors in gravity field model and the atmosphere andoceans models GRACE time-varying gravity field reflectsthe nonatmospheric and nonocean mass variations due towater mass variations on the continental area On a seasonalor shorter time scale it provides information on changes interrestrial water storage in large river basin [11]

3 Hydrological Applications

31 TWS Changes Monitoring The TWS is the most directhydrological parameter obtained by GRACEmonitoring Forthe main goal of GRACE satellite is to monitor the Earthrsquosgravity field variations early researches are focused on thefeasibility and accuracy of TWS retrieval from GRACE dataWahr et al [11] pointed out that the GRACE-based TWSretrieval required the consideration of the impacts fromshort-wave noises and leakage errors and the TWS retrievalresult is valid for large-scale river basins Further research ofRodell and Famiglietti showed that TWS accuracy could beimproved by increasing themonitoring temporal interval andspatial resolution of the monitored area [12 13] For regionslarger than 200000 km2 the TWS changes with intervals onmonth and longer time scale can be monitored and theaccuracy can reach 15 cm and above

The application of GRACE-based TWS changes datais mainly based on the combination of hydrological mod-els and land surface models GRACE-based TWS retrievalresults offer spatial and temporal distribution of verticallyintegrated water storage (surface water soil groundwaterand snowpack) in large river basins So the errors due tothe use of indirect indicators such as the flow rate andprecipitation in some hydrological models can be reduced Ininitial researches the GRACE-based TWS is only consideredas a reference to the simulation results from hydrologicalmodels (such as GDLAS and CPC) which does not involvethe uncertainty of hydrological models in the simulationprocess Hu et al [10] proposed that water storage changes in

Advances in Meteorology 3

Yangtze River could reach a magnitude of 34 cm equivalentwater height with the maximum occurring in the springand early autumn Using 5-year GRACE-based TWS changedata in China Zhong et al [14] pointed out that the waterstorage in the north-central region of China diminished at anannual rate of 24 cm water equivalent height By combiningGRACE and GPS network observation data Wang et al [15]achieved precise retrieval of TWS change in Nordic regionand North America Their studies showed that over the pastdecade a sharp increase appeared in the water storage inNorthAmerica and Scandinavia and awater recovery processis underway

With further study GRACE data is now considered asan important parameter to assess and improve hydrologicalmodel simulation Swenson andMilly [16] and Syed et al [17]used GRACE data to verify and improve TWS simulation offive climate models and the Global Land Data AssimilationSystem (GLDAS) respectively Niu and Yang [18] and Ngo-Duc et al [19] used GRACE data for the result verifica-tion of common land surface model (CLM) of NCAR andORCHIDEE and corrected the CLM by applying GRACE-based TWS changes data

Various quantitative analyses between hydrological mod-els and GRACE-based TWS showed that the two simu-lation results of large areas are in good consistency ona seasonal or longer time scale [16 20 21] Time-seriesanalyses of South and North America Southeast Asia theGanges River Basin Africa Eurasia and other large-scaleregions all showed that GRACE-based TWS reflected asignificant seasonal variation However given the limitationsin the spatial resolution of GRACE data the consistencyof hydrological models and GRACE data in smaller areasis not satisfactory [22] Excluding the errors of GRACE-based TWS change retrieval the inconsistency is mainly dueto the simulation errors of various TWS components fromhydrological models For example the generalized deviationin estimating the important elements such as groundwatersurface water and soil water storage by using hydrologicalmodels resulted in smaller magnitudes in TWS changes Theerrors in the simulation of rainfall convergence and otherhydrological processes generated phase deviation in TWSchanges time series [17 23 24] In addition by combinationof the measured data of rainfall recharge soil water andgroundwater GRACE-based TWSwas used for water storagevariation of basin on interannual annual seasonal andmonthly time scales [25 26]

32 Hydrological Components Evaluation With the improve-ment of GRACE-based TWS change accuracy the GRACEdata is further used in hydrology and water resourcesresearch For specific areas TWS changes can be expressedas [10]

119889119882

119889119905

= 119875 minus 119864 minus 119877 (1)

where 119889119882119889119905 represents TWS changes and the correspond-ing equivalent water height can be obtained from GRACE119875 represents precipitation 119864 represents evapotranspiration

and119877 represents surface runoff By combiningGRACE-basedTWS changes hydrological models and the measured datathe water storage components including groundwater soilwater ET and 119875 minus 119864 can be estimated respectively

Groundwater estimation is difficult in remote sensingapplications in hydrology Optical remote sensing methodscan only combine measured data with spectral data toconstruct an empirical model for the estimation of ground-water changes whose groundwater retrieval accuracy is poorConsidering the contribution of groundwater changes toTWS variation groundwater remote sensing using GRACEwas feasible by combination with ancillary measurements ofsurface waters and soil moisture Rodell and Famiglietti [27]firstly used GRACE-based TWS change data soil water andother auxiliary data to analyze the possibility of monitoringgroundwater changes Swenson et al [25] studied the relationbetween measured value of groundwater plus soil water andGRACE-based TWS changes and presented the possibilityand sources of error in groundwater estimation based onGRACE data on multiple time scales Strassberg et al [28]compared the spatiotemporal correlation between GRACE-based TWS changes and hydrological model simulationsand field monitoring data and proposed the uncertainty ofGRACE-based groundwater retrieval The above studies sug-gest that for aquifers larger than 450000 km2 the accuracyof GRACE-based groundwater can reach 87mm Rodellet al applied GRACE data to the groundwater subsidencemonitoring in India and found that excessive irrigation andhuman activities caused the groundwater in the northwestprovinces of India to decline at an annual rate of 30 cmsim40 cm [29]

Evapotranspiration (ET) is an important process param-eter to studies of hydrology which is difficult to measure at aregional or continental scale Although ET can be indirectlyestimated using remote sensing data based on empiricalmod-els energy balancemodels or physicalmodels (eg Penman-Monteith equation) recent remote-sensed ET estimation isfar from satisfactory [30] For ET is a complex process thatrelated to many variables its estimation uncertainty basedon remote sensing data brings errors to ET retrieval resultsBased on terrestrial water balance at scale of river basinchanges of regional ET can be estimated by combining TWSchange from GRACE with observed precipitation (119875) andrunoff data (119877) Rodell et al [31] first used the measuredprecipitation and runoff data to verify the feasibility ofGRACE-based ET retrieval However the overdependenceon measured data restricts the applicability of this methodTherefore Ramillien et al [32] improved this algorithm byusing the simulated runoff data from hydrological modelThe time-series analysis showed that the ET estimation andWGHM simulation were in good consistency Howeveruncertainty of GRACE-based ET estimation increases for itsoverdependence on accuracy of hydrological model simu-lated variables such as runoff In addition Swenson andWahr[33] combined GRACE-based TWS changes together withthe measured runoff data to estimate the difference betweenprecipitation and evapotranspiration (119875 minus 119864) By comparingwith 119875 minus 119864 results of a land surface model (GLDAS-Noah)

4 Advances in Meteorology

they found that the errors of GLDAS-Noah estimation aremainly due to model force parameter of precipitation

33 Drought Analysis Based on time-series analysis ofGRACE-based TWS change with high temporal resolu-tion extreme hydrological disasters can be monitored andalarmed Droughts for regional and time-series water storagedeficit are the most serious natural hazards that can lead tocrop losses and economic havoc in many areas For droughtscan be regarded as terrestrial water storage (TWS) changesthat are related to integrated bulk variables analysis relyingupon subcomponents (eg precipitation) or proxies (egNDVI and CWSI) of TWS is insufficient Herewith anotherhydrological application of GRACE is severe droughts anal-ysis Combined with the measurements and hydrologicalmodel simulations Leblanc et al [34] used GRACE datato detect droughts in Southeastern Australia between 2001and 2008 Based on time-series analysis of TWS changes insummers from 2002 to 2007 2005 extreme drought eventin the Amazon river basin was detected [35] which wasregarded as the worst in over a century GRACE data is moresensitive to droughts than data-assimilating climate and landsurface models such as NECEP and GLDAS which demon-strated the unique potential of GRACE in monitoring large-scale severe drought events Validated by two independenthydrological estimates of GLDAS and ECMWF and directgravity observations from superconducting gravimeters the2003 excess terrestrial water storage depletion was observedfrom GRACE which can be related to the record-breakingheat wave that occurred in central Europe in 2003 [36]It indicated that GRACE data can be used in heat wavedisaster monitoring and evaluation whose essence is heatwave caused droughts analysis Combining with imageryremote sensing methods Frappart and Wilson et al appliedGRACE data to flood monitoring in several flood zones suchas the Mekong River Basin and the Amazon River Basin[37 38] However compared to droughts the water storagechanges based on GRACE data of extreme floods are lessresponsive which will bring more uncertainty in GRACE-based floods analysis [39]

34 Glacier Mass Balance Detection Driven by global changeand population pressure accelerating of glaciers meltingand sea level rise has been a serious global ecologicalproblem GRACE time-variable gravity field enabled directmeasurement of mass loss rates of both mountain glacierand polar glacier systems As noted by Wouters et al theGRACE solutions can be used to allow regional estimationof trends though assessing the mass loss to be dominated bysummer events rather than by a linear trend [40] GRACE-based glacier mass melting volume and rate estimation ofAntarctic and Greenland indicate that accelerating polarglacier melting contributes greatly to the current eustatic sealevel rise [41ndash43] Gardner et al have also found a rapidlyincreasing mass loss in the Canadian Arctic Archipelago(CAA) for the period 2004ndash2009 [44] Ice loss rate estimationon glaciers of Asia Alaska and other global mountains basedon GRACE data also agrees with the global tendency of

accelerating glacial loss Accelerated melting of mountainglaciers worldwide might be contributing to the global sealevel rise by 073 plusmn 010mmyr [45 46] Moreover GRACE-based TWS change can be used for researches of differentclimate variability impact [47 48] whereas for the postglacialrebound effects and unique set of gravity data GRACEmission provided ice sheet mass change estimation includeslarge uncertainties [49] Mass change rates estimated by dif-ferent GRACE solutions may vary by a factor of two or moreSo the glacier mass balance detection needs considerableprocessing to yield usable mass change data [49]

4 Discussion and Conclusions

Through ten years of development GRACE data has beenwidely applied in terrestrial hydrology monitoring Gravitysatellite provides newdata sets for hydrology researches basedon remote sensing technology Compared with other kindsof hydrological schemes GRACE can provide realistic spa-tiotemporal variations of vertically integrated measurementof water storage (groundwater soil moisture surface watersnow water vegetation water etc) at the precision of tens ofmm of equivalent water height at large scale However thehydrologicalmonitoring based onGRACEdata needs furtherresearch for example retrieval accuracy improvement morequantitative analyses rather than qualitative analyses and soforthThe focus of future development includes the followingaspects

(1) Improving the Accuracy of Gravity Satellite MeasurementsBecause of the limitations of GRACE satellite sensors inorbital altitude vertical gravity gradient measurements highfrequency signal aliasing and accuratemeasurement of time-varying gravity signals the accuracy and spatial resolutionof time-varying Earth gravity field signals at medium andlong wavelength of GRACE is low which reduced the TWSchange retrieval accuracy Therefore the development of keytechnology in gravity satellite sensors to improve accuracyand spatial resolution of satellite monitored gravity field isthe basis for a wider application in terrestrial hydrologymonitoring

(2) Water Storage Retrieval Models Research Recently theappropriate spatial resolution forGRACE-basedTWS changeis 400 km and the data accuracy is generally 15 cm Limitedby recent constraints of GRACE satellite improvement ofretrieval models is the only method for spatial resolutionand accuracy retrieval of TWS increases For example it isfeasible to improve TWS accuracy by the atmosphere andocean models improvement in data preprocessing reducingthe gravity field changes noises caused by factors unrelated toterrestrial water such as tides and circulation of atmosphereand ocean In addition by applying different filtering meth-ods such as anisotropicGaussian filtering and spherical radialbasis function filtering wavelet analysis in different researchareas can also improve the spatial resolution and accuracyof TWS retrieval Water storage retrieval techniques involvevarious aspects (eg GRACEdata preprocessing gravity fieldretrieval and TWS changes estimation) of the conversion

Advances in Meteorology 5

of GRACE gravity field data to TWS changes which are allimportant in TWS retrieval improvement

(3) Further Combination of GRACE Data with Associ-ated Hydrological Models For GRACE-based TWS changesretrieval does not involve the hydrological mechanisms it isnecessary to complement GRACE-based TWS by hydrologi-cal models for furthering its application in terrestrial hydrol-ogy monitoring Further combination of GRACE and hydro-logical models needs resolving their consistencies of spacetime and component Spatial consistency can be solvedby adjusting the calculation unit of hydrological models toreflect the spatial variability (such as distributed hydrologicalmodels) Temporal consistency requires analysis of upscalingGRACE data and downscaling hydrological models simula-tion Component consistency can be achieved by GRACE-based TWS signals subdivision or revising parameters ofhydrological models to TWS Through space time andcomponent consistency improvement the gravity field dataandmeasured data together can become basic dataset to forcehydrological models in the future

Appendices

A Water Storage Change Retrieval

Thechanges in terrestrial water storage result inmass redistri-bution in the Earthrsquos system thereby causing changes in thegravity field For a fixed continental region the changes inwater storage (including soil water and surface snow) comefrom rainfall evapotranspiration river transportation anddeep underground infiltration Except the rainfall which cancause increased water storage the remaining three processesall reduce it [10] Using the FG5 absolute gravimeter Zhanget al [50] measured the gravity change of nearly 10minus7msdotsminus2 attheWuhanUniversity site before and after a rainstorm whichclearly shows the influence of terrestrial water variation ongravity The Earthrsquos gravity field can be expressed as geoid

119873(120579 120582)

= 119886

infin

sum

119899=0

119899

sum

119898=0

[119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A1)

where 119899 and 119898 are harmonic degree and order of the gravityfield respectively 119886 is the Earthrsquos equatorial radius (about6371 km) 120579 and 120582 are colatitudes (the difference between90∘ and latitude) and longitude 119862

119899119898and 119878

119899119898are spherical

harmonic coefficients (dimensionless)119875119899119898

is the normalizedassociated Legendre functions The maximum value 119873 ofthe order 119899 of ideal gravity field should be infinite (119873 sim

infin) while the actual order of spherical harmonic coefficientsobtained by the gravity satellite has a finite value (119873 lt infin)and the spatial resolution of gravity field data is estimatedapproximately to be 120587119886119873 [51] Geoid height changes Δ119873

caused by the movement of substances on the Earthrsquos surfacecan be expressed as

Δ119873 (120579 120582)

= 119886

infin

sum

119899=0

119899

sum

119898=0

[Δ119862

119899119898cos (119898120582) + Δ119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A2)

where Δ119862119899119898

and Δ119878119899119898

are the changes of 119899-degree 119898-orderspherical harmonic coefficients of geoid and can be expressedas [5 52]

Δ119862

119899119898

Δ119878

119899119898

=

3

4120587119886120588

119886(2119899 + 1)

timesintΔ120588 (119903 120579 120582) 119875

119899119898(cos 120579)( 119903

119886

)

119899+2

cos (119898120582)sin (119898120582) sin 120579119889120579 119889120582 119889119903

(A3)

where 120588119886is the average density of the Earth (5517 kgm3)

and Δ120588(119903 120579 120582) is the change of bulk density at a particularlocation In gravity field inversion because the height changeof substances on the Earthrsquos surface 119867 is relatively smallcompared to the Earthrsquos average radius 119886 in gravity fieldretrieval ((119903119886) asymp 1) the changes of the gravity field directlycaused by the surface mass can be expressed as

Δ119862

119899119898

Δ119878

119899119898

surf

=

3

4120587119886120588

119886(2119899 + 1)

times intΔ120590 (120579 120582) 119875

119899119898(cos 120579) cos (119898120582)sin (119898120582) sin 120579119889120579 119889120582

(A4)

where Δ120590 is surface density change Δ120590 = intΔ120588(119903 120579 120582)119889119903Furthermore the surface mass variation in loads will causedeformation to the solid Earth which in turn can indirectlycause variations to the gravity field This can be expressed as[5 52]

Δ119862

119899119898

Δ119878

119899119898

soild

=

3119896

1015840

119899

4120587119886120588

119886(2119899 + 1)

times intΔ120590 (120579 120582) 119875

119899119898(cos 120579) cos (119898120582)sin (119898120582) sin 120579119889120579 119889120582

(A5)

where 119896

1015840

119899is load LOVE number of coefficients and the

specific value of 1198961015840119899can be found in relevant literature [11]

6 Advances in Meteorology

Thus the change of the Earthrsquos gravity field caused by massvariations on the Earthrsquos surface is given by

Δ119862

119899119898

Δ119878

119899119898

=

Δ119862

119899119898

Δ119878

119899119898

surf

+

Δ119862

119899119898

Δ119878

119899119898

soild

= (1 + 119896

1015840

119899)

Δ119862

119899119898

Δ119878

119899119898

surf

(A6)

If the spherical harmonic expansion is performed on thesurface density change Δ120590 then

Δ120590 (120579 120582)

= 119886120588

119908

infin

sum

119899=0

119899

sum

119898=0

[

119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A7)

where 120588119908is the density of water andΔ120590120588

119908can be considered

as mass variation on the Earthrsquos surface expressed in waterequivalent height Wahr et al [5] proposed that

Δ

119862

119899119898

Δ

119878

119899119898

=

120588

119886

3120588

119908

2119899 + 1

1 + 119896

1015840

119899

Δ119862

119899119898

Δ119878

119899119898

(A8)

The surface density changeΔ120590 can be calculated using thefollowing equation

Δ120590 (120579 120582)

=

119886120588

119886

3

infin

sum

119899=0

119899

sum

119898=0

2119899 + 1

1 + 119896

1015840

119899

[119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)]

times 119875

119899119898(cos 120579)

(A9)

For ocean and atmosphere mass variations are removedbased on Parallel Ocean Program (POP) model the aboveequation is the basic equation for the retrieval of surfacemassvariations based on spatiotemporal changes gravity fieldThe Earthrsquos surface density changes can be derived from thechanges of gravity field coefficients obtained from GRACEsatellites

B Evaluation Errors

Currently the latest available GRACE dataset product is theRL05 The accuracy of data provided by CSR and GFZ isbetter than that provided by JPL The evaluation errors ofGRACE are brought from satellite instrumentsmeasurementretrieval models and other factors as follows

(1) Gravity field data measured by GRACE satellite maybe contaminated by satellite measurement errors forthe influence of satellite orbit satellite K-band rang-ing and accelerometer measurement [20] The satel-lite measurement errors also include poor accuracyof C20 due to the insensitivity of track geometry to

the gravity fieldrsquos low degree gravitational variations[5 20] It is generally releasedwith removing variationof C20 [10] or replacing it by satellite laser ranging(SLR) substitution [20] In addition the missing offirst-degree spherical harmonic coefficients will alsobring error to GRACE It can commonly be resolvedby substituting value calculated from the term of theseasonal changes of the Earthrsquos mass center [53 54] orignoring its impact [55]

(2) In theory the retrieval of gravity field variation needsto use spherical harmonic coefficients of all degreesfrom 0 to infinity However gravity satellites can onlyprovide definite order data So the surface densitychange Δ120590 in retrieval models is treated by sphericalharmonic expansion to definite orders For the impactof high-order terms on the Earthrsquos surface densitychange Δ120590 cannot be ignored it results in truncationerrors in gravity field retrieval RL05 water storagedata is estimated by CSR using a retrieval modeltruncated to degree 60 [8] Zhu et al (2008) comparedthe global water storage retrieval results using modelstruncated to 15 degrees 20 degrees 35 degrees and60 degrees [56]They found that although some infor-mation of TWS change may be missing the retrievalresult of TWS change became more marked withlower truncation degree Generally the water storageretrieval truncated to order 60 is widely adopted [17]

(3) For terrestrial water monitoring focusing on themass changes of a particular area (eg river basin)it requires the integral process on density changeΔ120590 = ((intΔ120590(120579 120582)119906(120579 120582)119889Ω)Ω) The function ofregional characteristics 119906(120579 120582) is equal to 1 insidethe particular area and to zero outside The errorwill be brought for the discontinuity of 119906(120579 120582) in thedomain of integration In addition for the influenceof rapid increase of the errors of GRACE gravityfield model coefficients with increase of sphericalharmonic coefficients degree signal leakage errorsand the striping pollution [23] filtering methods areproposed to smooth GRACE data for noise reducingwhich will result in filtering errors of retrieval resultsProposed filtering methods include spatial averagingsymmetric Gaussian filtering optimized decorrela-tion filtering time-series method global hydrolog-ical model correction method kernel-independentcomponent analysis and optimal smoothing kernelmethod [53 57ndash62] Using filtering for the integraltreatment of surface density changes can effectivelyremove the striping to a certain extent Howeverthe obtained average surface density is critical for itreduces the useful energy of geophysical signals andresults in filtering errors In addition the existingfiltering methods require the support of a prioriknowledge (such as filtering radius and truncationdegree) Therefore in the actual retrieval process thefilter selection and parameter calibration require anunderstanding of the specific regional characteristics[60 63]

Advances in Meteorology 7

(4) TWS changes retrieval based on spatiotemporal vari-ations of gravity field remains considerable uncer-tainty which includes errors produced in the removalof tidal movement and the mass migration becauseof the atmosphere and ocean circulation [11] as wellas the errors in hydrological models used for theestimation of other terrestrial water parameters [6]

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project was supported by National Natural ScienceFoundation of China (Grant no 51309210) and the ChineseAcademy of Sciences (Grant no KZZD-EW-08)

References

[1] Y Huang D Jiang D Zhuang Y Zhu and J Fu ldquoAn improvedapproach for modeling spatial distribution of water use profitmdasha case study in Tuhai Majia Basin Chinardquo Ecological Indicatorsvol 36 pp 94ndash99 2014

[2] Y-H Huang D Jiang D-F Zhuang J-H Wang H-J Yangand H-Y Ren ldquoEvaluation of relative water use efficiency(RWUE) at a regional scale a case study of Tuhai-Majia BasinChinardquo Water Science and Technology vol 66 no 5 pp 927ndash933 2012

[3] J S Famiglietti ldquoRemote sensing of terrestrial water storagesoil moisture and surface watersrdquo in The State of the PlanetFrontiers and Challenges in Geophysics R S J Sparks and C JHawkesworth Eds pp 197ndash207 2004

[4] B D Tapley S Bettadpur M Watkins and C Reigber ldquoThegravity recovery and climate experiment mission overview andearly resultsrdquo Geophysical Research Letters vol 31 no 9 ArticleID L09607 2004

[5] J Wahr S Swenson V Zlotnicki and I Velicogna ldquoTime-variable gravity from GRACE first resultsrdquo GeophysicalResearch Letters vol 31 no 11 Article ID L11501 2004

[6] A Guntner ldquoImprovement of global hydrological models usingGRACE datardquo Surveys in Geophysics vol 29 no 4-5 pp 375ndash397 2008

[7] G Ramillien J S Famiglietti and J Wahr ldquoDetection ofcontinental hydrology and glaciology Signals from GRACE areviewrdquo Surveys inGeophysics vol 29 no 4-5 pp 361ndash374 2008

[8] D P Chambers ldquoConverting 11 Release-04 Gravity Coefficientsinto Maps of Equivalent Water Thicknessrdquo 2007 httpgrace-tellusjplnasagovfilesGRACE-dpc200711 RL04pdf

[9] M Becker W LLovel A Cazenave A Guntner and J-FCretaux ldquoRecent hydrological behavior of the East Africangreat lakes region inferred from GRACE satellite altimetry andrainfall observationsrdquo Comptes Rendus Geoscience vol 342 no3 pp 223ndash233 2010

[10] X Hu J Chen Y Zhou C Huang and X Liao ldquoSeasonal waterstorage change of the Yangtze River basin detected by GracerdquoScience in China D vol 49 no 5 pp 483ndash491 2006

[11] J Wahr M Molenaar and F Bryan ldquoTime variability ofthe Earths gravity field hydrological and oceanic effects and

their possible detection using GRACErdquo Journal of GeophysicalResearch B vol 103 no 12 pp 30205ndash30229 1998

[12] M Rodell and J S Famiglietti ldquoDetectability of variations incontinental water storage from satellite observations of the timedependent gravity fieldrdquo Water Resources Research vol 35 no9 pp 2705ndash2723 1999

[13] M Rodell and J S Famiglietti ldquoAn analysis of terrestrial waterstorage variations in Illinois with implications for the GravityRecovery and Climate Experiment (GRACE)rdquoWater ResourcesResearch vol 37 no 5 pp 1327ndash1339 2001

[14] M Zhong J Duan H Xu P Peng H Yan and Y ZhuldquoTrend of China land water storage redistribution at medi-and large-spatial scales in recent five years by satellite gravityobservationsrdquo Chinese Science Bulletin vol 54 no 5 pp 816ndash821 2009

[15] H Wang L Jia H Steffen et al ldquoIncreased water storage inNorth America and Scandinavia from GRACE gravity datardquoNature Geoscience vol 6 no 1 pp 38ndash42 2013

[16] S C Swenson and P C D Milly ldquoClimate model biases inseasonally of continental water storage revealed by satellitegravimetryrdquoWater Resources Research vol 42 no 3 Article IDW03201 2006

[17] T H Syed J S FamigliettiM Rodell J Chen andC RWilsonldquoAnalysis of terrestrial water storage changes from GRACE andGLDASrdquo Water Resources Research vol 44 no 2 Article IDW02433 2008

[18] G-Y Niu and Z-L Yang ldquoAssessing a land surface modelsimprovements with GRACE estimatesrdquo Geophysical ResearchLetters vol 33 no 7 Article ID L07401 2006

[19] T Ngo-Duc K Laval G Ramillien J Polcher and A CazenaveldquoValidation of the land water storage simulated by OrganisingCarbon and Hydrology in Dynamic Ecosystems (ORCHIDEE)with Gravity Recovery and Climate Experiment (GRACE)datardquo Water Resources Research vol 43 no 4 Article IDW04427 2007

[20] J L Chen C R Wilson B D Tapley and J C Ries ldquoLowdegree gravitational changes from GRACE validation andinterpretationrdquo Geophysical Research Letters vol 31 no 22Article ID L22607 pp 1ndash5 2004

[21] R Klees E A Revtova B C Gunter et al ldquoThe design of anoptimal filter for monthly GRACE gravity modelsrdquo GeophysicalJournal International vol 175 no 2 pp 417ndash432 2008

[22] K-W Seo C R Wilson J S Famiglietti J L Chen andM Rodell ldquoTerrestrial water mass load changes from GravityRecovery and Climate Experiment (GRACE)rdquoWater ResourcesResearch vol 42 no 5 Article ID W05417 2006

[23] B D Tapley S Bettadpur J C Ries P F Thompson and MM Watkins ldquoGRACE measurements of mass variability in theEarth systemrdquo Science vol 305 no 5683 pp 503ndash505 2004

[24] D P Lettenmaier and J S Famiglietti ldquoHydrology water fromon highrdquo Nature vol 444 no 7119 pp 562ndash563 2006

[25] S Swenson P J-F Yeh J Wahr and J Famiglietti ldquoA compari-son of terrestrial water storage variations from GRACE with insitu measurements from Illinoisrdquo Geophysical Research Lettersvol 33 no 16 Article ID L16401 2006

[26] L Xavier M Becker A Cazenave L Longuevergne W Lloveland O C R Filho ldquoInterannual variability in water storageover 2003ndash2008 in the Amazon Basin from GRACE spacegravimetry in situ river level and precipitation datardquo RemoteSensing of Environment vol 114 no 8 pp 1629ndash1637 2010

8 Advances in Meteorology

[27] M Rodell and J S Famiglietti ldquoThe potential for satellite-basedmonitoring of groundwater storage changes using GRACE theHigh Plains aquifer Central USrdquo Journal of Hydrology vol 263no 1ndash4 pp 245ndash256 2002

[28] G Strassberg B R Scanlon and M Rodell ldquoComparison ofseasonal terrestrial water storage variations from GRACE withgroundwater-level measurements from the High Plains Aquifer(USA)rdquo Geophysical Research Letters vol 34 no 14 Article IDL14402 2007

[29] M Rodell I Velicogna and J S Famiglietti ldquoSatellite-basedestimates of groundwater depletion in Indiardquo Nature vol 460no 7258 pp 999ndash1002 2009

[30] X Lu and Q Zhuang ldquoEvaluating evapotranspiration andwater-use efficiency of terrestrial ecosystems in the contermi-nous United States using MODIS and AmeriFlux datardquo RemoteSensing of Environment vol 114 no 9 pp 1924ndash1939 2010

[31] M Rodell J S Famiglietti J Chen et al ldquoBasin scale estimatesof evapotranspiration using GRACE and other observationsrdquoGeophysical Research Letters vol 31 no 20 Article ID L205042004

[32] G Ramillien F Frappart AGuntner TNgo-DucA Cazenaveand K Laval ldquoTime variations of the regional evapotranspi-ration rate from Gravity Recovery and Climate Experiment(GRACE) satellite gravimetryrdquo Water Resources Research vol42 no 10 Article ID W10403 2006

[33] S Swenson and J Wahr ldquoEstimating large-scale precipitationminus evapotranspiration from GRACE satellite gravity mea-surementsrdquo Journal of Hydrometeorology vol 7 no 2 pp 252ndash270 2006

[34] M Leblanc P Tregoning G Ramillien S O Tweed andA Fakes ldquoBasin-scale integrated observations of the early21st century multiyear drought in southeast Australiardquo WaterResources Research vol 45 no 4 Article IDW04408 2009

[35] J L Chen C R Wilson B D Tapley Z L Yang and GY Niu ldquo2005 drought event in the Amazon River basin asmeasured byGRACE and estimated by climatemodelsrdquo Journalof Geophysical Research B vol 114 no 5 Article ID B054042009

[36] O B Andersen S I Seneviratne J Hinderer and P ViterboldquoGRACE-derived terrestrial water storage depletion associatedwith the 2003 European heat waverdquo Geophysical ResearchLetters vol 32 no 18 Article ID L18405 pp 1ndash4 2005

[37] F Frappart K Do Minh J LHermitte et al ldquoWater volumechange in the lower Mekong from satellite altimetry andimagery datardquo Geophysical Journal International vol 167 no 2pp 570ndash584 2006

[38] M D Wilson P Bates D Alsdorf et al ldquoModeling large-scale inundation of Amazonian seasonally flooded wetlandsrdquoGeophysical Research Letters vol 34 no 15 Article ID L154042007

[39] S-C Han C K Shum C Jekeli and D Alsdorf ldquoImprovedestimation of terrestrial water storage changes from GRACErdquoGeophysical Research Letters vol 32 no 7 Article ID L07302pp 1ndash5 2005

[40] B Wouters D Chambers and E J O Schrama ldquoGRACEobserves small-scale mass loss in Greenlandrdquo GeophysicalResearch Letters vol 35 no 20 Article ID L20501 2008

[41] I Velicogna and J Wahr ldquoMeasurements of time-variablegravity showmass loss in Antarcticardquo Science vol 311 no 5768pp 1754ndash1756 2006

[42] D C Slobbe P Ditmar and R C Lindenbergh ldquoEstimatingthe rates of mass change ice volume change and snow volume

change in Greenland from ICESat and GRACE datardquo Geophys-ical Journal International vol 176 no 1 pp 95ndash106 2009

[43] P L Svendsen O B Andersen and A A Nielsen ldquoAccelerationof the Greenland ice sheet mass loss as observed by GRACEconfidence and sensitivityrdquo Earth and Planetary Science Lettersvol 364 pp 24ndash29 2013

[44] A S Gardner G Moholdt B Wouters et al ldquoSharply increasedmass loss from glaciers and ice caps in the Canadian ArcticArchipelagordquo Nature vol 473 no 7347 pp 357ndash360 2011

[45] J L Chen B D Tapley and C R Wilson ldquoAlaskan mountainglacial melting observed by satellite gravimetryrdquo Earth andPlanetary Science Letters vol 248 no 1-2 pp 353ndash363 2006

[46] K Matsuo and K Heki ldquoTime-variable ice loss in Asianhigh mountains from satellite gravimetryrdquo Earth and PlanetaryScience Letters vol 290 no 1-2 pp 30ndash36 2010

[47] D Garcıa-Garcıa C C Ummenhofer and V Zlotnicki ldquoAus-tralian water mass variations fromGRACE data linked to Indo-Pacific climate variabilityrdquo Remote Sensing of Environment vol115 no 9 pp 2175ndash2183 2011

[48] W W Immerzeel L P H van Beek and M F P BierkensldquoClimate change will affect the asian water towersrdquo Science vol328 no 5984 pp 1382ndash1385 2010

[49] L S Soslashrensen S B Simonsen K Nielsen et al ldquoMass balanceof the Greenland ice sheet (2003ndash2008) from ICESat datamdashtheimpact of interpolation sampling and firn densityrdquo Cryospherevol 5 no 1 pp 173ndash186 2011

[50] W Zhang Y Wang and C Zhang ldquoThe preliminary analysisof effects of the soil moisture on gravity observationsrdquo Carto-graphica Sinica vol 30 no 2 pp 108ndash111 2001

[51] G Ramillien J S Famiglietti and J Wahr ldquoDetection ofcontinental hydrology and glaciology signals from GRACE areviewrdquo Surveys inGeophysics vol 29 no 4-5 pp 361ndash374 2008

[52] J L Chen C R Wilson R J Eanes and B D TapleyldquoGeophysical contributions to satellite nodal residual variationrdquoJournal of Geophysical Research B vol 104 no 10 pp 23237ndash23244 1999

[53] J K Willis D P Chambers and R S Nerem ldquoAssessing theglobally averaged sea level budget on seasonal to interannualtimescalesrdquo Journal of Geophysical Research C vol 113 no 6Article ID C06015 2008

[54] E W Leuliette and L Miller ldquoClosing the sea level rise budgetwith altimetry Argo and Gracerdquo Geophysical Research Lettersvol 36 no 4 Article ID L04608 2009

[55] J L Chen C RWilson J S Famiglietti andMRodell ldquoAttenu-ation effect on seasonal basin-scale water storage changes fromGRACE time-variable gravityrdquo Journal of Geodesy vol 81 no 4pp 237ndash245 2007

[56] G Zhu J Li HWen and JWang ldquoStudy on variations of globalcontinental water storage with GRACE gravity field modelsrdquoJournal of Geodesy and Geodynamics vol 28 no 5 pp 39ndash442008

[57] S Swenson and J Wahr ldquoMethods for inferring regionalsurface-mass anomalies from Gravity Recovery and ClimateExperiment (GRACE) measurements of time-variable gravityrdquoJournal of Geophysical Research B vol 107 no 9 pp 3-1ndash3-132002

[58] S Swenson and J Wahr ldquoMonitoring changes in continentalwater storage with gracerdquo Space Science Reviews vol 108 no1-2 pp 345ndash354 2003

[59] K-W Seo and C RWilson ldquoSimulated estimation of hydrolog-ical loads fromGRACErdquo Journal of Geodesy vol 78 no 7-8 pp442ndash456 2005

Advances in Meteorology 9

[60] S Swenson and J Wahr ldquoPost-processing removal of correlatederrors in GRACE datardquoGeophysical Research Letters vol 33 no8 Article ID L08402 2006

[61] G Ramillien F Frappart A Cazenave and A Guntner ldquoTimevariations of land water storage from an inversion of 2 years ofGRACE geoidsrdquo Earth and Planetary Science Letters vol 235no 1-2 pp 283ndash301 2005

[62] F Frederic G Ramillien M Leblanc et al ldquoAn independentcomponent analysis filtering approach for estimating continen-tal hydrology in the GRACE gravity datardquo Remote Sensing ofEnvironment vol 115 no 1 pp 187ndash204 2011

[63] S Werth A Guntner R Schmidt and J Kusche ldquoEvaluation ofGRACE filter tools from a hydrological perspectiverdquo Geophysi-cal Journal International vol 179 no 3 pp 1499ndash1515 2009

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

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Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

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International Journal of

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OceanographyInternational Journal of

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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

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OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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MineralogyInternational Journal of

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Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Geological ResearchJournal of

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Geology Advances in

Advances in Meteorology 3

Yangtze River could reach a magnitude of 34 cm equivalentwater height with the maximum occurring in the springand early autumn Using 5-year GRACE-based TWS changedata in China Zhong et al [14] pointed out that the waterstorage in the north-central region of China diminished at anannual rate of 24 cm water equivalent height By combiningGRACE and GPS network observation data Wang et al [15]achieved precise retrieval of TWS change in Nordic regionand North America Their studies showed that over the pastdecade a sharp increase appeared in the water storage inNorthAmerica and Scandinavia and awater recovery processis underway

With further study GRACE data is now considered asan important parameter to assess and improve hydrologicalmodel simulation Swenson andMilly [16] and Syed et al [17]used GRACE data to verify and improve TWS simulation offive climate models and the Global Land Data AssimilationSystem (GLDAS) respectively Niu and Yang [18] and Ngo-Duc et al [19] used GRACE data for the result verifica-tion of common land surface model (CLM) of NCAR andORCHIDEE and corrected the CLM by applying GRACE-based TWS changes data

Various quantitative analyses between hydrological mod-els and GRACE-based TWS showed that the two simu-lation results of large areas are in good consistency ona seasonal or longer time scale [16 20 21] Time-seriesanalyses of South and North America Southeast Asia theGanges River Basin Africa Eurasia and other large-scaleregions all showed that GRACE-based TWS reflected asignificant seasonal variation However given the limitationsin the spatial resolution of GRACE data the consistencyof hydrological models and GRACE data in smaller areasis not satisfactory [22] Excluding the errors of GRACE-based TWS change retrieval the inconsistency is mainly dueto the simulation errors of various TWS components fromhydrological models For example the generalized deviationin estimating the important elements such as groundwatersurface water and soil water storage by using hydrologicalmodels resulted in smaller magnitudes in TWS changes Theerrors in the simulation of rainfall convergence and otherhydrological processes generated phase deviation in TWSchanges time series [17 23 24] In addition by combinationof the measured data of rainfall recharge soil water andgroundwater GRACE-based TWSwas used for water storagevariation of basin on interannual annual seasonal andmonthly time scales [25 26]

32 Hydrological Components Evaluation With the improve-ment of GRACE-based TWS change accuracy the GRACEdata is further used in hydrology and water resourcesresearch For specific areas TWS changes can be expressedas [10]

119889119882

119889119905

= 119875 minus 119864 minus 119877 (1)

where 119889119882119889119905 represents TWS changes and the correspond-ing equivalent water height can be obtained from GRACE119875 represents precipitation 119864 represents evapotranspiration

and119877 represents surface runoff By combiningGRACE-basedTWS changes hydrological models and the measured datathe water storage components including groundwater soilwater ET and 119875 minus 119864 can be estimated respectively

Groundwater estimation is difficult in remote sensingapplications in hydrology Optical remote sensing methodscan only combine measured data with spectral data toconstruct an empirical model for the estimation of ground-water changes whose groundwater retrieval accuracy is poorConsidering the contribution of groundwater changes toTWS variation groundwater remote sensing using GRACEwas feasible by combination with ancillary measurements ofsurface waters and soil moisture Rodell and Famiglietti [27]firstly used GRACE-based TWS change data soil water andother auxiliary data to analyze the possibility of monitoringgroundwater changes Swenson et al [25] studied the relationbetween measured value of groundwater plus soil water andGRACE-based TWS changes and presented the possibilityand sources of error in groundwater estimation based onGRACE data on multiple time scales Strassberg et al [28]compared the spatiotemporal correlation between GRACE-based TWS changes and hydrological model simulationsand field monitoring data and proposed the uncertainty ofGRACE-based groundwater retrieval The above studies sug-gest that for aquifers larger than 450000 km2 the accuracyof GRACE-based groundwater can reach 87mm Rodellet al applied GRACE data to the groundwater subsidencemonitoring in India and found that excessive irrigation andhuman activities caused the groundwater in the northwestprovinces of India to decline at an annual rate of 30 cmsim40 cm [29]

Evapotranspiration (ET) is an important process param-eter to studies of hydrology which is difficult to measure at aregional or continental scale Although ET can be indirectlyestimated using remote sensing data based on empiricalmod-els energy balancemodels or physicalmodels (eg Penman-Monteith equation) recent remote-sensed ET estimation isfar from satisfactory [30] For ET is a complex process thatrelated to many variables its estimation uncertainty basedon remote sensing data brings errors to ET retrieval resultsBased on terrestrial water balance at scale of river basinchanges of regional ET can be estimated by combining TWSchange from GRACE with observed precipitation (119875) andrunoff data (119877) Rodell et al [31] first used the measuredprecipitation and runoff data to verify the feasibility ofGRACE-based ET retrieval However the overdependenceon measured data restricts the applicability of this methodTherefore Ramillien et al [32] improved this algorithm byusing the simulated runoff data from hydrological modelThe time-series analysis showed that the ET estimation andWGHM simulation were in good consistency Howeveruncertainty of GRACE-based ET estimation increases for itsoverdependence on accuracy of hydrological model simu-lated variables such as runoff In addition Swenson andWahr[33] combined GRACE-based TWS changes together withthe measured runoff data to estimate the difference betweenprecipitation and evapotranspiration (119875 minus 119864) By comparingwith 119875 minus 119864 results of a land surface model (GLDAS-Noah)

4 Advances in Meteorology

they found that the errors of GLDAS-Noah estimation aremainly due to model force parameter of precipitation

33 Drought Analysis Based on time-series analysis ofGRACE-based TWS change with high temporal resolu-tion extreme hydrological disasters can be monitored andalarmed Droughts for regional and time-series water storagedeficit are the most serious natural hazards that can lead tocrop losses and economic havoc in many areas For droughtscan be regarded as terrestrial water storage (TWS) changesthat are related to integrated bulk variables analysis relyingupon subcomponents (eg precipitation) or proxies (egNDVI and CWSI) of TWS is insufficient Herewith anotherhydrological application of GRACE is severe droughts anal-ysis Combined with the measurements and hydrologicalmodel simulations Leblanc et al [34] used GRACE datato detect droughts in Southeastern Australia between 2001and 2008 Based on time-series analysis of TWS changes insummers from 2002 to 2007 2005 extreme drought eventin the Amazon river basin was detected [35] which wasregarded as the worst in over a century GRACE data is moresensitive to droughts than data-assimilating climate and landsurface models such as NECEP and GLDAS which demon-strated the unique potential of GRACE in monitoring large-scale severe drought events Validated by two independenthydrological estimates of GLDAS and ECMWF and directgravity observations from superconducting gravimeters the2003 excess terrestrial water storage depletion was observedfrom GRACE which can be related to the record-breakingheat wave that occurred in central Europe in 2003 [36]It indicated that GRACE data can be used in heat wavedisaster monitoring and evaluation whose essence is heatwave caused droughts analysis Combining with imageryremote sensing methods Frappart and Wilson et al appliedGRACE data to flood monitoring in several flood zones suchas the Mekong River Basin and the Amazon River Basin[37 38] However compared to droughts the water storagechanges based on GRACE data of extreme floods are lessresponsive which will bring more uncertainty in GRACE-based floods analysis [39]

34 Glacier Mass Balance Detection Driven by global changeand population pressure accelerating of glaciers meltingand sea level rise has been a serious global ecologicalproblem GRACE time-variable gravity field enabled directmeasurement of mass loss rates of both mountain glacierand polar glacier systems As noted by Wouters et al theGRACE solutions can be used to allow regional estimationof trends though assessing the mass loss to be dominated bysummer events rather than by a linear trend [40] GRACE-based glacier mass melting volume and rate estimation ofAntarctic and Greenland indicate that accelerating polarglacier melting contributes greatly to the current eustatic sealevel rise [41ndash43] Gardner et al have also found a rapidlyincreasing mass loss in the Canadian Arctic Archipelago(CAA) for the period 2004ndash2009 [44] Ice loss rate estimationon glaciers of Asia Alaska and other global mountains basedon GRACE data also agrees with the global tendency of

accelerating glacial loss Accelerated melting of mountainglaciers worldwide might be contributing to the global sealevel rise by 073 plusmn 010mmyr [45 46] Moreover GRACE-based TWS change can be used for researches of differentclimate variability impact [47 48] whereas for the postglacialrebound effects and unique set of gravity data GRACEmission provided ice sheet mass change estimation includeslarge uncertainties [49] Mass change rates estimated by dif-ferent GRACE solutions may vary by a factor of two or moreSo the glacier mass balance detection needs considerableprocessing to yield usable mass change data [49]

4 Discussion and Conclusions

Through ten years of development GRACE data has beenwidely applied in terrestrial hydrology monitoring Gravitysatellite provides newdata sets for hydrology researches basedon remote sensing technology Compared with other kindsof hydrological schemes GRACE can provide realistic spa-tiotemporal variations of vertically integrated measurementof water storage (groundwater soil moisture surface watersnow water vegetation water etc) at the precision of tens ofmm of equivalent water height at large scale However thehydrologicalmonitoring based onGRACEdata needs furtherresearch for example retrieval accuracy improvement morequantitative analyses rather than qualitative analyses and soforthThe focus of future development includes the followingaspects

(1) Improving the Accuracy of Gravity Satellite MeasurementsBecause of the limitations of GRACE satellite sensors inorbital altitude vertical gravity gradient measurements highfrequency signal aliasing and accuratemeasurement of time-varying gravity signals the accuracy and spatial resolutionof time-varying Earth gravity field signals at medium andlong wavelength of GRACE is low which reduced the TWSchange retrieval accuracy Therefore the development of keytechnology in gravity satellite sensors to improve accuracyand spatial resolution of satellite monitored gravity field isthe basis for a wider application in terrestrial hydrologymonitoring

(2) Water Storage Retrieval Models Research Recently theappropriate spatial resolution forGRACE-basedTWS changeis 400 km and the data accuracy is generally 15 cm Limitedby recent constraints of GRACE satellite improvement ofretrieval models is the only method for spatial resolutionand accuracy retrieval of TWS increases For example it isfeasible to improve TWS accuracy by the atmosphere andocean models improvement in data preprocessing reducingthe gravity field changes noises caused by factors unrelated toterrestrial water such as tides and circulation of atmosphereand ocean In addition by applying different filtering meth-ods such as anisotropicGaussian filtering and spherical radialbasis function filtering wavelet analysis in different researchareas can also improve the spatial resolution and accuracyof TWS retrieval Water storage retrieval techniques involvevarious aspects (eg GRACEdata preprocessing gravity fieldretrieval and TWS changes estimation) of the conversion

Advances in Meteorology 5

of GRACE gravity field data to TWS changes which are allimportant in TWS retrieval improvement

(3) Further Combination of GRACE Data with Associ-ated Hydrological Models For GRACE-based TWS changesretrieval does not involve the hydrological mechanisms it isnecessary to complement GRACE-based TWS by hydrologi-cal models for furthering its application in terrestrial hydrol-ogy monitoring Further combination of GRACE and hydro-logical models needs resolving their consistencies of spacetime and component Spatial consistency can be solvedby adjusting the calculation unit of hydrological models toreflect the spatial variability (such as distributed hydrologicalmodels) Temporal consistency requires analysis of upscalingGRACE data and downscaling hydrological models simula-tion Component consistency can be achieved by GRACE-based TWS signals subdivision or revising parameters ofhydrological models to TWS Through space time andcomponent consistency improvement the gravity field dataandmeasured data together can become basic dataset to forcehydrological models in the future

Appendices

A Water Storage Change Retrieval

Thechanges in terrestrial water storage result inmass redistri-bution in the Earthrsquos system thereby causing changes in thegravity field For a fixed continental region the changes inwater storage (including soil water and surface snow) comefrom rainfall evapotranspiration river transportation anddeep underground infiltration Except the rainfall which cancause increased water storage the remaining three processesall reduce it [10] Using the FG5 absolute gravimeter Zhanget al [50] measured the gravity change of nearly 10minus7msdotsminus2 attheWuhanUniversity site before and after a rainstorm whichclearly shows the influence of terrestrial water variation ongravity The Earthrsquos gravity field can be expressed as geoid

119873(120579 120582)

= 119886

infin

sum

119899=0

119899

sum

119898=0

[119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A1)

where 119899 and 119898 are harmonic degree and order of the gravityfield respectively 119886 is the Earthrsquos equatorial radius (about6371 km) 120579 and 120582 are colatitudes (the difference between90∘ and latitude) and longitude 119862

119899119898and 119878

119899119898are spherical

harmonic coefficients (dimensionless)119875119899119898

is the normalizedassociated Legendre functions The maximum value 119873 ofthe order 119899 of ideal gravity field should be infinite (119873 sim

infin) while the actual order of spherical harmonic coefficientsobtained by the gravity satellite has a finite value (119873 lt infin)and the spatial resolution of gravity field data is estimatedapproximately to be 120587119886119873 [51] Geoid height changes Δ119873

caused by the movement of substances on the Earthrsquos surfacecan be expressed as

Δ119873 (120579 120582)

= 119886

infin

sum

119899=0

119899

sum

119898=0

[Δ119862

119899119898cos (119898120582) + Δ119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A2)

where Δ119862119899119898

and Δ119878119899119898

are the changes of 119899-degree 119898-orderspherical harmonic coefficients of geoid and can be expressedas [5 52]

Δ119862

119899119898

Δ119878

119899119898

=

3

4120587119886120588

119886(2119899 + 1)

timesintΔ120588 (119903 120579 120582) 119875

119899119898(cos 120579)( 119903

119886

)

119899+2

cos (119898120582)sin (119898120582) sin 120579119889120579 119889120582 119889119903

(A3)

where 120588119886is the average density of the Earth (5517 kgm3)

and Δ120588(119903 120579 120582) is the change of bulk density at a particularlocation In gravity field inversion because the height changeof substances on the Earthrsquos surface 119867 is relatively smallcompared to the Earthrsquos average radius 119886 in gravity fieldretrieval ((119903119886) asymp 1) the changes of the gravity field directlycaused by the surface mass can be expressed as

Δ119862

119899119898

Δ119878

119899119898

surf

=

3

4120587119886120588

119886(2119899 + 1)

times intΔ120590 (120579 120582) 119875

119899119898(cos 120579) cos (119898120582)sin (119898120582) sin 120579119889120579 119889120582

(A4)

where Δ120590 is surface density change Δ120590 = intΔ120588(119903 120579 120582)119889119903Furthermore the surface mass variation in loads will causedeformation to the solid Earth which in turn can indirectlycause variations to the gravity field This can be expressed as[5 52]

Δ119862

119899119898

Δ119878

119899119898

soild

=

3119896

1015840

119899

4120587119886120588

119886(2119899 + 1)

times intΔ120590 (120579 120582) 119875

119899119898(cos 120579) cos (119898120582)sin (119898120582) sin 120579119889120579 119889120582

(A5)

where 119896

1015840

119899is load LOVE number of coefficients and the

specific value of 1198961015840119899can be found in relevant literature [11]

6 Advances in Meteorology

Thus the change of the Earthrsquos gravity field caused by massvariations on the Earthrsquos surface is given by

Δ119862

119899119898

Δ119878

119899119898

=

Δ119862

119899119898

Δ119878

119899119898

surf

+

Δ119862

119899119898

Δ119878

119899119898

soild

= (1 + 119896

1015840

119899)

Δ119862

119899119898

Δ119878

119899119898

surf

(A6)

If the spherical harmonic expansion is performed on thesurface density change Δ120590 then

Δ120590 (120579 120582)

= 119886120588

119908

infin

sum

119899=0

119899

sum

119898=0

[

119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A7)

where 120588119908is the density of water andΔ120590120588

119908can be considered

as mass variation on the Earthrsquos surface expressed in waterequivalent height Wahr et al [5] proposed that

Δ

119862

119899119898

Δ

119878

119899119898

=

120588

119886

3120588

119908

2119899 + 1

1 + 119896

1015840

119899

Δ119862

119899119898

Δ119878

119899119898

(A8)

The surface density changeΔ120590 can be calculated using thefollowing equation

Δ120590 (120579 120582)

=

119886120588

119886

3

infin

sum

119899=0

119899

sum

119898=0

2119899 + 1

1 + 119896

1015840

119899

[119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)]

times 119875

119899119898(cos 120579)

(A9)

For ocean and atmosphere mass variations are removedbased on Parallel Ocean Program (POP) model the aboveequation is the basic equation for the retrieval of surfacemassvariations based on spatiotemporal changes gravity fieldThe Earthrsquos surface density changes can be derived from thechanges of gravity field coefficients obtained from GRACEsatellites

B Evaluation Errors

Currently the latest available GRACE dataset product is theRL05 The accuracy of data provided by CSR and GFZ isbetter than that provided by JPL The evaluation errors ofGRACE are brought from satellite instrumentsmeasurementretrieval models and other factors as follows

(1) Gravity field data measured by GRACE satellite maybe contaminated by satellite measurement errors forthe influence of satellite orbit satellite K-band rang-ing and accelerometer measurement [20] The satel-lite measurement errors also include poor accuracyof C20 due to the insensitivity of track geometry to

the gravity fieldrsquos low degree gravitational variations[5 20] It is generally releasedwith removing variationof C20 [10] or replacing it by satellite laser ranging(SLR) substitution [20] In addition the missing offirst-degree spherical harmonic coefficients will alsobring error to GRACE It can commonly be resolvedby substituting value calculated from the term of theseasonal changes of the Earthrsquos mass center [53 54] orignoring its impact [55]

(2) In theory the retrieval of gravity field variation needsto use spherical harmonic coefficients of all degreesfrom 0 to infinity However gravity satellites can onlyprovide definite order data So the surface densitychange Δ120590 in retrieval models is treated by sphericalharmonic expansion to definite orders For the impactof high-order terms on the Earthrsquos surface densitychange Δ120590 cannot be ignored it results in truncationerrors in gravity field retrieval RL05 water storagedata is estimated by CSR using a retrieval modeltruncated to degree 60 [8] Zhu et al (2008) comparedthe global water storage retrieval results using modelstruncated to 15 degrees 20 degrees 35 degrees and60 degrees [56]They found that although some infor-mation of TWS change may be missing the retrievalresult of TWS change became more marked withlower truncation degree Generally the water storageretrieval truncated to order 60 is widely adopted [17]

(3) For terrestrial water monitoring focusing on themass changes of a particular area (eg river basin)it requires the integral process on density changeΔ120590 = ((intΔ120590(120579 120582)119906(120579 120582)119889Ω)Ω) The function ofregional characteristics 119906(120579 120582) is equal to 1 insidethe particular area and to zero outside The errorwill be brought for the discontinuity of 119906(120579 120582) in thedomain of integration In addition for the influenceof rapid increase of the errors of GRACE gravityfield model coefficients with increase of sphericalharmonic coefficients degree signal leakage errorsand the striping pollution [23] filtering methods areproposed to smooth GRACE data for noise reducingwhich will result in filtering errors of retrieval resultsProposed filtering methods include spatial averagingsymmetric Gaussian filtering optimized decorrela-tion filtering time-series method global hydrolog-ical model correction method kernel-independentcomponent analysis and optimal smoothing kernelmethod [53 57ndash62] Using filtering for the integraltreatment of surface density changes can effectivelyremove the striping to a certain extent Howeverthe obtained average surface density is critical for itreduces the useful energy of geophysical signals andresults in filtering errors In addition the existingfiltering methods require the support of a prioriknowledge (such as filtering radius and truncationdegree) Therefore in the actual retrieval process thefilter selection and parameter calibration require anunderstanding of the specific regional characteristics[60 63]

Advances in Meteorology 7

(4) TWS changes retrieval based on spatiotemporal vari-ations of gravity field remains considerable uncer-tainty which includes errors produced in the removalof tidal movement and the mass migration becauseof the atmosphere and ocean circulation [11] as wellas the errors in hydrological models used for theestimation of other terrestrial water parameters [6]

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project was supported by National Natural ScienceFoundation of China (Grant no 51309210) and the ChineseAcademy of Sciences (Grant no KZZD-EW-08)

References

[1] Y Huang D Jiang D Zhuang Y Zhu and J Fu ldquoAn improvedapproach for modeling spatial distribution of water use profitmdasha case study in Tuhai Majia Basin Chinardquo Ecological Indicatorsvol 36 pp 94ndash99 2014

[2] Y-H Huang D Jiang D-F Zhuang J-H Wang H-J Yangand H-Y Ren ldquoEvaluation of relative water use efficiency(RWUE) at a regional scale a case study of Tuhai-Majia BasinChinardquo Water Science and Technology vol 66 no 5 pp 927ndash933 2012

[3] J S Famiglietti ldquoRemote sensing of terrestrial water storagesoil moisture and surface watersrdquo in The State of the PlanetFrontiers and Challenges in Geophysics R S J Sparks and C JHawkesworth Eds pp 197ndash207 2004

[4] B D Tapley S Bettadpur M Watkins and C Reigber ldquoThegravity recovery and climate experiment mission overview andearly resultsrdquo Geophysical Research Letters vol 31 no 9 ArticleID L09607 2004

[5] J Wahr S Swenson V Zlotnicki and I Velicogna ldquoTime-variable gravity from GRACE first resultsrdquo GeophysicalResearch Letters vol 31 no 11 Article ID L11501 2004

[6] A Guntner ldquoImprovement of global hydrological models usingGRACE datardquo Surveys in Geophysics vol 29 no 4-5 pp 375ndash397 2008

[7] G Ramillien J S Famiglietti and J Wahr ldquoDetection ofcontinental hydrology and glaciology Signals from GRACE areviewrdquo Surveys inGeophysics vol 29 no 4-5 pp 361ndash374 2008

[8] D P Chambers ldquoConverting 11 Release-04 Gravity Coefficientsinto Maps of Equivalent Water Thicknessrdquo 2007 httpgrace-tellusjplnasagovfilesGRACE-dpc200711 RL04pdf

[9] M Becker W LLovel A Cazenave A Guntner and J-FCretaux ldquoRecent hydrological behavior of the East Africangreat lakes region inferred from GRACE satellite altimetry andrainfall observationsrdquo Comptes Rendus Geoscience vol 342 no3 pp 223ndash233 2010

[10] X Hu J Chen Y Zhou C Huang and X Liao ldquoSeasonal waterstorage change of the Yangtze River basin detected by GracerdquoScience in China D vol 49 no 5 pp 483ndash491 2006

[11] J Wahr M Molenaar and F Bryan ldquoTime variability ofthe Earths gravity field hydrological and oceanic effects and

their possible detection using GRACErdquo Journal of GeophysicalResearch B vol 103 no 12 pp 30205ndash30229 1998

[12] M Rodell and J S Famiglietti ldquoDetectability of variations incontinental water storage from satellite observations of the timedependent gravity fieldrdquo Water Resources Research vol 35 no9 pp 2705ndash2723 1999

[13] M Rodell and J S Famiglietti ldquoAn analysis of terrestrial waterstorage variations in Illinois with implications for the GravityRecovery and Climate Experiment (GRACE)rdquoWater ResourcesResearch vol 37 no 5 pp 1327ndash1339 2001

[14] M Zhong J Duan H Xu P Peng H Yan and Y ZhuldquoTrend of China land water storage redistribution at medi-and large-spatial scales in recent five years by satellite gravityobservationsrdquo Chinese Science Bulletin vol 54 no 5 pp 816ndash821 2009

[15] H Wang L Jia H Steffen et al ldquoIncreased water storage inNorth America and Scandinavia from GRACE gravity datardquoNature Geoscience vol 6 no 1 pp 38ndash42 2013

[16] S C Swenson and P C D Milly ldquoClimate model biases inseasonally of continental water storage revealed by satellitegravimetryrdquoWater Resources Research vol 42 no 3 Article IDW03201 2006

[17] T H Syed J S FamigliettiM Rodell J Chen andC RWilsonldquoAnalysis of terrestrial water storage changes from GRACE andGLDASrdquo Water Resources Research vol 44 no 2 Article IDW02433 2008

[18] G-Y Niu and Z-L Yang ldquoAssessing a land surface modelsimprovements with GRACE estimatesrdquo Geophysical ResearchLetters vol 33 no 7 Article ID L07401 2006

[19] T Ngo-Duc K Laval G Ramillien J Polcher and A CazenaveldquoValidation of the land water storage simulated by OrganisingCarbon and Hydrology in Dynamic Ecosystems (ORCHIDEE)with Gravity Recovery and Climate Experiment (GRACE)datardquo Water Resources Research vol 43 no 4 Article IDW04427 2007

[20] J L Chen C R Wilson B D Tapley and J C Ries ldquoLowdegree gravitational changes from GRACE validation andinterpretationrdquo Geophysical Research Letters vol 31 no 22Article ID L22607 pp 1ndash5 2004

[21] R Klees E A Revtova B C Gunter et al ldquoThe design of anoptimal filter for monthly GRACE gravity modelsrdquo GeophysicalJournal International vol 175 no 2 pp 417ndash432 2008

[22] K-W Seo C R Wilson J S Famiglietti J L Chen andM Rodell ldquoTerrestrial water mass load changes from GravityRecovery and Climate Experiment (GRACE)rdquoWater ResourcesResearch vol 42 no 5 Article ID W05417 2006

[23] B D Tapley S Bettadpur J C Ries P F Thompson and MM Watkins ldquoGRACE measurements of mass variability in theEarth systemrdquo Science vol 305 no 5683 pp 503ndash505 2004

[24] D P Lettenmaier and J S Famiglietti ldquoHydrology water fromon highrdquo Nature vol 444 no 7119 pp 562ndash563 2006

[25] S Swenson P J-F Yeh J Wahr and J Famiglietti ldquoA compari-son of terrestrial water storage variations from GRACE with insitu measurements from Illinoisrdquo Geophysical Research Lettersvol 33 no 16 Article ID L16401 2006

[26] L Xavier M Becker A Cazenave L Longuevergne W Lloveland O C R Filho ldquoInterannual variability in water storageover 2003ndash2008 in the Amazon Basin from GRACE spacegravimetry in situ river level and precipitation datardquo RemoteSensing of Environment vol 114 no 8 pp 1629ndash1637 2010

8 Advances in Meteorology

[27] M Rodell and J S Famiglietti ldquoThe potential for satellite-basedmonitoring of groundwater storage changes using GRACE theHigh Plains aquifer Central USrdquo Journal of Hydrology vol 263no 1ndash4 pp 245ndash256 2002

[28] G Strassberg B R Scanlon and M Rodell ldquoComparison ofseasonal terrestrial water storage variations from GRACE withgroundwater-level measurements from the High Plains Aquifer(USA)rdquo Geophysical Research Letters vol 34 no 14 Article IDL14402 2007

[29] M Rodell I Velicogna and J S Famiglietti ldquoSatellite-basedestimates of groundwater depletion in Indiardquo Nature vol 460no 7258 pp 999ndash1002 2009

[30] X Lu and Q Zhuang ldquoEvaluating evapotranspiration andwater-use efficiency of terrestrial ecosystems in the contermi-nous United States using MODIS and AmeriFlux datardquo RemoteSensing of Environment vol 114 no 9 pp 1924ndash1939 2010

[31] M Rodell J S Famiglietti J Chen et al ldquoBasin scale estimatesof evapotranspiration using GRACE and other observationsrdquoGeophysical Research Letters vol 31 no 20 Article ID L205042004

[32] G Ramillien F Frappart AGuntner TNgo-DucA Cazenaveand K Laval ldquoTime variations of the regional evapotranspi-ration rate from Gravity Recovery and Climate Experiment(GRACE) satellite gravimetryrdquo Water Resources Research vol42 no 10 Article ID W10403 2006

[33] S Swenson and J Wahr ldquoEstimating large-scale precipitationminus evapotranspiration from GRACE satellite gravity mea-surementsrdquo Journal of Hydrometeorology vol 7 no 2 pp 252ndash270 2006

[34] M Leblanc P Tregoning G Ramillien S O Tweed andA Fakes ldquoBasin-scale integrated observations of the early21st century multiyear drought in southeast Australiardquo WaterResources Research vol 45 no 4 Article IDW04408 2009

[35] J L Chen C R Wilson B D Tapley Z L Yang and GY Niu ldquo2005 drought event in the Amazon River basin asmeasured byGRACE and estimated by climatemodelsrdquo Journalof Geophysical Research B vol 114 no 5 Article ID B054042009

[36] O B Andersen S I Seneviratne J Hinderer and P ViterboldquoGRACE-derived terrestrial water storage depletion associatedwith the 2003 European heat waverdquo Geophysical ResearchLetters vol 32 no 18 Article ID L18405 pp 1ndash4 2005

[37] F Frappart K Do Minh J LHermitte et al ldquoWater volumechange in the lower Mekong from satellite altimetry andimagery datardquo Geophysical Journal International vol 167 no 2pp 570ndash584 2006

[38] M D Wilson P Bates D Alsdorf et al ldquoModeling large-scale inundation of Amazonian seasonally flooded wetlandsrdquoGeophysical Research Letters vol 34 no 15 Article ID L154042007

[39] S-C Han C K Shum C Jekeli and D Alsdorf ldquoImprovedestimation of terrestrial water storage changes from GRACErdquoGeophysical Research Letters vol 32 no 7 Article ID L07302pp 1ndash5 2005

[40] B Wouters D Chambers and E J O Schrama ldquoGRACEobserves small-scale mass loss in Greenlandrdquo GeophysicalResearch Letters vol 35 no 20 Article ID L20501 2008

[41] I Velicogna and J Wahr ldquoMeasurements of time-variablegravity showmass loss in Antarcticardquo Science vol 311 no 5768pp 1754ndash1756 2006

[42] D C Slobbe P Ditmar and R C Lindenbergh ldquoEstimatingthe rates of mass change ice volume change and snow volume

change in Greenland from ICESat and GRACE datardquo Geophys-ical Journal International vol 176 no 1 pp 95ndash106 2009

[43] P L Svendsen O B Andersen and A A Nielsen ldquoAccelerationof the Greenland ice sheet mass loss as observed by GRACEconfidence and sensitivityrdquo Earth and Planetary Science Lettersvol 364 pp 24ndash29 2013

[44] A S Gardner G Moholdt B Wouters et al ldquoSharply increasedmass loss from glaciers and ice caps in the Canadian ArcticArchipelagordquo Nature vol 473 no 7347 pp 357ndash360 2011

[45] J L Chen B D Tapley and C R Wilson ldquoAlaskan mountainglacial melting observed by satellite gravimetryrdquo Earth andPlanetary Science Letters vol 248 no 1-2 pp 353ndash363 2006

[46] K Matsuo and K Heki ldquoTime-variable ice loss in Asianhigh mountains from satellite gravimetryrdquo Earth and PlanetaryScience Letters vol 290 no 1-2 pp 30ndash36 2010

[47] D Garcıa-Garcıa C C Ummenhofer and V Zlotnicki ldquoAus-tralian water mass variations fromGRACE data linked to Indo-Pacific climate variabilityrdquo Remote Sensing of Environment vol115 no 9 pp 2175ndash2183 2011

[48] W W Immerzeel L P H van Beek and M F P BierkensldquoClimate change will affect the asian water towersrdquo Science vol328 no 5984 pp 1382ndash1385 2010

[49] L S Soslashrensen S B Simonsen K Nielsen et al ldquoMass balanceof the Greenland ice sheet (2003ndash2008) from ICESat datamdashtheimpact of interpolation sampling and firn densityrdquo Cryospherevol 5 no 1 pp 173ndash186 2011

[50] W Zhang Y Wang and C Zhang ldquoThe preliminary analysisof effects of the soil moisture on gravity observationsrdquo Carto-graphica Sinica vol 30 no 2 pp 108ndash111 2001

[51] G Ramillien J S Famiglietti and J Wahr ldquoDetection ofcontinental hydrology and glaciology signals from GRACE areviewrdquo Surveys inGeophysics vol 29 no 4-5 pp 361ndash374 2008

[52] J L Chen C R Wilson R J Eanes and B D TapleyldquoGeophysical contributions to satellite nodal residual variationrdquoJournal of Geophysical Research B vol 104 no 10 pp 23237ndash23244 1999

[53] J K Willis D P Chambers and R S Nerem ldquoAssessing theglobally averaged sea level budget on seasonal to interannualtimescalesrdquo Journal of Geophysical Research C vol 113 no 6Article ID C06015 2008

[54] E W Leuliette and L Miller ldquoClosing the sea level rise budgetwith altimetry Argo and Gracerdquo Geophysical Research Lettersvol 36 no 4 Article ID L04608 2009

[55] J L Chen C RWilson J S Famiglietti andMRodell ldquoAttenu-ation effect on seasonal basin-scale water storage changes fromGRACE time-variable gravityrdquo Journal of Geodesy vol 81 no 4pp 237ndash245 2007

[56] G Zhu J Li HWen and JWang ldquoStudy on variations of globalcontinental water storage with GRACE gravity field modelsrdquoJournal of Geodesy and Geodynamics vol 28 no 5 pp 39ndash442008

[57] S Swenson and J Wahr ldquoMethods for inferring regionalsurface-mass anomalies from Gravity Recovery and ClimateExperiment (GRACE) measurements of time-variable gravityrdquoJournal of Geophysical Research B vol 107 no 9 pp 3-1ndash3-132002

[58] S Swenson and J Wahr ldquoMonitoring changes in continentalwater storage with gracerdquo Space Science Reviews vol 108 no1-2 pp 345ndash354 2003

[59] K-W Seo and C RWilson ldquoSimulated estimation of hydrolog-ical loads fromGRACErdquo Journal of Geodesy vol 78 no 7-8 pp442ndash456 2005

Advances in Meteorology 9

[60] S Swenson and J Wahr ldquoPost-processing removal of correlatederrors in GRACE datardquoGeophysical Research Letters vol 33 no8 Article ID L08402 2006

[61] G Ramillien F Frappart A Cazenave and A Guntner ldquoTimevariations of land water storage from an inversion of 2 years ofGRACE geoidsrdquo Earth and Planetary Science Letters vol 235no 1-2 pp 283ndash301 2005

[62] F Frederic G Ramillien M Leblanc et al ldquoAn independentcomponent analysis filtering approach for estimating continen-tal hydrology in the GRACE gravity datardquo Remote Sensing ofEnvironment vol 115 no 1 pp 187ndash204 2011

[63] S Werth A Guntner R Schmidt and J Kusche ldquoEvaluation ofGRACE filter tools from a hydrological perspectiverdquo Geophysi-cal Journal International vol 179 no 3 pp 1499ndash1515 2009

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Applied ampEnvironmentalSoil Science

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MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

4 Advances in Meteorology

they found that the errors of GLDAS-Noah estimation aremainly due to model force parameter of precipitation

33 Drought Analysis Based on time-series analysis ofGRACE-based TWS change with high temporal resolu-tion extreme hydrological disasters can be monitored andalarmed Droughts for regional and time-series water storagedeficit are the most serious natural hazards that can lead tocrop losses and economic havoc in many areas For droughtscan be regarded as terrestrial water storage (TWS) changesthat are related to integrated bulk variables analysis relyingupon subcomponents (eg precipitation) or proxies (egNDVI and CWSI) of TWS is insufficient Herewith anotherhydrological application of GRACE is severe droughts anal-ysis Combined with the measurements and hydrologicalmodel simulations Leblanc et al [34] used GRACE datato detect droughts in Southeastern Australia between 2001and 2008 Based on time-series analysis of TWS changes insummers from 2002 to 2007 2005 extreme drought eventin the Amazon river basin was detected [35] which wasregarded as the worst in over a century GRACE data is moresensitive to droughts than data-assimilating climate and landsurface models such as NECEP and GLDAS which demon-strated the unique potential of GRACE in monitoring large-scale severe drought events Validated by two independenthydrological estimates of GLDAS and ECMWF and directgravity observations from superconducting gravimeters the2003 excess terrestrial water storage depletion was observedfrom GRACE which can be related to the record-breakingheat wave that occurred in central Europe in 2003 [36]It indicated that GRACE data can be used in heat wavedisaster monitoring and evaluation whose essence is heatwave caused droughts analysis Combining with imageryremote sensing methods Frappart and Wilson et al appliedGRACE data to flood monitoring in several flood zones suchas the Mekong River Basin and the Amazon River Basin[37 38] However compared to droughts the water storagechanges based on GRACE data of extreme floods are lessresponsive which will bring more uncertainty in GRACE-based floods analysis [39]

34 Glacier Mass Balance Detection Driven by global changeand population pressure accelerating of glaciers meltingand sea level rise has been a serious global ecologicalproblem GRACE time-variable gravity field enabled directmeasurement of mass loss rates of both mountain glacierand polar glacier systems As noted by Wouters et al theGRACE solutions can be used to allow regional estimationof trends though assessing the mass loss to be dominated bysummer events rather than by a linear trend [40] GRACE-based glacier mass melting volume and rate estimation ofAntarctic and Greenland indicate that accelerating polarglacier melting contributes greatly to the current eustatic sealevel rise [41ndash43] Gardner et al have also found a rapidlyincreasing mass loss in the Canadian Arctic Archipelago(CAA) for the period 2004ndash2009 [44] Ice loss rate estimationon glaciers of Asia Alaska and other global mountains basedon GRACE data also agrees with the global tendency of

accelerating glacial loss Accelerated melting of mountainglaciers worldwide might be contributing to the global sealevel rise by 073 plusmn 010mmyr [45 46] Moreover GRACE-based TWS change can be used for researches of differentclimate variability impact [47 48] whereas for the postglacialrebound effects and unique set of gravity data GRACEmission provided ice sheet mass change estimation includeslarge uncertainties [49] Mass change rates estimated by dif-ferent GRACE solutions may vary by a factor of two or moreSo the glacier mass balance detection needs considerableprocessing to yield usable mass change data [49]

4 Discussion and Conclusions

Through ten years of development GRACE data has beenwidely applied in terrestrial hydrology monitoring Gravitysatellite provides newdata sets for hydrology researches basedon remote sensing technology Compared with other kindsof hydrological schemes GRACE can provide realistic spa-tiotemporal variations of vertically integrated measurementof water storage (groundwater soil moisture surface watersnow water vegetation water etc) at the precision of tens ofmm of equivalent water height at large scale However thehydrologicalmonitoring based onGRACEdata needs furtherresearch for example retrieval accuracy improvement morequantitative analyses rather than qualitative analyses and soforthThe focus of future development includes the followingaspects

(1) Improving the Accuracy of Gravity Satellite MeasurementsBecause of the limitations of GRACE satellite sensors inorbital altitude vertical gravity gradient measurements highfrequency signal aliasing and accuratemeasurement of time-varying gravity signals the accuracy and spatial resolutionof time-varying Earth gravity field signals at medium andlong wavelength of GRACE is low which reduced the TWSchange retrieval accuracy Therefore the development of keytechnology in gravity satellite sensors to improve accuracyand spatial resolution of satellite monitored gravity field isthe basis for a wider application in terrestrial hydrologymonitoring

(2) Water Storage Retrieval Models Research Recently theappropriate spatial resolution forGRACE-basedTWS changeis 400 km and the data accuracy is generally 15 cm Limitedby recent constraints of GRACE satellite improvement ofretrieval models is the only method for spatial resolutionand accuracy retrieval of TWS increases For example it isfeasible to improve TWS accuracy by the atmosphere andocean models improvement in data preprocessing reducingthe gravity field changes noises caused by factors unrelated toterrestrial water such as tides and circulation of atmosphereand ocean In addition by applying different filtering meth-ods such as anisotropicGaussian filtering and spherical radialbasis function filtering wavelet analysis in different researchareas can also improve the spatial resolution and accuracyof TWS retrieval Water storage retrieval techniques involvevarious aspects (eg GRACEdata preprocessing gravity fieldretrieval and TWS changes estimation) of the conversion

Advances in Meteorology 5

of GRACE gravity field data to TWS changes which are allimportant in TWS retrieval improvement

(3) Further Combination of GRACE Data with Associ-ated Hydrological Models For GRACE-based TWS changesretrieval does not involve the hydrological mechanisms it isnecessary to complement GRACE-based TWS by hydrologi-cal models for furthering its application in terrestrial hydrol-ogy monitoring Further combination of GRACE and hydro-logical models needs resolving their consistencies of spacetime and component Spatial consistency can be solvedby adjusting the calculation unit of hydrological models toreflect the spatial variability (such as distributed hydrologicalmodels) Temporal consistency requires analysis of upscalingGRACE data and downscaling hydrological models simula-tion Component consistency can be achieved by GRACE-based TWS signals subdivision or revising parameters ofhydrological models to TWS Through space time andcomponent consistency improvement the gravity field dataandmeasured data together can become basic dataset to forcehydrological models in the future

Appendices

A Water Storage Change Retrieval

Thechanges in terrestrial water storage result inmass redistri-bution in the Earthrsquos system thereby causing changes in thegravity field For a fixed continental region the changes inwater storage (including soil water and surface snow) comefrom rainfall evapotranspiration river transportation anddeep underground infiltration Except the rainfall which cancause increased water storage the remaining three processesall reduce it [10] Using the FG5 absolute gravimeter Zhanget al [50] measured the gravity change of nearly 10minus7msdotsminus2 attheWuhanUniversity site before and after a rainstorm whichclearly shows the influence of terrestrial water variation ongravity The Earthrsquos gravity field can be expressed as geoid

119873(120579 120582)

= 119886

infin

sum

119899=0

119899

sum

119898=0

[119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A1)

where 119899 and 119898 are harmonic degree and order of the gravityfield respectively 119886 is the Earthrsquos equatorial radius (about6371 km) 120579 and 120582 are colatitudes (the difference between90∘ and latitude) and longitude 119862

119899119898and 119878

119899119898are spherical

harmonic coefficients (dimensionless)119875119899119898

is the normalizedassociated Legendre functions The maximum value 119873 ofthe order 119899 of ideal gravity field should be infinite (119873 sim

infin) while the actual order of spherical harmonic coefficientsobtained by the gravity satellite has a finite value (119873 lt infin)and the spatial resolution of gravity field data is estimatedapproximately to be 120587119886119873 [51] Geoid height changes Δ119873

caused by the movement of substances on the Earthrsquos surfacecan be expressed as

Δ119873 (120579 120582)

= 119886

infin

sum

119899=0

119899

sum

119898=0

[Δ119862

119899119898cos (119898120582) + Δ119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A2)

where Δ119862119899119898

and Δ119878119899119898

are the changes of 119899-degree 119898-orderspherical harmonic coefficients of geoid and can be expressedas [5 52]

Δ119862

119899119898

Δ119878

119899119898

=

3

4120587119886120588

119886(2119899 + 1)

timesintΔ120588 (119903 120579 120582) 119875

119899119898(cos 120579)( 119903

119886

)

119899+2

cos (119898120582)sin (119898120582) sin 120579119889120579 119889120582 119889119903

(A3)

where 120588119886is the average density of the Earth (5517 kgm3)

and Δ120588(119903 120579 120582) is the change of bulk density at a particularlocation In gravity field inversion because the height changeof substances on the Earthrsquos surface 119867 is relatively smallcompared to the Earthrsquos average radius 119886 in gravity fieldretrieval ((119903119886) asymp 1) the changes of the gravity field directlycaused by the surface mass can be expressed as

Δ119862

119899119898

Δ119878

119899119898

surf

=

3

4120587119886120588

119886(2119899 + 1)

times intΔ120590 (120579 120582) 119875

119899119898(cos 120579) cos (119898120582)sin (119898120582) sin 120579119889120579 119889120582

(A4)

where Δ120590 is surface density change Δ120590 = intΔ120588(119903 120579 120582)119889119903Furthermore the surface mass variation in loads will causedeformation to the solid Earth which in turn can indirectlycause variations to the gravity field This can be expressed as[5 52]

Δ119862

119899119898

Δ119878

119899119898

soild

=

3119896

1015840

119899

4120587119886120588

119886(2119899 + 1)

times intΔ120590 (120579 120582) 119875

119899119898(cos 120579) cos (119898120582)sin (119898120582) sin 120579119889120579 119889120582

(A5)

where 119896

1015840

119899is load LOVE number of coefficients and the

specific value of 1198961015840119899can be found in relevant literature [11]

6 Advances in Meteorology

Thus the change of the Earthrsquos gravity field caused by massvariations on the Earthrsquos surface is given by

Δ119862

119899119898

Δ119878

119899119898

=

Δ119862

119899119898

Δ119878

119899119898

surf

+

Δ119862

119899119898

Δ119878

119899119898

soild

= (1 + 119896

1015840

119899)

Δ119862

119899119898

Δ119878

119899119898

surf

(A6)

If the spherical harmonic expansion is performed on thesurface density change Δ120590 then

Δ120590 (120579 120582)

= 119886120588

119908

infin

sum

119899=0

119899

sum

119898=0

[

119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A7)

where 120588119908is the density of water andΔ120590120588

119908can be considered

as mass variation on the Earthrsquos surface expressed in waterequivalent height Wahr et al [5] proposed that

Δ

119862

119899119898

Δ

119878

119899119898

=

120588

119886

3120588

119908

2119899 + 1

1 + 119896

1015840

119899

Δ119862

119899119898

Δ119878

119899119898

(A8)

The surface density changeΔ120590 can be calculated using thefollowing equation

Δ120590 (120579 120582)

=

119886120588

119886

3

infin

sum

119899=0

119899

sum

119898=0

2119899 + 1

1 + 119896

1015840

119899

[119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)]

times 119875

119899119898(cos 120579)

(A9)

For ocean and atmosphere mass variations are removedbased on Parallel Ocean Program (POP) model the aboveequation is the basic equation for the retrieval of surfacemassvariations based on spatiotemporal changes gravity fieldThe Earthrsquos surface density changes can be derived from thechanges of gravity field coefficients obtained from GRACEsatellites

B Evaluation Errors

Currently the latest available GRACE dataset product is theRL05 The accuracy of data provided by CSR and GFZ isbetter than that provided by JPL The evaluation errors ofGRACE are brought from satellite instrumentsmeasurementretrieval models and other factors as follows

(1) Gravity field data measured by GRACE satellite maybe contaminated by satellite measurement errors forthe influence of satellite orbit satellite K-band rang-ing and accelerometer measurement [20] The satel-lite measurement errors also include poor accuracyof C20 due to the insensitivity of track geometry to

the gravity fieldrsquos low degree gravitational variations[5 20] It is generally releasedwith removing variationof C20 [10] or replacing it by satellite laser ranging(SLR) substitution [20] In addition the missing offirst-degree spherical harmonic coefficients will alsobring error to GRACE It can commonly be resolvedby substituting value calculated from the term of theseasonal changes of the Earthrsquos mass center [53 54] orignoring its impact [55]

(2) In theory the retrieval of gravity field variation needsto use spherical harmonic coefficients of all degreesfrom 0 to infinity However gravity satellites can onlyprovide definite order data So the surface densitychange Δ120590 in retrieval models is treated by sphericalharmonic expansion to definite orders For the impactof high-order terms on the Earthrsquos surface densitychange Δ120590 cannot be ignored it results in truncationerrors in gravity field retrieval RL05 water storagedata is estimated by CSR using a retrieval modeltruncated to degree 60 [8] Zhu et al (2008) comparedthe global water storage retrieval results using modelstruncated to 15 degrees 20 degrees 35 degrees and60 degrees [56]They found that although some infor-mation of TWS change may be missing the retrievalresult of TWS change became more marked withlower truncation degree Generally the water storageretrieval truncated to order 60 is widely adopted [17]

(3) For terrestrial water monitoring focusing on themass changes of a particular area (eg river basin)it requires the integral process on density changeΔ120590 = ((intΔ120590(120579 120582)119906(120579 120582)119889Ω)Ω) The function ofregional characteristics 119906(120579 120582) is equal to 1 insidethe particular area and to zero outside The errorwill be brought for the discontinuity of 119906(120579 120582) in thedomain of integration In addition for the influenceof rapid increase of the errors of GRACE gravityfield model coefficients with increase of sphericalharmonic coefficients degree signal leakage errorsand the striping pollution [23] filtering methods areproposed to smooth GRACE data for noise reducingwhich will result in filtering errors of retrieval resultsProposed filtering methods include spatial averagingsymmetric Gaussian filtering optimized decorrela-tion filtering time-series method global hydrolog-ical model correction method kernel-independentcomponent analysis and optimal smoothing kernelmethod [53 57ndash62] Using filtering for the integraltreatment of surface density changes can effectivelyremove the striping to a certain extent Howeverthe obtained average surface density is critical for itreduces the useful energy of geophysical signals andresults in filtering errors In addition the existingfiltering methods require the support of a prioriknowledge (such as filtering radius and truncationdegree) Therefore in the actual retrieval process thefilter selection and parameter calibration require anunderstanding of the specific regional characteristics[60 63]

Advances in Meteorology 7

(4) TWS changes retrieval based on spatiotemporal vari-ations of gravity field remains considerable uncer-tainty which includes errors produced in the removalof tidal movement and the mass migration becauseof the atmosphere and ocean circulation [11] as wellas the errors in hydrological models used for theestimation of other terrestrial water parameters [6]

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project was supported by National Natural ScienceFoundation of China (Grant no 51309210) and the ChineseAcademy of Sciences (Grant no KZZD-EW-08)

References

[1] Y Huang D Jiang D Zhuang Y Zhu and J Fu ldquoAn improvedapproach for modeling spatial distribution of water use profitmdasha case study in Tuhai Majia Basin Chinardquo Ecological Indicatorsvol 36 pp 94ndash99 2014

[2] Y-H Huang D Jiang D-F Zhuang J-H Wang H-J Yangand H-Y Ren ldquoEvaluation of relative water use efficiency(RWUE) at a regional scale a case study of Tuhai-Majia BasinChinardquo Water Science and Technology vol 66 no 5 pp 927ndash933 2012

[3] J S Famiglietti ldquoRemote sensing of terrestrial water storagesoil moisture and surface watersrdquo in The State of the PlanetFrontiers and Challenges in Geophysics R S J Sparks and C JHawkesworth Eds pp 197ndash207 2004

[4] B D Tapley S Bettadpur M Watkins and C Reigber ldquoThegravity recovery and climate experiment mission overview andearly resultsrdquo Geophysical Research Letters vol 31 no 9 ArticleID L09607 2004

[5] J Wahr S Swenson V Zlotnicki and I Velicogna ldquoTime-variable gravity from GRACE first resultsrdquo GeophysicalResearch Letters vol 31 no 11 Article ID L11501 2004

[6] A Guntner ldquoImprovement of global hydrological models usingGRACE datardquo Surveys in Geophysics vol 29 no 4-5 pp 375ndash397 2008

[7] G Ramillien J S Famiglietti and J Wahr ldquoDetection ofcontinental hydrology and glaciology Signals from GRACE areviewrdquo Surveys inGeophysics vol 29 no 4-5 pp 361ndash374 2008

[8] D P Chambers ldquoConverting 11 Release-04 Gravity Coefficientsinto Maps of Equivalent Water Thicknessrdquo 2007 httpgrace-tellusjplnasagovfilesGRACE-dpc200711 RL04pdf

[9] M Becker W LLovel A Cazenave A Guntner and J-FCretaux ldquoRecent hydrological behavior of the East Africangreat lakes region inferred from GRACE satellite altimetry andrainfall observationsrdquo Comptes Rendus Geoscience vol 342 no3 pp 223ndash233 2010

[10] X Hu J Chen Y Zhou C Huang and X Liao ldquoSeasonal waterstorage change of the Yangtze River basin detected by GracerdquoScience in China D vol 49 no 5 pp 483ndash491 2006

[11] J Wahr M Molenaar and F Bryan ldquoTime variability ofthe Earths gravity field hydrological and oceanic effects and

their possible detection using GRACErdquo Journal of GeophysicalResearch B vol 103 no 12 pp 30205ndash30229 1998

[12] M Rodell and J S Famiglietti ldquoDetectability of variations incontinental water storage from satellite observations of the timedependent gravity fieldrdquo Water Resources Research vol 35 no9 pp 2705ndash2723 1999

[13] M Rodell and J S Famiglietti ldquoAn analysis of terrestrial waterstorage variations in Illinois with implications for the GravityRecovery and Climate Experiment (GRACE)rdquoWater ResourcesResearch vol 37 no 5 pp 1327ndash1339 2001

[14] M Zhong J Duan H Xu P Peng H Yan and Y ZhuldquoTrend of China land water storage redistribution at medi-and large-spatial scales in recent five years by satellite gravityobservationsrdquo Chinese Science Bulletin vol 54 no 5 pp 816ndash821 2009

[15] H Wang L Jia H Steffen et al ldquoIncreased water storage inNorth America and Scandinavia from GRACE gravity datardquoNature Geoscience vol 6 no 1 pp 38ndash42 2013

[16] S C Swenson and P C D Milly ldquoClimate model biases inseasonally of continental water storage revealed by satellitegravimetryrdquoWater Resources Research vol 42 no 3 Article IDW03201 2006

[17] T H Syed J S FamigliettiM Rodell J Chen andC RWilsonldquoAnalysis of terrestrial water storage changes from GRACE andGLDASrdquo Water Resources Research vol 44 no 2 Article IDW02433 2008

[18] G-Y Niu and Z-L Yang ldquoAssessing a land surface modelsimprovements with GRACE estimatesrdquo Geophysical ResearchLetters vol 33 no 7 Article ID L07401 2006

[19] T Ngo-Duc K Laval G Ramillien J Polcher and A CazenaveldquoValidation of the land water storage simulated by OrganisingCarbon and Hydrology in Dynamic Ecosystems (ORCHIDEE)with Gravity Recovery and Climate Experiment (GRACE)datardquo Water Resources Research vol 43 no 4 Article IDW04427 2007

[20] J L Chen C R Wilson B D Tapley and J C Ries ldquoLowdegree gravitational changes from GRACE validation andinterpretationrdquo Geophysical Research Letters vol 31 no 22Article ID L22607 pp 1ndash5 2004

[21] R Klees E A Revtova B C Gunter et al ldquoThe design of anoptimal filter for monthly GRACE gravity modelsrdquo GeophysicalJournal International vol 175 no 2 pp 417ndash432 2008

[22] K-W Seo C R Wilson J S Famiglietti J L Chen andM Rodell ldquoTerrestrial water mass load changes from GravityRecovery and Climate Experiment (GRACE)rdquoWater ResourcesResearch vol 42 no 5 Article ID W05417 2006

[23] B D Tapley S Bettadpur J C Ries P F Thompson and MM Watkins ldquoGRACE measurements of mass variability in theEarth systemrdquo Science vol 305 no 5683 pp 503ndash505 2004

[24] D P Lettenmaier and J S Famiglietti ldquoHydrology water fromon highrdquo Nature vol 444 no 7119 pp 562ndash563 2006

[25] S Swenson P J-F Yeh J Wahr and J Famiglietti ldquoA compari-son of terrestrial water storage variations from GRACE with insitu measurements from Illinoisrdquo Geophysical Research Lettersvol 33 no 16 Article ID L16401 2006

[26] L Xavier M Becker A Cazenave L Longuevergne W Lloveland O C R Filho ldquoInterannual variability in water storageover 2003ndash2008 in the Amazon Basin from GRACE spacegravimetry in situ river level and precipitation datardquo RemoteSensing of Environment vol 114 no 8 pp 1629ndash1637 2010

8 Advances in Meteorology

[27] M Rodell and J S Famiglietti ldquoThe potential for satellite-basedmonitoring of groundwater storage changes using GRACE theHigh Plains aquifer Central USrdquo Journal of Hydrology vol 263no 1ndash4 pp 245ndash256 2002

[28] G Strassberg B R Scanlon and M Rodell ldquoComparison ofseasonal terrestrial water storage variations from GRACE withgroundwater-level measurements from the High Plains Aquifer(USA)rdquo Geophysical Research Letters vol 34 no 14 Article IDL14402 2007

[29] M Rodell I Velicogna and J S Famiglietti ldquoSatellite-basedestimates of groundwater depletion in Indiardquo Nature vol 460no 7258 pp 999ndash1002 2009

[30] X Lu and Q Zhuang ldquoEvaluating evapotranspiration andwater-use efficiency of terrestrial ecosystems in the contermi-nous United States using MODIS and AmeriFlux datardquo RemoteSensing of Environment vol 114 no 9 pp 1924ndash1939 2010

[31] M Rodell J S Famiglietti J Chen et al ldquoBasin scale estimatesof evapotranspiration using GRACE and other observationsrdquoGeophysical Research Letters vol 31 no 20 Article ID L205042004

[32] G Ramillien F Frappart AGuntner TNgo-DucA Cazenaveand K Laval ldquoTime variations of the regional evapotranspi-ration rate from Gravity Recovery and Climate Experiment(GRACE) satellite gravimetryrdquo Water Resources Research vol42 no 10 Article ID W10403 2006

[33] S Swenson and J Wahr ldquoEstimating large-scale precipitationminus evapotranspiration from GRACE satellite gravity mea-surementsrdquo Journal of Hydrometeorology vol 7 no 2 pp 252ndash270 2006

[34] M Leblanc P Tregoning G Ramillien S O Tweed andA Fakes ldquoBasin-scale integrated observations of the early21st century multiyear drought in southeast Australiardquo WaterResources Research vol 45 no 4 Article IDW04408 2009

[35] J L Chen C R Wilson B D Tapley Z L Yang and GY Niu ldquo2005 drought event in the Amazon River basin asmeasured byGRACE and estimated by climatemodelsrdquo Journalof Geophysical Research B vol 114 no 5 Article ID B054042009

[36] O B Andersen S I Seneviratne J Hinderer and P ViterboldquoGRACE-derived terrestrial water storage depletion associatedwith the 2003 European heat waverdquo Geophysical ResearchLetters vol 32 no 18 Article ID L18405 pp 1ndash4 2005

[37] F Frappart K Do Minh J LHermitte et al ldquoWater volumechange in the lower Mekong from satellite altimetry andimagery datardquo Geophysical Journal International vol 167 no 2pp 570ndash584 2006

[38] M D Wilson P Bates D Alsdorf et al ldquoModeling large-scale inundation of Amazonian seasonally flooded wetlandsrdquoGeophysical Research Letters vol 34 no 15 Article ID L154042007

[39] S-C Han C K Shum C Jekeli and D Alsdorf ldquoImprovedestimation of terrestrial water storage changes from GRACErdquoGeophysical Research Letters vol 32 no 7 Article ID L07302pp 1ndash5 2005

[40] B Wouters D Chambers and E J O Schrama ldquoGRACEobserves small-scale mass loss in Greenlandrdquo GeophysicalResearch Letters vol 35 no 20 Article ID L20501 2008

[41] I Velicogna and J Wahr ldquoMeasurements of time-variablegravity showmass loss in Antarcticardquo Science vol 311 no 5768pp 1754ndash1756 2006

[42] D C Slobbe P Ditmar and R C Lindenbergh ldquoEstimatingthe rates of mass change ice volume change and snow volume

change in Greenland from ICESat and GRACE datardquo Geophys-ical Journal International vol 176 no 1 pp 95ndash106 2009

[43] P L Svendsen O B Andersen and A A Nielsen ldquoAccelerationof the Greenland ice sheet mass loss as observed by GRACEconfidence and sensitivityrdquo Earth and Planetary Science Lettersvol 364 pp 24ndash29 2013

[44] A S Gardner G Moholdt B Wouters et al ldquoSharply increasedmass loss from glaciers and ice caps in the Canadian ArcticArchipelagordquo Nature vol 473 no 7347 pp 357ndash360 2011

[45] J L Chen B D Tapley and C R Wilson ldquoAlaskan mountainglacial melting observed by satellite gravimetryrdquo Earth andPlanetary Science Letters vol 248 no 1-2 pp 353ndash363 2006

[46] K Matsuo and K Heki ldquoTime-variable ice loss in Asianhigh mountains from satellite gravimetryrdquo Earth and PlanetaryScience Letters vol 290 no 1-2 pp 30ndash36 2010

[47] D Garcıa-Garcıa C C Ummenhofer and V Zlotnicki ldquoAus-tralian water mass variations fromGRACE data linked to Indo-Pacific climate variabilityrdquo Remote Sensing of Environment vol115 no 9 pp 2175ndash2183 2011

[48] W W Immerzeel L P H van Beek and M F P BierkensldquoClimate change will affect the asian water towersrdquo Science vol328 no 5984 pp 1382ndash1385 2010

[49] L S Soslashrensen S B Simonsen K Nielsen et al ldquoMass balanceof the Greenland ice sheet (2003ndash2008) from ICESat datamdashtheimpact of interpolation sampling and firn densityrdquo Cryospherevol 5 no 1 pp 173ndash186 2011

[50] W Zhang Y Wang and C Zhang ldquoThe preliminary analysisof effects of the soil moisture on gravity observationsrdquo Carto-graphica Sinica vol 30 no 2 pp 108ndash111 2001

[51] G Ramillien J S Famiglietti and J Wahr ldquoDetection ofcontinental hydrology and glaciology signals from GRACE areviewrdquo Surveys inGeophysics vol 29 no 4-5 pp 361ndash374 2008

[52] J L Chen C R Wilson R J Eanes and B D TapleyldquoGeophysical contributions to satellite nodal residual variationrdquoJournal of Geophysical Research B vol 104 no 10 pp 23237ndash23244 1999

[53] J K Willis D P Chambers and R S Nerem ldquoAssessing theglobally averaged sea level budget on seasonal to interannualtimescalesrdquo Journal of Geophysical Research C vol 113 no 6Article ID C06015 2008

[54] E W Leuliette and L Miller ldquoClosing the sea level rise budgetwith altimetry Argo and Gracerdquo Geophysical Research Lettersvol 36 no 4 Article ID L04608 2009

[55] J L Chen C RWilson J S Famiglietti andMRodell ldquoAttenu-ation effect on seasonal basin-scale water storage changes fromGRACE time-variable gravityrdquo Journal of Geodesy vol 81 no 4pp 237ndash245 2007

[56] G Zhu J Li HWen and JWang ldquoStudy on variations of globalcontinental water storage with GRACE gravity field modelsrdquoJournal of Geodesy and Geodynamics vol 28 no 5 pp 39ndash442008

[57] S Swenson and J Wahr ldquoMethods for inferring regionalsurface-mass anomalies from Gravity Recovery and ClimateExperiment (GRACE) measurements of time-variable gravityrdquoJournal of Geophysical Research B vol 107 no 9 pp 3-1ndash3-132002

[58] S Swenson and J Wahr ldquoMonitoring changes in continentalwater storage with gracerdquo Space Science Reviews vol 108 no1-2 pp 345ndash354 2003

[59] K-W Seo and C RWilson ldquoSimulated estimation of hydrolog-ical loads fromGRACErdquo Journal of Geodesy vol 78 no 7-8 pp442ndash456 2005

Advances in Meteorology 9

[60] S Swenson and J Wahr ldquoPost-processing removal of correlatederrors in GRACE datardquoGeophysical Research Letters vol 33 no8 Article ID L08402 2006

[61] G Ramillien F Frappart A Cazenave and A Guntner ldquoTimevariations of land water storage from an inversion of 2 years ofGRACE geoidsrdquo Earth and Planetary Science Letters vol 235no 1-2 pp 283ndash301 2005

[62] F Frederic G Ramillien M Leblanc et al ldquoAn independentcomponent analysis filtering approach for estimating continen-tal hydrology in the GRACE gravity datardquo Remote Sensing ofEnvironment vol 115 no 1 pp 187ndash204 2011

[63] S Werth A Guntner R Schmidt and J Kusche ldquoEvaluation ofGRACE filter tools from a hydrological perspectiverdquo Geophysi-cal Journal International vol 179 no 3 pp 1499ndash1515 2009

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Applied ampEnvironmentalSoil Science

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International Journal of

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OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Advances in Meteorology 5

of GRACE gravity field data to TWS changes which are allimportant in TWS retrieval improvement

(3) Further Combination of GRACE Data with Associ-ated Hydrological Models For GRACE-based TWS changesretrieval does not involve the hydrological mechanisms it isnecessary to complement GRACE-based TWS by hydrologi-cal models for furthering its application in terrestrial hydrol-ogy monitoring Further combination of GRACE and hydro-logical models needs resolving their consistencies of spacetime and component Spatial consistency can be solvedby adjusting the calculation unit of hydrological models toreflect the spatial variability (such as distributed hydrologicalmodels) Temporal consistency requires analysis of upscalingGRACE data and downscaling hydrological models simula-tion Component consistency can be achieved by GRACE-based TWS signals subdivision or revising parameters ofhydrological models to TWS Through space time andcomponent consistency improvement the gravity field dataandmeasured data together can become basic dataset to forcehydrological models in the future

Appendices

A Water Storage Change Retrieval

Thechanges in terrestrial water storage result inmass redistri-bution in the Earthrsquos system thereby causing changes in thegravity field For a fixed continental region the changes inwater storage (including soil water and surface snow) comefrom rainfall evapotranspiration river transportation anddeep underground infiltration Except the rainfall which cancause increased water storage the remaining three processesall reduce it [10] Using the FG5 absolute gravimeter Zhanget al [50] measured the gravity change of nearly 10minus7msdotsminus2 attheWuhanUniversity site before and after a rainstorm whichclearly shows the influence of terrestrial water variation ongravity The Earthrsquos gravity field can be expressed as geoid

119873(120579 120582)

= 119886

infin

sum

119899=0

119899

sum

119898=0

[119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A1)

where 119899 and 119898 are harmonic degree and order of the gravityfield respectively 119886 is the Earthrsquos equatorial radius (about6371 km) 120579 and 120582 are colatitudes (the difference between90∘ and latitude) and longitude 119862

119899119898and 119878

119899119898are spherical

harmonic coefficients (dimensionless)119875119899119898

is the normalizedassociated Legendre functions The maximum value 119873 ofthe order 119899 of ideal gravity field should be infinite (119873 sim

infin) while the actual order of spherical harmonic coefficientsobtained by the gravity satellite has a finite value (119873 lt infin)and the spatial resolution of gravity field data is estimatedapproximately to be 120587119886119873 [51] Geoid height changes Δ119873

caused by the movement of substances on the Earthrsquos surfacecan be expressed as

Δ119873 (120579 120582)

= 119886

infin

sum

119899=0

119899

sum

119898=0

[Δ119862

119899119898cos (119898120582) + Δ119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A2)

where Δ119862119899119898

and Δ119878119899119898

are the changes of 119899-degree 119898-orderspherical harmonic coefficients of geoid and can be expressedas [5 52]

Δ119862

119899119898

Δ119878

119899119898

=

3

4120587119886120588

119886(2119899 + 1)

timesintΔ120588 (119903 120579 120582) 119875

119899119898(cos 120579)( 119903

119886

)

119899+2

cos (119898120582)sin (119898120582) sin 120579119889120579 119889120582 119889119903

(A3)

where 120588119886is the average density of the Earth (5517 kgm3)

and Δ120588(119903 120579 120582) is the change of bulk density at a particularlocation In gravity field inversion because the height changeof substances on the Earthrsquos surface 119867 is relatively smallcompared to the Earthrsquos average radius 119886 in gravity fieldretrieval ((119903119886) asymp 1) the changes of the gravity field directlycaused by the surface mass can be expressed as

Δ119862

119899119898

Δ119878

119899119898

surf

=

3

4120587119886120588

119886(2119899 + 1)

times intΔ120590 (120579 120582) 119875

119899119898(cos 120579) cos (119898120582)sin (119898120582) sin 120579119889120579 119889120582

(A4)

where Δ120590 is surface density change Δ120590 = intΔ120588(119903 120579 120582)119889119903Furthermore the surface mass variation in loads will causedeformation to the solid Earth which in turn can indirectlycause variations to the gravity field This can be expressed as[5 52]

Δ119862

119899119898

Δ119878

119899119898

soild

=

3119896

1015840

119899

4120587119886120588

119886(2119899 + 1)

times intΔ120590 (120579 120582) 119875

119899119898(cos 120579) cos (119898120582)sin (119898120582) sin 120579119889120579 119889120582

(A5)

where 119896

1015840

119899is load LOVE number of coefficients and the

specific value of 1198961015840119899can be found in relevant literature [11]

6 Advances in Meteorology

Thus the change of the Earthrsquos gravity field caused by massvariations on the Earthrsquos surface is given by

Δ119862

119899119898

Δ119878

119899119898

=

Δ119862

119899119898

Δ119878

119899119898

surf

+

Δ119862

119899119898

Δ119878

119899119898

soild

= (1 + 119896

1015840

119899)

Δ119862

119899119898

Δ119878

119899119898

surf

(A6)

If the spherical harmonic expansion is performed on thesurface density change Δ120590 then

Δ120590 (120579 120582)

= 119886120588

119908

infin

sum

119899=0

119899

sum

119898=0

[

119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A7)

where 120588119908is the density of water andΔ120590120588

119908can be considered

as mass variation on the Earthrsquos surface expressed in waterequivalent height Wahr et al [5] proposed that

Δ

119862

119899119898

Δ

119878

119899119898

=

120588

119886

3120588

119908

2119899 + 1

1 + 119896

1015840

119899

Δ119862

119899119898

Δ119878

119899119898

(A8)

The surface density changeΔ120590 can be calculated using thefollowing equation

Δ120590 (120579 120582)

=

119886120588

119886

3

infin

sum

119899=0

119899

sum

119898=0

2119899 + 1

1 + 119896

1015840

119899

[119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)]

times 119875

119899119898(cos 120579)

(A9)

For ocean and atmosphere mass variations are removedbased on Parallel Ocean Program (POP) model the aboveequation is the basic equation for the retrieval of surfacemassvariations based on spatiotemporal changes gravity fieldThe Earthrsquos surface density changes can be derived from thechanges of gravity field coefficients obtained from GRACEsatellites

B Evaluation Errors

Currently the latest available GRACE dataset product is theRL05 The accuracy of data provided by CSR and GFZ isbetter than that provided by JPL The evaluation errors ofGRACE are brought from satellite instrumentsmeasurementretrieval models and other factors as follows

(1) Gravity field data measured by GRACE satellite maybe contaminated by satellite measurement errors forthe influence of satellite orbit satellite K-band rang-ing and accelerometer measurement [20] The satel-lite measurement errors also include poor accuracyof C20 due to the insensitivity of track geometry to

the gravity fieldrsquos low degree gravitational variations[5 20] It is generally releasedwith removing variationof C20 [10] or replacing it by satellite laser ranging(SLR) substitution [20] In addition the missing offirst-degree spherical harmonic coefficients will alsobring error to GRACE It can commonly be resolvedby substituting value calculated from the term of theseasonal changes of the Earthrsquos mass center [53 54] orignoring its impact [55]

(2) In theory the retrieval of gravity field variation needsto use spherical harmonic coefficients of all degreesfrom 0 to infinity However gravity satellites can onlyprovide definite order data So the surface densitychange Δ120590 in retrieval models is treated by sphericalharmonic expansion to definite orders For the impactof high-order terms on the Earthrsquos surface densitychange Δ120590 cannot be ignored it results in truncationerrors in gravity field retrieval RL05 water storagedata is estimated by CSR using a retrieval modeltruncated to degree 60 [8] Zhu et al (2008) comparedthe global water storage retrieval results using modelstruncated to 15 degrees 20 degrees 35 degrees and60 degrees [56]They found that although some infor-mation of TWS change may be missing the retrievalresult of TWS change became more marked withlower truncation degree Generally the water storageretrieval truncated to order 60 is widely adopted [17]

(3) For terrestrial water monitoring focusing on themass changes of a particular area (eg river basin)it requires the integral process on density changeΔ120590 = ((intΔ120590(120579 120582)119906(120579 120582)119889Ω)Ω) The function ofregional characteristics 119906(120579 120582) is equal to 1 insidethe particular area and to zero outside The errorwill be brought for the discontinuity of 119906(120579 120582) in thedomain of integration In addition for the influenceof rapid increase of the errors of GRACE gravityfield model coefficients with increase of sphericalharmonic coefficients degree signal leakage errorsand the striping pollution [23] filtering methods areproposed to smooth GRACE data for noise reducingwhich will result in filtering errors of retrieval resultsProposed filtering methods include spatial averagingsymmetric Gaussian filtering optimized decorrela-tion filtering time-series method global hydrolog-ical model correction method kernel-independentcomponent analysis and optimal smoothing kernelmethod [53 57ndash62] Using filtering for the integraltreatment of surface density changes can effectivelyremove the striping to a certain extent Howeverthe obtained average surface density is critical for itreduces the useful energy of geophysical signals andresults in filtering errors In addition the existingfiltering methods require the support of a prioriknowledge (such as filtering radius and truncationdegree) Therefore in the actual retrieval process thefilter selection and parameter calibration require anunderstanding of the specific regional characteristics[60 63]

Advances in Meteorology 7

(4) TWS changes retrieval based on spatiotemporal vari-ations of gravity field remains considerable uncer-tainty which includes errors produced in the removalof tidal movement and the mass migration becauseof the atmosphere and ocean circulation [11] as wellas the errors in hydrological models used for theestimation of other terrestrial water parameters [6]

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project was supported by National Natural ScienceFoundation of China (Grant no 51309210) and the ChineseAcademy of Sciences (Grant no KZZD-EW-08)

References

[1] Y Huang D Jiang D Zhuang Y Zhu and J Fu ldquoAn improvedapproach for modeling spatial distribution of water use profitmdasha case study in Tuhai Majia Basin Chinardquo Ecological Indicatorsvol 36 pp 94ndash99 2014

[2] Y-H Huang D Jiang D-F Zhuang J-H Wang H-J Yangand H-Y Ren ldquoEvaluation of relative water use efficiency(RWUE) at a regional scale a case study of Tuhai-Majia BasinChinardquo Water Science and Technology vol 66 no 5 pp 927ndash933 2012

[3] J S Famiglietti ldquoRemote sensing of terrestrial water storagesoil moisture and surface watersrdquo in The State of the PlanetFrontiers and Challenges in Geophysics R S J Sparks and C JHawkesworth Eds pp 197ndash207 2004

[4] B D Tapley S Bettadpur M Watkins and C Reigber ldquoThegravity recovery and climate experiment mission overview andearly resultsrdquo Geophysical Research Letters vol 31 no 9 ArticleID L09607 2004

[5] J Wahr S Swenson V Zlotnicki and I Velicogna ldquoTime-variable gravity from GRACE first resultsrdquo GeophysicalResearch Letters vol 31 no 11 Article ID L11501 2004

[6] A Guntner ldquoImprovement of global hydrological models usingGRACE datardquo Surveys in Geophysics vol 29 no 4-5 pp 375ndash397 2008

[7] G Ramillien J S Famiglietti and J Wahr ldquoDetection ofcontinental hydrology and glaciology Signals from GRACE areviewrdquo Surveys inGeophysics vol 29 no 4-5 pp 361ndash374 2008

[8] D P Chambers ldquoConverting 11 Release-04 Gravity Coefficientsinto Maps of Equivalent Water Thicknessrdquo 2007 httpgrace-tellusjplnasagovfilesGRACE-dpc200711 RL04pdf

[9] M Becker W LLovel A Cazenave A Guntner and J-FCretaux ldquoRecent hydrological behavior of the East Africangreat lakes region inferred from GRACE satellite altimetry andrainfall observationsrdquo Comptes Rendus Geoscience vol 342 no3 pp 223ndash233 2010

[10] X Hu J Chen Y Zhou C Huang and X Liao ldquoSeasonal waterstorage change of the Yangtze River basin detected by GracerdquoScience in China D vol 49 no 5 pp 483ndash491 2006

[11] J Wahr M Molenaar and F Bryan ldquoTime variability ofthe Earths gravity field hydrological and oceanic effects and

their possible detection using GRACErdquo Journal of GeophysicalResearch B vol 103 no 12 pp 30205ndash30229 1998

[12] M Rodell and J S Famiglietti ldquoDetectability of variations incontinental water storage from satellite observations of the timedependent gravity fieldrdquo Water Resources Research vol 35 no9 pp 2705ndash2723 1999

[13] M Rodell and J S Famiglietti ldquoAn analysis of terrestrial waterstorage variations in Illinois with implications for the GravityRecovery and Climate Experiment (GRACE)rdquoWater ResourcesResearch vol 37 no 5 pp 1327ndash1339 2001

[14] M Zhong J Duan H Xu P Peng H Yan and Y ZhuldquoTrend of China land water storage redistribution at medi-and large-spatial scales in recent five years by satellite gravityobservationsrdquo Chinese Science Bulletin vol 54 no 5 pp 816ndash821 2009

[15] H Wang L Jia H Steffen et al ldquoIncreased water storage inNorth America and Scandinavia from GRACE gravity datardquoNature Geoscience vol 6 no 1 pp 38ndash42 2013

[16] S C Swenson and P C D Milly ldquoClimate model biases inseasonally of continental water storage revealed by satellitegravimetryrdquoWater Resources Research vol 42 no 3 Article IDW03201 2006

[17] T H Syed J S FamigliettiM Rodell J Chen andC RWilsonldquoAnalysis of terrestrial water storage changes from GRACE andGLDASrdquo Water Resources Research vol 44 no 2 Article IDW02433 2008

[18] G-Y Niu and Z-L Yang ldquoAssessing a land surface modelsimprovements with GRACE estimatesrdquo Geophysical ResearchLetters vol 33 no 7 Article ID L07401 2006

[19] T Ngo-Duc K Laval G Ramillien J Polcher and A CazenaveldquoValidation of the land water storage simulated by OrganisingCarbon and Hydrology in Dynamic Ecosystems (ORCHIDEE)with Gravity Recovery and Climate Experiment (GRACE)datardquo Water Resources Research vol 43 no 4 Article IDW04427 2007

[20] J L Chen C R Wilson B D Tapley and J C Ries ldquoLowdegree gravitational changes from GRACE validation andinterpretationrdquo Geophysical Research Letters vol 31 no 22Article ID L22607 pp 1ndash5 2004

[21] R Klees E A Revtova B C Gunter et al ldquoThe design of anoptimal filter for monthly GRACE gravity modelsrdquo GeophysicalJournal International vol 175 no 2 pp 417ndash432 2008

[22] K-W Seo C R Wilson J S Famiglietti J L Chen andM Rodell ldquoTerrestrial water mass load changes from GravityRecovery and Climate Experiment (GRACE)rdquoWater ResourcesResearch vol 42 no 5 Article ID W05417 2006

[23] B D Tapley S Bettadpur J C Ries P F Thompson and MM Watkins ldquoGRACE measurements of mass variability in theEarth systemrdquo Science vol 305 no 5683 pp 503ndash505 2004

[24] D P Lettenmaier and J S Famiglietti ldquoHydrology water fromon highrdquo Nature vol 444 no 7119 pp 562ndash563 2006

[25] S Swenson P J-F Yeh J Wahr and J Famiglietti ldquoA compari-son of terrestrial water storage variations from GRACE with insitu measurements from Illinoisrdquo Geophysical Research Lettersvol 33 no 16 Article ID L16401 2006

[26] L Xavier M Becker A Cazenave L Longuevergne W Lloveland O C R Filho ldquoInterannual variability in water storageover 2003ndash2008 in the Amazon Basin from GRACE spacegravimetry in situ river level and precipitation datardquo RemoteSensing of Environment vol 114 no 8 pp 1629ndash1637 2010

8 Advances in Meteorology

[27] M Rodell and J S Famiglietti ldquoThe potential for satellite-basedmonitoring of groundwater storage changes using GRACE theHigh Plains aquifer Central USrdquo Journal of Hydrology vol 263no 1ndash4 pp 245ndash256 2002

[28] G Strassberg B R Scanlon and M Rodell ldquoComparison ofseasonal terrestrial water storage variations from GRACE withgroundwater-level measurements from the High Plains Aquifer(USA)rdquo Geophysical Research Letters vol 34 no 14 Article IDL14402 2007

[29] M Rodell I Velicogna and J S Famiglietti ldquoSatellite-basedestimates of groundwater depletion in Indiardquo Nature vol 460no 7258 pp 999ndash1002 2009

[30] X Lu and Q Zhuang ldquoEvaluating evapotranspiration andwater-use efficiency of terrestrial ecosystems in the contermi-nous United States using MODIS and AmeriFlux datardquo RemoteSensing of Environment vol 114 no 9 pp 1924ndash1939 2010

[31] M Rodell J S Famiglietti J Chen et al ldquoBasin scale estimatesof evapotranspiration using GRACE and other observationsrdquoGeophysical Research Letters vol 31 no 20 Article ID L205042004

[32] G Ramillien F Frappart AGuntner TNgo-DucA Cazenaveand K Laval ldquoTime variations of the regional evapotranspi-ration rate from Gravity Recovery and Climate Experiment(GRACE) satellite gravimetryrdquo Water Resources Research vol42 no 10 Article ID W10403 2006

[33] S Swenson and J Wahr ldquoEstimating large-scale precipitationminus evapotranspiration from GRACE satellite gravity mea-surementsrdquo Journal of Hydrometeorology vol 7 no 2 pp 252ndash270 2006

[34] M Leblanc P Tregoning G Ramillien S O Tweed andA Fakes ldquoBasin-scale integrated observations of the early21st century multiyear drought in southeast Australiardquo WaterResources Research vol 45 no 4 Article IDW04408 2009

[35] J L Chen C R Wilson B D Tapley Z L Yang and GY Niu ldquo2005 drought event in the Amazon River basin asmeasured byGRACE and estimated by climatemodelsrdquo Journalof Geophysical Research B vol 114 no 5 Article ID B054042009

[36] O B Andersen S I Seneviratne J Hinderer and P ViterboldquoGRACE-derived terrestrial water storage depletion associatedwith the 2003 European heat waverdquo Geophysical ResearchLetters vol 32 no 18 Article ID L18405 pp 1ndash4 2005

[37] F Frappart K Do Minh J LHermitte et al ldquoWater volumechange in the lower Mekong from satellite altimetry andimagery datardquo Geophysical Journal International vol 167 no 2pp 570ndash584 2006

[38] M D Wilson P Bates D Alsdorf et al ldquoModeling large-scale inundation of Amazonian seasonally flooded wetlandsrdquoGeophysical Research Letters vol 34 no 15 Article ID L154042007

[39] S-C Han C K Shum C Jekeli and D Alsdorf ldquoImprovedestimation of terrestrial water storage changes from GRACErdquoGeophysical Research Letters vol 32 no 7 Article ID L07302pp 1ndash5 2005

[40] B Wouters D Chambers and E J O Schrama ldquoGRACEobserves small-scale mass loss in Greenlandrdquo GeophysicalResearch Letters vol 35 no 20 Article ID L20501 2008

[41] I Velicogna and J Wahr ldquoMeasurements of time-variablegravity showmass loss in Antarcticardquo Science vol 311 no 5768pp 1754ndash1756 2006

[42] D C Slobbe P Ditmar and R C Lindenbergh ldquoEstimatingthe rates of mass change ice volume change and snow volume

change in Greenland from ICESat and GRACE datardquo Geophys-ical Journal International vol 176 no 1 pp 95ndash106 2009

[43] P L Svendsen O B Andersen and A A Nielsen ldquoAccelerationof the Greenland ice sheet mass loss as observed by GRACEconfidence and sensitivityrdquo Earth and Planetary Science Lettersvol 364 pp 24ndash29 2013

[44] A S Gardner G Moholdt B Wouters et al ldquoSharply increasedmass loss from glaciers and ice caps in the Canadian ArcticArchipelagordquo Nature vol 473 no 7347 pp 357ndash360 2011

[45] J L Chen B D Tapley and C R Wilson ldquoAlaskan mountainglacial melting observed by satellite gravimetryrdquo Earth andPlanetary Science Letters vol 248 no 1-2 pp 353ndash363 2006

[46] K Matsuo and K Heki ldquoTime-variable ice loss in Asianhigh mountains from satellite gravimetryrdquo Earth and PlanetaryScience Letters vol 290 no 1-2 pp 30ndash36 2010

[47] D Garcıa-Garcıa C C Ummenhofer and V Zlotnicki ldquoAus-tralian water mass variations fromGRACE data linked to Indo-Pacific climate variabilityrdquo Remote Sensing of Environment vol115 no 9 pp 2175ndash2183 2011

[48] W W Immerzeel L P H van Beek and M F P BierkensldquoClimate change will affect the asian water towersrdquo Science vol328 no 5984 pp 1382ndash1385 2010

[49] L S Soslashrensen S B Simonsen K Nielsen et al ldquoMass balanceof the Greenland ice sheet (2003ndash2008) from ICESat datamdashtheimpact of interpolation sampling and firn densityrdquo Cryospherevol 5 no 1 pp 173ndash186 2011

[50] W Zhang Y Wang and C Zhang ldquoThe preliminary analysisof effects of the soil moisture on gravity observationsrdquo Carto-graphica Sinica vol 30 no 2 pp 108ndash111 2001

[51] G Ramillien J S Famiglietti and J Wahr ldquoDetection ofcontinental hydrology and glaciology signals from GRACE areviewrdquo Surveys inGeophysics vol 29 no 4-5 pp 361ndash374 2008

[52] J L Chen C R Wilson R J Eanes and B D TapleyldquoGeophysical contributions to satellite nodal residual variationrdquoJournal of Geophysical Research B vol 104 no 10 pp 23237ndash23244 1999

[53] J K Willis D P Chambers and R S Nerem ldquoAssessing theglobally averaged sea level budget on seasonal to interannualtimescalesrdquo Journal of Geophysical Research C vol 113 no 6Article ID C06015 2008

[54] E W Leuliette and L Miller ldquoClosing the sea level rise budgetwith altimetry Argo and Gracerdquo Geophysical Research Lettersvol 36 no 4 Article ID L04608 2009

[55] J L Chen C RWilson J S Famiglietti andMRodell ldquoAttenu-ation effect on seasonal basin-scale water storage changes fromGRACE time-variable gravityrdquo Journal of Geodesy vol 81 no 4pp 237ndash245 2007

[56] G Zhu J Li HWen and JWang ldquoStudy on variations of globalcontinental water storage with GRACE gravity field modelsrdquoJournal of Geodesy and Geodynamics vol 28 no 5 pp 39ndash442008

[57] S Swenson and J Wahr ldquoMethods for inferring regionalsurface-mass anomalies from Gravity Recovery and ClimateExperiment (GRACE) measurements of time-variable gravityrdquoJournal of Geophysical Research B vol 107 no 9 pp 3-1ndash3-132002

[58] S Swenson and J Wahr ldquoMonitoring changes in continentalwater storage with gracerdquo Space Science Reviews vol 108 no1-2 pp 345ndash354 2003

[59] K-W Seo and C RWilson ldquoSimulated estimation of hydrolog-ical loads fromGRACErdquo Journal of Geodesy vol 78 no 7-8 pp442ndash456 2005

Advances in Meteorology 9

[60] S Swenson and J Wahr ldquoPost-processing removal of correlatederrors in GRACE datardquoGeophysical Research Letters vol 33 no8 Article ID L08402 2006

[61] G Ramillien F Frappart A Cazenave and A Guntner ldquoTimevariations of land water storage from an inversion of 2 years ofGRACE geoidsrdquo Earth and Planetary Science Letters vol 235no 1-2 pp 283ndash301 2005

[62] F Frederic G Ramillien M Leblanc et al ldquoAn independentcomponent analysis filtering approach for estimating continen-tal hydrology in the GRACE gravity datardquo Remote Sensing ofEnvironment vol 115 no 1 pp 187ndash204 2011

[63] S Werth A Guntner R Schmidt and J Kusche ldquoEvaluation ofGRACE filter tools from a hydrological perspectiverdquo Geophysi-cal Journal International vol 179 no 3 pp 1499ndash1515 2009

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

6 Advances in Meteorology

Thus the change of the Earthrsquos gravity field caused by massvariations on the Earthrsquos surface is given by

Δ119862

119899119898

Δ119878

119899119898

=

Δ119862

119899119898

Δ119878

119899119898

surf

+

Δ119862

119899119898

Δ119878

119899119898

soild

= (1 + 119896

1015840

119899)

Δ119862

119899119898

Δ119878

119899119898

surf

(A6)

If the spherical harmonic expansion is performed on thesurface density change Δ120590 then

Δ120590 (120579 120582)

= 119886120588

119908

infin

sum

119899=0

119899

sum

119898=0

[

119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)] 119875

119899119898(cos 120579)

(A7)

where 120588119908is the density of water andΔ120590120588

119908can be considered

as mass variation on the Earthrsquos surface expressed in waterequivalent height Wahr et al [5] proposed that

Δ

119862

119899119898

Δ

119878

119899119898

=

120588

119886

3120588

119908

2119899 + 1

1 + 119896

1015840

119899

Δ119862

119899119898

Δ119878

119899119898

(A8)

The surface density changeΔ120590 can be calculated using thefollowing equation

Δ120590 (120579 120582)

=

119886120588

119886

3

infin

sum

119899=0

119899

sum

119898=0

2119899 + 1

1 + 119896

1015840

119899

[119862

119899119898cos (119898120582) + 119878

119899119898sin (119898120582)]

times 119875

119899119898(cos 120579)

(A9)

For ocean and atmosphere mass variations are removedbased on Parallel Ocean Program (POP) model the aboveequation is the basic equation for the retrieval of surfacemassvariations based on spatiotemporal changes gravity fieldThe Earthrsquos surface density changes can be derived from thechanges of gravity field coefficients obtained from GRACEsatellites

B Evaluation Errors

Currently the latest available GRACE dataset product is theRL05 The accuracy of data provided by CSR and GFZ isbetter than that provided by JPL The evaluation errors ofGRACE are brought from satellite instrumentsmeasurementretrieval models and other factors as follows

(1) Gravity field data measured by GRACE satellite maybe contaminated by satellite measurement errors forthe influence of satellite orbit satellite K-band rang-ing and accelerometer measurement [20] The satel-lite measurement errors also include poor accuracyof C20 due to the insensitivity of track geometry to

the gravity fieldrsquos low degree gravitational variations[5 20] It is generally releasedwith removing variationof C20 [10] or replacing it by satellite laser ranging(SLR) substitution [20] In addition the missing offirst-degree spherical harmonic coefficients will alsobring error to GRACE It can commonly be resolvedby substituting value calculated from the term of theseasonal changes of the Earthrsquos mass center [53 54] orignoring its impact [55]

(2) In theory the retrieval of gravity field variation needsto use spherical harmonic coefficients of all degreesfrom 0 to infinity However gravity satellites can onlyprovide definite order data So the surface densitychange Δ120590 in retrieval models is treated by sphericalharmonic expansion to definite orders For the impactof high-order terms on the Earthrsquos surface densitychange Δ120590 cannot be ignored it results in truncationerrors in gravity field retrieval RL05 water storagedata is estimated by CSR using a retrieval modeltruncated to degree 60 [8] Zhu et al (2008) comparedthe global water storage retrieval results using modelstruncated to 15 degrees 20 degrees 35 degrees and60 degrees [56]They found that although some infor-mation of TWS change may be missing the retrievalresult of TWS change became more marked withlower truncation degree Generally the water storageretrieval truncated to order 60 is widely adopted [17]

(3) For terrestrial water monitoring focusing on themass changes of a particular area (eg river basin)it requires the integral process on density changeΔ120590 = ((intΔ120590(120579 120582)119906(120579 120582)119889Ω)Ω) The function ofregional characteristics 119906(120579 120582) is equal to 1 insidethe particular area and to zero outside The errorwill be brought for the discontinuity of 119906(120579 120582) in thedomain of integration In addition for the influenceof rapid increase of the errors of GRACE gravityfield model coefficients with increase of sphericalharmonic coefficients degree signal leakage errorsand the striping pollution [23] filtering methods areproposed to smooth GRACE data for noise reducingwhich will result in filtering errors of retrieval resultsProposed filtering methods include spatial averagingsymmetric Gaussian filtering optimized decorrela-tion filtering time-series method global hydrolog-ical model correction method kernel-independentcomponent analysis and optimal smoothing kernelmethod [53 57ndash62] Using filtering for the integraltreatment of surface density changes can effectivelyremove the striping to a certain extent Howeverthe obtained average surface density is critical for itreduces the useful energy of geophysical signals andresults in filtering errors In addition the existingfiltering methods require the support of a prioriknowledge (such as filtering radius and truncationdegree) Therefore in the actual retrieval process thefilter selection and parameter calibration require anunderstanding of the specific regional characteristics[60 63]

Advances in Meteorology 7

(4) TWS changes retrieval based on spatiotemporal vari-ations of gravity field remains considerable uncer-tainty which includes errors produced in the removalof tidal movement and the mass migration becauseof the atmosphere and ocean circulation [11] as wellas the errors in hydrological models used for theestimation of other terrestrial water parameters [6]

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project was supported by National Natural ScienceFoundation of China (Grant no 51309210) and the ChineseAcademy of Sciences (Grant no KZZD-EW-08)

References

[1] Y Huang D Jiang D Zhuang Y Zhu and J Fu ldquoAn improvedapproach for modeling spatial distribution of water use profitmdasha case study in Tuhai Majia Basin Chinardquo Ecological Indicatorsvol 36 pp 94ndash99 2014

[2] Y-H Huang D Jiang D-F Zhuang J-H Wang H-J Yangand H-Y Ren ldquoEvaluation of relative water use efficiency(RWUE) at a regional scale a case study of Tuhai-Majia BasinChinardquo Water Science and Technology vol 66 no 5 pp 927ndash933 2012

[3] J S Famiglietti ldquoRemote sensing of terrestrial water storagesoil moisture and surface watersrdquo in The State of the PlanetFrontiers and Challenges in Geophysics R S J Sparks and C JHawkesworth Eds pp 197ndash207 2004

[4] B D Tapley S Bettadpur M Watkins and C Reigber ldquoThegravity recovery and climate experiment mission overview andearly resultsrdquo Geophysical Research Letters vol 31 no 9 ArticleID L09607 2004

[5] J Wahr S Swenson V Zlotnicki and I Velicogna ldquoTime-variable gravity from GRACE first resultsrdquo GeophysicalResearch Letters vol 31 no 11 Article ID L11501 2004

[6] A Guntner ldquoImprovement of global hydrological models usingGRACE datardquo Surveys in Geophysics vol 29 no 4-5 pp 375ndash397 2008

[7] G Ramillien J S Famiglietti and J Wahr ldquoDetection ofcontinental hydrology and glaciology Signals from GRACE areviewrdquo Surveys inGeophysics vol 29 no 4-5 pp 361ndash374 2008

[8] D P Chambers ldquoConverting 11 Release-04 Gravity Coefficientsinto Maps of Equivalent Water Thicknessrdquo 2007 httpgrace-tellusjplnasagovfilesGRACE-dpc200711 RL04pdf

[9] M Becker W LLovel A Cazenave A Guntner and J-FCretaux ldquoRecent hydrological behavior of the East Africangreat lakes region inferred from GRACE satellite altimetry andrainfall observationsrdquo Comptes Rendus Geoscience vol 342 no3 pp 223ndash233 2010

[10] X Hu J Chen Y Zhou C Huang and X Liao ldquoSeasonal waterstorage change of the Yangtze River basin detected by GracerdquoScience in China D vol 49 no 5 pp 483ndash491 2006

[11] J Wahr M Molenaar and F Bryan ldquoTime variability ofthe Earths gravity field hydrological and oceanic effects and

their possible detection using GRACErdquo Journal of GeophysicalResearch B vol 103 no 12 pp 30205ndash30229 1998

[12] M Rodell and J S Famiglietti ldquoDetectability of variations incontinental water storage from satellite observations of the timedependent gravity fieldrdquo Water Resources Research vol 35 no9 pp 2705ndash2723 1999

[13] M Rodell and J S Famiglietti ldquoAn analysis of terrestrial waterstorage variations in Illinois with implications for the GravityRecovery and Climate Experiment (GRACE)rdquoWater ResourcesResearch vol 37 no 5 pp 1327ndash1339 2001

[14] M Zhong J Duan H Xu P Peng H Yan and Y ZhuldquoTrend of China land water storage redistribution at medi-and large-spatial scales in recent five years by satellite gravityobservationsrdquo Chinese Science Bulletin vol 54 no 5 pp 816ndash821 2009

[15] H Wang L Jia H Steffen et al ldquoIncreased water storage inNorth America and Scandinavia from GRACE gravity datardquoNature Geoscience vol 6 no 1 pp 38ndash42 2013

[16] S C Swenson and P C D Milly ldquoClimate model biases inseasonally of continental water storage revealed by satellitegravimetryrdquoWater Resources Research vol 42 no 3 Article IDW03201 2006

[17] T H Syed J S FamigliettiM Rodell J Chen andC RWilsonldquoAnalysis of terrestrial water storage changes from GRACE andGLDASrdquo Water Resources Research vol 44 no 2 Article IDW02433 2008

[18] G-Y Niu and Z-L Yang ldquoAssessing a land surface modelsimprovements with GRACE estimatesrdquo Geophysical ResearchLetters vol 33 no 7 Article ID L07401 2006

[19] T Ngo-Duc K Laval G Ramillien J Polcher and A CazenaveldquoValidation of the land water storage simulated by OrganisingCarbon and Hydrology in Dynamic Ecosystems (ORCHIDEE)with Gravity Recovery and Climate Experiment (GRACE)datardquo Water Resources Research vol 43 no 4 Article IDW04427 2007

[20] J L Chen C R Wilson B D Tapley and J C Ries ldquoLowdegree gravitational changes from GRACE validation andinterpretationrdquo Geophysical Research Letters vol 31 no 22Article ID L22607 pp 1ndash5 2004

[21] R Klees E A Revtova B C Gunter et al ldquoThe design of anoptimal filter for monthly GRACE gravity modelsrdquo GeophysicalJournal International vol 175 no 2 pp 417ndash432 2008

[22] K-W Seo C R Wilson J S Famiglietti J L Chen andM Rodell ldquoTerrestrial water mass load changes from GravityRecovery and Climate Experiment (GRACE)rdquoWater ResourcesResearch vol 42 no 5 Article ID W05417 2006

[23] B D Tapley S Bettadpur J C Ries P F Thompson and MM Watkins ldquoGRACE measurements of mass variability in theEarth systemrdquo Science vol 305 no 5683 pp 503ndash505 2004

[24] D P Lettenmaier and J S Famiglietti ldquoHydrology water fromon highrdquo Nature vol 444 no 7119 pp 562ndash563 2006

[25] S Swenson P J-F Yeh J Wahr and J Famiglietti ldquoA compari-son of terrestrial water storage variations from GRACE with insitu measurements from Illinoisrdquo Geophysical Research Lettersvol 33 no 16 Article ID L16401 2006

[26] L Xavier M Becker A Cazenave L Longuevergne W Lloveland O C R Filho ldquoInterannual variability in water storageover 2003ndash2008 in the Amazon Basin from GRACE spacegravimetry in situ river level and precipitation datardquo RemoteSensing of Environment vol 114 no 8 pp 1629ndash1637 2010

8 Advances in Meteorology

[27] M Rodell and J S Famiglietti ldquoThe potential for satellite-basedmonitoring of groundwater storage changes using GRACE theHigh Plains aquifer Central USrdquo Journal of Hydrology vol 263no 1ndash4 pp 245ndash256 2002

[28] G Strassberg B R Scanlon and M Rodell ldquoComparison ofseasonal terrestrial water storage variations from GRACE withgroundwater-level measurements from the High Plains Aquifer(USA)rdquo Geophysical Research Letters vol 34 no 14 Article IDL14402 2007

[29] M Rodell I Velicogna and J S Famiglietti ldquoSatellite-basedestimates of groundwater depletion in Indiardquo Nature vol 460no 7258 pp 999ndash1002 2009

[30] X Lu and Q Zhuang ldquoEvaluating evapotranspiration andwater-use efficiency of terrestrial ecosystems in the contermi-nous United States using MODIS and AmeriFlux datardquo RemoteSensing of Environment vol 114 no 9 pp 1924ndash1939 2010

[31] M Rodell J S Famiglietti J Chen et al ldquoBasin scale estimatesof evapotranspiration using GRACE and other observationsrdquoGeophysical Research Letters vol 31 no 20 Article ID L205042004

[32] G Ramillien F Frappart AGuntner TNgo-DucA Cazenaveand K Laval ldquoTime variations of the regional evapotranspi-ration rate from Gravity Recovery and Climate Experiment(GRACE) satellite gravimetryrdquo Water Resources Research vol42 no 10 Article ID W10403 2006

[33] S Swenson and J Wahr ldquoEstimating large-scale precipitationminus evapotranspiration from GRACE satellite gravity mea-surementsrdquo Journal of Hydrometeorology vol 7 no 2 pp 252ndash270 2006

[34] M Leblanc P Tregoning G Ramillien S O Tweed andA Fakes ldquoBasin-scale integrated observations of the early21st century multiyear drought in southeast Australiardquo WaterResources Research vol 45 no 4 Article IDW04408 2009

[35] J L Chen C R Wilson B D Tapley Z L Yang and GY Niu ldquo2005 drought event in the Amazon River basin asmeasured byGRACE and estimated by climatemodelsrdquo Journalof Geophysical Research B vol 114 no 5 Article ID B054042009

[36] O B Andersen S I Seneviratne J Hinderer and P ViterboldquoGRACE-derived terrestrial water storage depletion associatedwith the 2003 European heat waverdquo Geophysical ResearchLetters vol 32 no 18 Article ID L18405 pp 1ndash4 2005

[37] F Frappart K Do Minh J LHermitte et al ldquoWater volumechange in the lower Mekong from satellite altimetry andimagery datardquo Geophysical Journal International vol 167 no 2pp 570ndash584 2006

[38] M D Wilson P Bates D Alsdorf et al ldquoModeling large-scale inundation of Amazonian seasonally flooded wetlandsrdquoGeophysical Research Letters vol 34 no 15 Article ID L154042007

[39] S-C Han C K Shum C Jekeli and D Alsdorf ldquoImprovedestimation of terrestrial water storage changes from GRACErdquoGeophysical Research Letters vol 32 no 7 Article ID L07302pp 1ndash5 2005

[40] B Wouters D Chambers and E J O Schrama ldquoGRACEobserves small-scale mass loss in Greenlandrdquo GeophysicalResearch Letters vol 35 no 20 Article ID L20501 2008

[41] I Velicogna and J Wahr ldquoMeasurements of time-variablegravity showmass loss in Antarcticardquo Science vol 311 no 5768pp 1754ndash1756 2006

[42] D C Slobbe P Ditmar and R C Lindenbergh ldquoEstimatingthe rates of mass change ice volume change and snow volume

change in Greenland from ICESat and GRACE datardquo Geophys-ical Journal International vol 176 no 1 pp 95ndash106 2009

[43] P L Svendsen O B Andersen and A A Nielsen ldquoAccelerationof the Greenland ice sheet mass loss as observed by GRACEconfidence and sensitivityrdquo Earth and Planetary Science Lettersvol 364 pp 24ndash29 2013

[44] A S Gardner G Moholdt B Wouters et al ldquoSharply increasedmass loss from glaciers and ice caps in the Canadian ArcticArchipelagordquo Nature vol 473 no 7347 pp 357ndash360 2011

[45] J L Chen B D Tapley and C R Wilson ldquoAlaskan mountainglacial melting observed by satellite gravimetryrdquo Earth andPlanetary Science Letters vol 248 no 1-2 pp 353ndash363 2006

[46] K Matsuo and K Heki ldquoTime-variable ice loss in Asianhigh mountains from satellite gravimetryrdquo Earth and PlanetaryScience Letters vol 290 no 1-2 pp 30ndash36 2010

[47] D Garcıa-Garcıa C C Ummenhofer and V Zlotnicki ldquoAus-tralian water mass variations fromGRACE data linked to Indo-Pacific climate variabilityrdquo Remote Sensing of Environment vol115 no 9 pp 2175ndash2183 2011

[48] W W Immerzeel L P H van Beek and M F P BierkensldquoClimate change will affect the asian water towersrdquo Science vol328 no 5984 pp 1382ndash1385 2010

[49] L S Soslashrensen S B Simonsen K Nielsen et al ldquoMass balanceof the Greenland ice sheet (2003ndash2008) from ICESat datamdashtheimpact of interpolation sampling and firn densityrdquo Cryospherevol 5 no 1 pp 173ndash186 2011

[50] W Zhang Y Wang and C Zhang ldquoThe preliminary analysisof effects of the soil moisture on gravity observationsrdquo Carto-graphica Sinica vol 30 no 2 pp 108ndash111 2001

[51] G Ramillien J S Famiglietti and J Wahr ldquoDetection ofcontinental hydrology and glaciology signals from GRACE areviewrdquo Surveys inGeophysics vol 29 no 4-5 pp 361ndash374 2008

[52] J L Chen C R Wilson R J Eanes and B D TapleyldquoGeophysical contributions to satellite nodal residual variationrdquoJournal of Geophysical Research B vol 104 no 10 pp 23237ndash23244 1999

[53] J K Willis D P Chambers and R S Nerem ldquoAssessing theglobally averaged sea level budget on seasonal to interannualtimescalesrdquo Journal of Geophysical Research C vol 113 no 6Article ID C06015 2008

[54] E W Leuliette and L Miller ldquoClosing the sea level rise budgetwith altimetry Argo and Gracerdquo Geophysical Research Lettersvol 36 no 4 Article ID L04608 2009

[55] J L Chen C RWilson J S Famiglietti andMRodell ldquoAttenu-ation effect on seasonal basin-scale water storage changes fromGRACE time-variable gravityrdquo Journal of Geodesy vol 81 no 4pp 237ndash245 2007

[56] G Zhu J Li HWen and JWang ldquoStudy on variations of globalcontinental water storage with GRACE gravity field modelsrdquoJournal of Geodesy and Geodynamics vol 28 no 5 pp 39ndash442008

[57] S Swenson and J Wahr ldquoMethods for inferring regionalsurface-mass anomalies from Gravity Recovery and ClimateExperiment (GRACE) measurements of time-variable gravityrdquoJournal of Geophysical Research B vol 107 no 9 pp 3-1ndash3-132002

[58] S Swenson and J Wahr ldquoMonitoring changes in continentalwater storage with gracerdquo Space Science Reviews vol 108 no1-2 pp 345ndash354 2003

[59] K-W Seo and C RWilson ldquoSimulated estimation of hydrolog-ical loads fromGRACErdquo Journal of Geodesy vol 78 no 7-8 pp442ndash456 2005

Advances in Meteorology 9

[60] S Swenson and J Wahr ldquoPost-processing removal of correlatederrors in GRACE datardquoGeophysical Research Letters vol 33 no8 Article ID L08402 2006

[61] G Ramillien F Frappart A Cazenave and A Guntner ldquoTimevariations of land water storage from an inversion of 2 years ofGRACE geoidsrdquo Earth and Planetary Science Letters vol 235no 1-2 pp 283ndash301 2005

[62] F Frederic G Ramillien M Leblanc et al ldquoAn independentcomponent analysis filtering approach for estimating continen-tal hydrology in the GRACE gravity datardquo Remote Sensing ofEnvironment vol 115 no 1 pp 187ndash204 2011

[63] S Werth A Guntner R Schmidt and J Kusche ldquoEvaluation ofGRACE filter tools from a hydrological perspectiverdquo Geophysi-cal Journal International vol 179 no 3 pp 1499ndash1515 2009

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Advances in Meteorology 7

(4) TWS changes retrieval based on spatiotemporal vari-ations of gravity field remains considerable uncer-tainty which includes errors produced in the removalof tidal movement and the mass migration becauseof the atmosphere and ocean circulation [11] as wellas the errors in hydrological models used for theestimation of other terrestrial water parameters [6]

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project was supported by National Natural ScienceFoundation of China (Grant no 51309210) and the ChineseAcademy of Sciences (Grant no KZZD-EW-08)

References

[1] Y Huang D Jiang D Zhuang Y Zhu and J Fu ldquoAn improvedapproach for modeling spatial distribution of water use profitmdasha case study in Tuhai Majia Basin Chinardquo Ecological Indicatorsvol 36 pp 94ndash99 2014

[2] Y-H Huang D Jiang D-F Zhuang J-H Wang H-J Yangand H-Y Ren ldquoEvaluation of relative water use efficiency(RWUE) at a regional scale a case study of Tuhai-Majia BasinChinardquo Water Science and Technology vol 66 no 5 pp 927ndash933 2012

[3] J S Famiglietti ldquoRemote sensing of terrestrial water storagesoil moisture and surface watersrdquo in The State of the PlanetFrontiers and Challenges in Geophysics R S J Sparks and C JHawkesworth Eds pp 197ndash207 2004

[4] B D Tapley S Bettadpur M Watkins and C Reigber ldquoThegravity recovery and climate experiment mission overview andearly resultsrdquo Geophysical Research Letters vol 31 no 9 ArticleID L09607 2004

[5] J Wahr S Swenson V Zlotnicki and I Velicogna ldquoTime-variable gravity from GRACE first resultsrdquo GeophysicalResearch Letters vol 31 no 11 Article ID L11501 2004

[6] A Guntner ldquoImprovement of global hydrological models usingGRACE datardquo Surveys in Geophysics vol 29 no 4-5 pp 375ndash397 2008

[7] G Ramillien J S Famiglietti and J Wahr ldquoDetection ofcontinental hydrology and glaciology Signals from GRACE areviewrdquo Surveys inGeophysics vol 29 no 4-5 pp 361ndash374 2008

[8] D P Chambers ldquoConverting 11 Release-04 Gravity Coefficientsinto Maps of Equivalent Water Thicknessrdquo 2007 httpgrace-tellusjplnasagovfilesGRACE-dpc200711 RL04pdf

[9] M Becker W LLovel A Cazenave A Guntner and J-FCretaux ldquoRecent hydrological behavior of the East Africangreat lakes region inferred from GRACE satellite altimetry andrainfall observationsrdquo Comptes Rendus Geoscience vol 342 no3 pp 223ndash233 2010

[10] X Hu J Chen Y Zhou C Huang and X Liao ldquoSeasonal waterstorage change of the Yangtze River basin detected by GracerdquoScience in China D vol 49 no 5 pp 483ndash491 2006

[11] J Wahr M Molenaar and F Bryan ldquoTime variability ofthe Earths gravity field hydrological and oceanic effects and

their possible detection using GRACErdquo Journal of GeophysicalResearch B vol 103 no 12 pp 30205ndash30229 1998

[12] M Rodell and J S Famiglietti ldquoDetectability of variations incontinental water storage from satellite observations of the timedependent gravity fieldrdquo Water Resources Research vol 35 no9 pp 2705ndash2723 1999

[13] M Rodell and J S Famiglietti ldquoAn analysis of terrestrial waterstorage variations in Illinois with implications for the GravityRecovery and Climate Experiment (GRACE)rdquoWater ResourcesResearch vol 37 no 5 pp 1327ndash1339 2001

[14] M Zhong J Duan H Xu P Peng H Yan and Y ZhuldquoTrend of China land water storage redistribution at medi-and large-spatial scales in recent five years by satellite gravityobservationsrdquo Chinese Science Bulletin vol 54 no 5 pp 816ndash821 2009

[15] H Wang L Jia H Steffen et al ldquoIncreased water storage inNorth America and Scandinavia from GRACE gravity datardquoNature Geoscience vol 6 no 1 pp 38ndash42 2013

[16] S C Swenson and P C D Milly ldquoClimate model biases inseasonally of continental water storage revealed by satellitegravimetryrdquoWater Resources Research vol 42 no 3 Article IDW03201 2006

[17] T H Syed J S FamigliettiM Rodell J Chen andC RWilsonldquoAnalysis of terrestrial water storage changes from GRACE andGLDASrdquo Water Resources Research vol 44 no 2 Article IDW02433 2008

[18] G-Y Niu and Z-L Yang ldquoAssessing a land surface modelsimprovements with GRACE estimatesrdquo Geophysical ResearchLetters vol 33 no 7 Article ID L07401 2006

[19] T Ngo-Duc K Laval G Ramillien J Polcher and A CazenaveldquoValidation of the land water storage simulated by OrganisingCarbon and Hydrology in Dynamic Ecosystems (ORCHIDEE)with Gravity Recovery and Climate Experiment (GRACE)datardquo Water Resources Research vol 43 no 4 Article IDW04427 2007

[20] J L Chen C R Wilson B D Tapley and J C Ries ldquoLowdegree gravitational changes from GRACE validation andinterpretationrdquo Geophysical Research Letters vol 31 no 22Article ID L22607 pp 1ndash5 2004

[21] R Klees E A Revtova B C Gunter et al ldquoThe design of anoptimal filter for monthly GRACE gravity modelsrdquo GeophysicalJournal International vol 175 no 2 pp 417ndash432 2008

[22] K-W Seo C R Wilson J S Famiglietti J L Chen andM Rodell ldquoTerrestrial water mass load changes from GravityRecovery and Climate Experiment (GRACE)rdquoWater ResourcesResearch vol 42 no 5 Article ID W05417 2006

[23] B D Tapley S Bettadpur J C Ries P F Thompson and MM Watkins ldquoGRACE measurements of mass variability in theEarth systemrdquo Science vol 305 no 5683 pp 503ndash505 2004

[24] D P Lettenmaier and J S Famiglietti ldquoHydrology water fromon highrdquo Nature vol 444 no 7119 pp 562ndash563 2006

[25] S Swenson P J-F Yeh J Wahr and J Famiglietti ldquoA compari-son of terrestrial water storage variations from GRACE with insitu measurements from Illinoisrdquo Geophysical Research Lettersvol 33 no 16 Article ID L16401 2006

[26] L Xavier M Becker A Cazenave L Longuevergne W Lloveland O C R Filho ldquoInterannual variability in water storageover 2003ndash2008 in the Amazon Basin from GRACE spacegravimetry in situ river level and precipitation datardquo RemoteSensing of Environment vol 114 no 8 pp 1629ndash1637 2010

8 Advances in Meteorology

[27] M Rodell and J S Famiglietti ldquoThe potential for satellite-basedmonitoring of groundwater storage changes using GRACE theHigh Plains aquifer Central USrdquo Journal of Hydrology vol 263no 1ndash4 pp 245ndash256 2002

[28] G Strassberg B R Scanlon and M Rodell ldquoComparison ofseasonal terrestrial water storage variations from GRACE withgroundwater-level measurements from the High Plains Aquifer(USA)rdquo Geophysical Research Letters vol 34 no 14 Article IDL14402 2007

[29] M Rodell I Velicogna and J S Famiglietti ldquoSatellite-basedestimates of groundwater depletion in Indiardquo Nature vol 460no 7258 pp 999ndash1002 2009

[30] X Lu and Q Zhuang ldquoEvaluating evapotranspiration andwater-use efficiency of terrestrial ecosystems in the contermi-nous United States using MODIS and AmeriFlux datardquo RemoteSensing of Environment vol 114 no 9 pp 1924ndash1939 2010

[31] M Rodell J S Famiglietti J Chen et al ldquoBasin scale estimatesof evapotranspiration using GRACE and other observationsrdquoGeophysical Research Letters vol 31 no 20 Article ID L205042004

[32] G Ramillien F Frappart AGuntner TNgo-DucA Cazenaveand K Laval ldquoTime variations of the regional evapotranspi-ration rate from Gravity Recovery and Climate Experiment(GRACE) satellite gravimetryrdquo Water Resources Research vol42 no 10 Article ID W10403 2006

[33] S Swenson and J Wahr ldquoEstimating large-scale precipitationminus evapotranspiration from GRACE satellite gravity mea-surementsrdquo Journal of Hydrometeorology vol 7 no 2 pp 252ndash270 2006

[34] M Leblanc P Tregoning G Ramillien S O Tweed andA Fakes ldquoBasin-scale integrated observations of the early21st century multiyear drought in southeast Australiardquo WaterResources Research vol 45 no 4 Article IDW04408 2009

[35] J L Chen C R Wilson B D Tapley Z L Yang and GY Niu ldquo2005 drought event in the Amazon River basin asmeasured byGRACE and estimated by climatemodelsrdquo Journalof Geophysical Research B vol 114 no 5 Article ID B054042009

[36] O B Andersen S I Seneviratne J Hinderer and P ViterboldquoGRACE-derived terrestrial water storage depletion associatedwith the 2003 European heat waverdquo Geophysical ResearchLetters vol 32 no 18 Article ID L18405 pp 1ndash4 2005

[37] F Frappart K Do Minh J LHermitte et al ldquoWater volumechange in the lower Mekong from satellite altimetry andimagery datardquo Geophysical Journal International vol 167 no 2pp 570ndash584 2006

[38] M D Wilson P Bates D Alsdorf et al ldquoModeling large-scale inundation of Amazonian seasonally flooded wetlandsrdquoGeophysical Research Letters vol 34 no 15 Article ID L154042007

[39] S-C Han C K Shum C Jekeli and D Alsdorf ldquoImprovedestimation of terrestrial water storage changes from GRACErdquoGeophysical Research Letters vol 32 no 7 Article ID L07302pp 1ndash5 2005

[40] B Wouters D Chambers and E J O Schrama ldquoGRACEobserves small-scale mass loss in Greenlandrdquo GeophysicalResearch Letters vol 35 no 20 Article ID L20501 2008

[41] I Velicogna and J Wahr ldquoMeasurements of time-variablegravity showmass loss in Antarcticardquo Science vol 311 no 5768pp 1754ndash1756 2006

[42] D C Slobbe P Ditmar and R C Lindenbergh ldquoEstimatingthe rates of mass change ice volume change and snow volume

change in Greenland from ICESat and GRACE datardquo Geophys-ical Journal International vol 176 no 1 pp 95ndash106 2009

[43] P L Svendsen O B Andersen and A A Nielsen ldquoAccelerationof the Greenland ice sheet mass loss as observed by GRACEconfidence and sensitivityrdquo Earth and Planetary Science Lettersvol 364 pp 24ndash29 2013

[44] A S Gardner G Moholdt B Wouters et al ldquoSharply increasedmass loss from glaciers and ice caps in the Canadian ArcticArchipelagordquo Nature vol 473 no 7347 pp 357ndash360 2011

[45] J L Chen B D Tapley and C R Wilson ldquoAlaskan mountainglacial melting observed by satellite gravimetryrdquo Earth andPlanetary Science Letters vol 248 no 1-2 pp 353ndash363 2006

[46] K Matsuo and K Heki ldquoTime-variable ice loss in Asianhigh mountains from satellite gravimetryrdquo Earth and PlanetaryScience Letters vol 290 no 1-2 pp 30ndash36 2010

[47] D Garcıa-Garcıa C C Ummenhofer and V Zlotnicki ldquoAus-tralian water mass variations fromGRACE data linked to Indo-Pacific climate variabilityrdquo Remote Sensing of Environment vol115 no 9 pp 2175ndash2183 2011

[48] W W Immerzeel L P H van Beek and M F P BierkensldquoClimate change will affect the asian water towersrdquo Science vol328 no 5984 pp 1382ndash1385 2010

[49] L S Soslashrensen S B Simonsen K Nielsen et al ldquoMass balanceof the Greenland ice sheet (2003ndash2008) from ICESat datamdashtheimpact of interpolation sampling and firn densityrdquo Cryospherevol 5 no 1 pp 173ndash186 2011

[50] W Zhang Y Wang and C Zhang ldquoThe preliminary analysisof effects of the soil moisture on gravity observationsrdquo Carto-graphica Sinica vol 30 no 2 pp 108ndash111 2001

[51] G Ramillien J S Famiglietti and J Wahr ldquoDetection ofcontinental hydrology and glaciology signals from GRACE areviewrdquo Surveys inGeophysics vol 29 no 4-5 pp 361ndash374 2008

[52] J L Chen C R Wilson R J Eanes and B D TapleyldquoGeophysical contributions to satellite nodal residual variationrdquoJournal of Geophysical Research B vol 104 no 10 pp 23237ndash23244 1999

[53] J K Willis D P Chambers and R S Nerem ldquoAssessing theglobally averaged sea level budget on seasonal to interannualtimescalesrdquo Journal of Geophysical Research C vol 113 no 6Article ID C06015 2008

[54] E W Leuliette and L Miller ldquoClosing the sea level rise budgetwith altimetry Argo and Gracerdquo Geophysical Research Lettersvol 36 no 4 Article ID L04608 2009

[55] J L Chen C RWilson J S Famiglietti andMRodell ldquoAttenu-ation effect on seasonal basin-scale water storage changes fromGRACE time-variable gravityrdquo Journal of Geodesy vol 81 no 4pp 237ndash245 2007

[56] G Zhu J Li HWen and JWang ldquoStudy on variations of globalcontinental water storage with GRACE gravity field modelsrdquoJournal of Geodesy and Geodynamics vol 28 no 5 pp 39ndash442008

[57] S Swenson and J Wahr ldquoMethods for inferring regionalsurface-mass anomalies from Gravity Recovery and ClimateExperiment (GRACE) measurements of time-variable gravityrdquoJournal of Geophysical Research B vol 107 no 9 pp 3-1ndash3-132002

[58] S Swenson and J Wahr ldquoMonitoring changes in continentalwater storage with gracerdquo Space Science Reviews vol 108 no1-2 pp 345ndash354 2003

[59] K-W Seo and C RWilson ldquoSimulated estimation of hydrolog-ical loads fromGRACErdquo Journal of Geodesy vol 78 no 7-8 pp442ndash456 2005

Advances in Meteorology 9

[60] S Swenson and J Wahr ldquoPost-processing removal of correlatederrors in GRACE datardquoGeophysical Research Letters vol 33 no8 Article ID L08402 2006

[61] G Ramillien F Frappart A Cazenave and A Guntner ldquoTimevariations of land water storage from an inversion of 2 years ofGRACE geoidsrdquo Earth and Planetary Science Letters vol 235no 1-2 pp 283ndash301 2005

[62] F Frederic G Ramillien M Leblanc et al ldquoAn independentcomponent analysis filtering approach for estimating continen-tal hydrology in the GRACE gravity datardquo Remote Sensing ofEnvironment vol 115 no 1 pp 187ndash204 2011

[63] S Werth A Guntner R Schmidt and J Kusche ldquoEvaluation ofGRACE filter tools from a hydrological perspectiverdquo Geophysi-cal Journal International vol 179 no 3 pp 1499ndash1515 2009

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

8 Advances in Meteorology

[27] M Rodell and J S Famiglietti ldquoThe potential for satellite-basedmonitoring of groundwater storage changes using GRACE theHigh Plains aquifer Central USrdquo Journal of Hydrology vol 263no 1ndash4 pp 245ndash256 2002

[28] G Strassberg B R Scanlon and M Rodell ldquoComparison ofseasonal terrestrial water storage variations from GRACE withgroundwater-level measurements from the High Plains Aquifer(USA)rdquo Geophysical Research Letters vol 34 no 14 Article IDL14402 2007

[29] M Rodell I Velicogna and J S Famiglietti ldquoSatellite-basedestimates of groundwater depletion in Indiardquo Nature vol 460no 7258 pp 999ndash1002 2009

[30] X Lu and Q Zhuang ldquoEvaluating evapotranspiration andwater-use efficiency of terrestrial ecosystems in the contermi-nous United States using MODIS and AmeriFlux datardquo RemoteSensing of Environment vol 114 no 9 pp 1924ndash1939 2010

[31] M Rodell J S Famiglietti J Chen et al ldquoBasin scale estimatesof evapotranspiration using GRACE and other observationsrdquoGeophysical Research Letters vol 31 no 20 Article ID L205042004

[32] G Ramillien F Frappart AGuntner TNgo-DucA Cazenaveand K Laval ldquoTime variations of the regional evapotranspi-ration rate from Gravity Recovery and Climate Experiment(GRACE) satellite gravimetryrdquo Water Resources Research vol42 no 10 Article ID W10403 2006

[33] S Swenson and J Wahr ldquoEstimating large-scale precipitationminus evapotranspiration from GRACE satellite gravity mea-surementsrdquo Journal of Hydrometeorology vol 7 no 2 pp 252ndash270 2006

[34] M Leblanc P Tregoning G Ramillien S O Tweed andA Fakes ldquoBasin-scale integrated observations of the early21st century multiyear drought in southeast Australiardquo WaterResources Research vol 45 no 4 Article IDW04408 2009

[35] J L Chen C R Wilson B D Tapley Z L Yang and GY Niu ldquo2005 drought event in the Amazon River basin asmeasured byGRACE and estimated by climatemodelsrdquo Journalof Geophysical Research B vol 114 no 5 Article ID B054042009

[36] O B Andersen S I Seneviratne J Hinderer and P ViterboldquoGRACE-derived terrestrial water storage depletion associatedwith the 2003 European heat waverdquo Geophysical ResearchLetters vol 32 no 18 Article ID L18405 pp 1ndash4 2005

[37] F Frappart K Do Minh J LHermitte et al ldquoWater volumechange in the lower Mekong from satellite altimetry andimagery datardquo Geophysical Journal International vol 167 no 2pp 570ndash584 2006

[38] M D Wilson P Bates D Alsdorf et al ldquoModeling large-scale inundation of Amazonian seasonally flooded wetlandsrdquoGeophysical Research Letters vol 34 no 15 Article ID L154042007

[39] S-C Han C K Shum C Jekeli and D Alsdorf ldquoImprovedestimation of terrestrial water storage changes from GRACErdquoGeophysical Research Letters vol 32 no 7 Article ID L07302pp 1ndash5 2005

[40] B Wouters D Chambers and E J O Schrama ldquoGRACEobserves small-scale mass loss in Greenlandrdquo GeophysicalResearch Letters vol 35 no 20 Article ID L20501 2008

[41] I Velicogna and J Wahr ldquoMeasurements of time-variablegravity showmass loss in Antarcticardquo Science vol 311 no 5768pp 1754ndash1756 2006

[42] D C Slobbe P Ditmar and R C Lindenbergh ldquoEstimatingthe rates of mass change ice volume change and snow volume

change in Greenland from ICESat and GRACE datardquo Geophys-ical Journal International vol 176 no 1 pp 95ndash106 2009

[43] P L Svendsen O B Andersen and A A Nielsen ldquoAccelerationof the Greenland ice sheet mass loss as observed by GRACEconfidence and sensitivityrdquo Earth and Planetary Science Lettersvol 364 pp 24ndash29 2013

[44] A S Gardner G Moholdt B Wouters et al ldquoSharply increasedmass loss from glaciers and ice caps in the Canadian ArcticArchipelagordquo Nature vol 473 no 7347 pp 357ndash360 2011

[45] J L Chen B D Tapley and C R Wilson ldquoAlaskan mountainglacial melting observed by satellite gravimetryrdquo Earth andPlanetary Science Letters vol 248 no 1-2 pp 353ndash363 2006

[46] K Matsuo and K Heki ldquoTime-variable ice loss in Asianhigh mountains from satellite gravimetryrdquo Earth and PlanetaryScience Letters vol 290 no 1-2 pp 30ndash36 2010

[47] D Garcıa-Garcıa C C Ummenhofer and V Zlotnicki ldquoAus-tralian water mass variations fromGRACE data linked to Indo-Pacific climate variabilityrdquo Remote Sensing of Environment vol115 no 9 pp 2175ndash2183 2011

[48] W W Immerzeel L P H van Beek and M F P BierkensldquoClimate change will affect the asian water towersrdquo Science vol328 no 5984 pp 1382ndash1385 2010

[49] L S Soslashrensen S B Simonsen K Nielsen et al ldquoMass balanceof the Greenland ice sheet (2003ndash2008) from ICESat datamdashtheimpact of interpolation sampling and firn densityrdquo Cryospherevol 5 no 1 pp 173ndash186 2011

[50] W Zhang Y Wang and C Zhang ldquoThe preliminary analysisof effects of the soil moisture on gravity observationsrdquo Carto-graphica Sinica vol 30 no 2 pp 108ndash111 2001

[51] G Ramillien J S Famiglietti and J Wahr ldquoDetection ofcontinental hydrology and glaciology signals from GRACE areviewrdquo Surveys inGeophysics vol 29 no 4-5 pp 361ndash374 2008

[52] J L Chen C R Wilson R J Eanes and B D TapleyldquoGeophysical contributions to satellite nodal residual variationrdquoJournal of Geophysical Research B vol 104 no 10 pp 23237ndash23244 1999

[53] J K Willis D P Chambers and R S Nerem ldquoAssessing theglobally averaged sea level budget on seasonal to interannualtimescalesrdquo Journal of Geophysical Research C vol 113 no 6Article ID C06015 2008

[54] E W Leuliette and L Miller ldquoClosing the sea level rise budgetwith altimetry Argo and Gracerdquo Geophysical Research Lettersvol 36 no 4 Article ID L04608 2009

[55] J L Chen C RWilson J S Famiglietti andMRodell ldquoAttenu-ation effect on seasonal basin-scale water storage changes fromGRACE time-variable gravityrdquo Journal of Geodesy vol 81 no 4pp 237ndash245 2007

[56] G Zhu J Li HWen and JWang ldquoStudy on variations of globalcontinental water storage with GRACE gravity field modelsrdquoJournal of Geodesy and Geodynamics vol 28 no 5 pp 39ndash442008

[57] S Swenson and J Wahr ldquoMethods for inferring regionalsurface-mass anomalies from Gravity Recovery and ClimateExperiment (GRACE) measurements of time-variable gravityrdquoJournal of Geophysical Research B vol 107 no 9 pp 3-1ndash3-132002

[58] S Swenson and J Wahr ldquoMonitoring changes in continentalwater storage with gracerdquo Space Science Reviews vol 108 no1-2 pp 345ndash354 2003

[59] K-W Seo and C RWilson ldquoSimulated estimation of hydrolog-ical loads fromGRACErdquo Journal of Geodesy vol 78 no 7-8 pp442ndash456 2005

Advances in Meteorology 9

[60] S Swenson and J Wahr ldquoPost-processing removal of correlatederrors in GRACE datardquoGeophysical Research Letters vol 33 no8 Article ID L08402 2006

[61] G Ramillien F Frappart A Cazenave and A Guntner ldquoTimevariations of land water storage from an inversion of 2 years ofGRACE geoidsrdquo Earth and Planetary Science Letters vol 235no 1-2 pp 283ndash301 2005

[62] F Frederic G Ramillien M Leblanc et al ldquoAn independentcomponent analysis filtering approach for estimating continen-tal hydrology in the GRACE gravity datardquo Remote Sensing ofEnvironment vol 115 no 1 pp 187ndash204 2011

[63] S Werth A Guntner R Schmidt and J Kusche ldquoEvaluation ofGRACE filter tools from a hydrological perspectiverdquo Geophysi-cal Journal International vol 179 no 3 pp 1499ndash1515 2009

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Advances in Meteorology 9

[60] S Swenson and J Wahr ldquoPost-processing removal of correlatederrors in GRACE datardquoGeophysical Research Letters vol 33 no8 Article ID L08402 2006

[61] G Ramillien F Frappart A Cazenave and A Guntner ldquoTimevariations of land water storage from an inversion of 2 years ofGRACE geoidsrdquo Earth and Planetary Science Letters vol 235no 1-2 pp 283ndash301 2005

[62] F Frederic G Ramillien M Leblanc et al ldquoAn independentcomponent analysis filtering approach for estimating continen-tal hydrology in the GRACE gravity datardquo Remote Sensing ofEnvironment vol 115 no 1 pp 187ndash204 2011

[63] S Werth A Guntner R Schmidt and J Kusche ldquoEvaluation ofGRACE filter tools from a hydrological perspectiverdquo Geophysi-cal Journal International vol 179 no 3 pp 1499ndash1515 2009

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in