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The EDDI User Guidev1.0 – September 2017
Jeff Lukas, Mike Hobbins, Imtiaz Rangwala and the EDDI team
Contents- UseBookmarks inPDFtonavigate1) Cover2) Contents3) Theintendedaudience4) WhatthisUserGuideprovides5) EDDIinanutshell6) KeyfeaturesofEDDI7) WhatEDDIisnot8) Drought=moisture imbalance9) AboutEvaporativeDemand(E0)10) NormalE0 variesacrosstheUS11) Largeseasonalcycle inE012) TherelationshipbetweenETandE013) HighE0=surfacemoisturestress14) IncreasingE0reflectsdroughtintensification15) HowEDDIiscalculated16) EDDIcategories17) Seasonalinterpretation ofEDDI18) EDDIcomparedwithotherindicators19) EDDIcomparedwithotherindicators20) Comparingdifferentindicators21) Convergenceofevidence fordrought22) BasicsofreadinganEDDImap23) InterpretingEDDIatdifferenttimescales24) InterpretingEDDIatdifferenttimescales25) EDDIgivesearlywarningofflashdrought
26) Moreflashdroughtearly-warning27) NotallEDDIhotspotsbecomedrought28) EDDIinagricultural droughtmonitoring29) Potentialapplicationsinfire&hydrology30) DecomposingE0toseedroughtdrivers31) Wheretogetcurrent EDDImaps32) Wheretogetpast EDDImaps33) WheretogetEDDItime-series34) Technical backgroundonEDDI35) Acknowledgements
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ThisUserGuideisintendedfor:• Managers: Thosewhomonitordrought
conditions inordertomanageresourcesandmakedecisions;e.g.,agproducers,andwater,fire,forests,range,andwildlifemanagers
• Translators:Thosewhoworkcloselywiththeabovegroups inanadvisoryoroutreachroleand/ordisseminatedrought information;e.g.,NWSforecasters,Stateclimatologists,droughtcoordinators
• Researchers: Thosewhostudythedroughtphenomenon tobetterunderstand itscauses,manifestations,andimpacts
• Thelevelofinformation intheGuideismostsuitedforthefirsttwogroups.Butresearchersmayfind theoverviewusefulbeforedelvingmoreintothetechnicalbackground onEDDI. 3
WhatthisUserGuideprovidesClearandconciseexplanationsof:
• EvaporativeDemand (E0)andwhyitisimportanttodrought
• HowEDDIiscalculatedandhowitdepictsEvaporativeDemand
• HowEDDIrelatestootherdrought indicators
• HowtointerpretEDDImapsoverdifferent timewindows
ThisUserGuidewillbeupdatedbasedonuserfeedback.Pleaseletusknowifitwashelpful,andhowitmightbeimproved.
SendfeedbacktoJeffLukas,lukas@colorado.edu4
EDDIinanutshell
• EDDIisadrought indexbasedonthe“thirst”oftheatmosphere—whichleadstothedrying ofsoilsandvegetation,andalsoreflectsthatdrying
• Moretechnically:EDDIshowstheanomaly*indailyevaporativedemandaggregatedoveraspecified timewindow,atagivenlocation
• EDDIiscalculatedfromobservationsoftheatmospherenearthelandsurface:temperature,humidity, windspeed,andsolarradiation
• EDDIcanprovideaddedvaluetootherdrought indicators,especiallyforearlywarningandflashdroughtdetection
*i.e.,theunusualness ofthecurrentconditionsascomparedtotherangeofhistorical conditions 5
KeyfeaturesofEDDI
• EDDImapsareproduced innear-real-time,witha~5-daylag
• EDDIiscalculatedovermultiple timewindows(like theStandardizedPrecipitationIndex;SPI),tosuitdifferentapplications
• EDDImapshaveaspatialresolutionof1/8-degree(~12kmor~7miles)
• EDDIusesaclassificationschemethatisequivalenttotheUSDroughtMonitorcategories(D0,D1,D2,etc.)
• EDDIisnotsensitivetotheland-covertype,soitisappropriate foruseinallregions
6
WhatEDDIisnot
• EDDIdoesn’tdirectlymeasureon-the-ground conditions—thoughEDDIvaluesarestronglyinfluencedbysurfacemoistureconditions
• EDDIisnotadroughtprediction,butatshorttimescales,itindicatesthepotential fordroughtemergence
• EDDIisnotameasureofactualevapotranspiration (i.e.,ET)
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Droughtresultsfrommoistureimbalanceatthelandsurface
RUNOFF
PRECIPITATION
ETE0
• Themoisturestatusatthelandsurfacereflectsthebalanceofgainsfromprecipitation andlossesfromevapotranspiration (ET)
• Drought (inadequatesurfacemoisture) istypicallyinitiatedbybelow-normalprecipitation(reducedgains),andworsened byabove-normalevaporativedemand (increasedlosses)
• ETistherateofactualmoisturelosstotheatmosphere,usuallyexpressedasin./dayormm/day,fromsoils,openwater,and/orvegetationatonelocation
• ETiscoupled toevaporativedemand(E0) butunlikeE0,ET isconstrainedbythesurfacemoisturesupply
• ETcanneverexceedE0,andisoftenless 8
Evaporativedemand(E0)isthe“thirstoftheatmosphere”
fao.org
• E0 istheETthatwouldoccurgivenanunlimitedsurfacemoisturesupply
• E0 iseasiertoquantify thanET
• E0 canestimatedbyoneofseveralmethods:
o ReferenceET(ET0)o PotentialET(PET)o Panevaporation
• AccurateestimatesofReferenceET,suchasusedinEDDI,requirethesevariables:
o Temperatureo Humidityo Windspeedo Solarradiation
9
MeanannualE0 (mm),1981-2010
The“normal”E0 varieswidelyfromplacetoplace,withhigherE0indryandhotplaceslikewestTexas,andlowerE0incoolandwetplaceslikeMaine
The mean annual E0 varies by a factor of ~3 between the dry-hot Southwest and the cool-wet Northeast
Figure: Mike Hobbins, adapted from Hobbins (2016), Trans. ABABE
10
E0hasalargeseasonalcycle,peakinginthesummer
Daily E0 for the Midwest US (1980-2016), with summer values highlighted
• WhenE0 inthesummer isevenhigher thanusual(asin2012,below) itoftenreflectstheonsetorrapidintensificationofdroughtconditions
11
Time
Surface moisture availability
Evapotranspiration(ET)
Evaporative Demand(E0)
Moisture is notlimitingET ~ E0
Moisture is limiting E0 > ET
Feedback from the drying land surface increases E0
TherelationshipbetweenE0 andET changesasthelandsurfacedriesout
• Whensufficient surfacemoistureisavailable,risingE0 leadstorisingET
• Whenmoisture islimited,ET declines,whileE0 risesevenmoresteeply
• Regionswithamorearidclimate(yellowandredbelow)areoften inthemoisture-limitedstateunder ‘normal’ conditions
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Inotherwords:Unusuallyhighevaporativedemand(E0)canleadtomoisturestressonthelandsurface,andultimatelytodrought—evenwhenprecipitationhasbeennear-normal
E0
ET
Soil Moisture
13
Oncedroughthasdeveloped,thenow-drylandsurfacemakestheairabovethesurfacewarmeranddrier—whichfurtherincreasesevaporative demand
E0
ET
Soil Moisture
14
HowEDDIiscalculated
Startwithmeteorologicalinputs foreachgridcell(temperature,humidity,windspeed, solarradiation)
fromNLDAS-2,1/8-degreegriddedmetdata
CalculatedailyReferenceET(ET0;estimateofE0)andaggregateitovertheselectedtimewindowusingtheASCEvariantofthePenman-Monteith equation*
DeterminewherethataggregatedE0 valueslotsintotheclimatology(1980-present) foreachgridcell
usingrank-basednon-parametricprobabilities
Higher E0than normal
Lower E0 than normal
Temperature
Humidity Wind speed
Radiation
Temperature Humidity
Wind speed
Radiation
*identicaltotheFA056variantofthePenman-Monteith atdailytimescales
EDDI15
100th2 5 10 20 30 70 80 90 95 98Percentile
ED0 ED1 ED2 34 ED0ED1ED23 4EDDI Category 4
Onthedryend,EDDIusesthesamepercentilebreaksasintheUSDroughtMonitor
Higher E0than normal
Lower E0 than normal
EDDIcategoriesarederivedfromthedistributionofaggregatedE0values;selectedpercentilesusedasthresholdsforthecategories
ObserveddistributionofE0from1980-present forthegivenlocationandtimewindow
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Inthesummer,anygivenEDDIcategorywillreflectamuchlargeraggregatedE0 valuethaninotherseasons
• SowhenEDDIisinadrought categoryduring thesummer, thedroughtimpactsaregenerallygreaterthanduring thecoolerseasons
• Thatsaid,emergenceofED3orED4inotherseasonscanstillindicatehigh riskof significantimpacts,suchaswildfires (below,Sunshine Fire)
Daily E0 for Boulder, CO, with 30-day running mean (2009-2017)
2010 2011 2012 2013 2014 2015 2016 2017
June 25, 2012 – Flagstaff Fire 1-month EDDI: ED4
March 19, 2017 – Sunshine Fire 1-month EDDI: ED4
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HowthephysicalbasisofEDDIcompareswithotherdroughtindicators- partI
E0
EDDIAnomalyinestimatedEvaporativeDemand(E0)overauser-selectedtimewindow,whereE0isestimatedfromobservedTemperature,Humidity,Windspeed,andsolarRadiation
SPI(StandardizedPrecipitationIndex)AnomalyinobservedPrecipitation(P)overauser-selectedtimewindow ofinterestP
SPEI(StandardizedPrecipitation-EvapotranspirationIndex)Anomalyinthedifferencebetween observed Precipitation(P)andestimatedPotentialEvapotranspiration(PET;equivalentto E0*)overauser-selectedtimewindow
P
PDSI(PalmerDroughtSeverityIndex)Simulatedsoil-moisturebalanceanomaly,calculatedfromobservedPrecipitation(P)andanestimateofE0*,withaneffectivetimewindow of~6-12months
P
*SomesourcesofSPEIandPDSImapsanddatauseafullyphysicalestimateofE0;othersusearoughestimateofE0fromTemperatureonly
E0
E0
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E0
EDDIAnomalyinestimatedEvaporativeDemand(E0)overauser-selectedtimewindow,whereE0isestimatedfromobservedTemperature,Humidity,Windspeed,andsolarRadiation
ESI(EvaporativeStressIndex)AnomalyintheratioofETtoE0,whereETiscalculatedusingleaf-areaindex(LAI)andland-surfaceTemperaturefromsatellitedata,andE0isfromafullyphysicalestimate,overauser-selectedtimewindow
USDM (U.S.DroughtMonitor)Quasi-objectiveblendofmultipledroughtindicators:SPI,PalmerIndices,modeledsoilmoisture,observedstreamflow,reporteddrought impacts,andother indicators;inherenttimewindow variesbyseason/region
P
P
ET
VegDRIBlendofmultipledroughtindicators:9-monthSPI,PalmerIndex,andsatellite-sensedvegetationgreennessandleaf-outanomaly;effectivetimewindowofseveralmonthsvegetation
HowthephysicalbasisofEDDIcompareswithotherdroughtindicators- partII
T (~E0)
E0
T (~E0)
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It'sgoodpracticetocomparedifferentdroughtindicators
E0(T)
PE0(T)
P
E0(T)ET
vegetation
E0
E0(T)
P
PE0(T)
P
• EDDIandtheotherindicatorscapturedifferentaspectsofthemoisturebalanceatthelandsurface;EDDIisunique infocusingonevaporativedemand
• Differentindicatorsalsohavedifferent timewindowsoverwhichconditionsareaggregated—whether thewindowisuser-selectedor“bakedinto”thatindex
• Thus,different indicatorscanspeaktosomedroughtimpactsbetterthanothers
• Lookingatmultipleindicatorsprovidesa“convergenceofevidence”,e.g.,tosupportadrought designation
• Thedifferencesbetweenindicatorscanalsoprovideinsight intohowdroughtconditionsareemergingandcausingimpacts
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Forexample,the3-monthEDDIforMay-July2002showsadroughtpatternverysimilartootherindicatorsusedforagricultural droughtimpacts(“convergenceofevidence”)
July 31, 2002
USDM 3-month EDDI
VIC-modeled Soil Moisture 3-month Evaporative Stress Index (ESI)
21
ThebasicsofreadinganEDDImapAn“EDDImonth”is30days,sothis3-monthmapisbasedonevaporativedemandfromFebruary4toMay4,2017(90days).
ThemostrecentEDDImapslagthecurrentdateby~5days—sothismapwasreleasedaroundMay9,2017
Evaporativedemandwasunusuallyhigh forFeb4-May4intheOhioValley,Florida,andthewesternGreatPlains.(ED4meansthatconditionsthisdryareexpected inonly2%ofFeb4-May4periods.)
Evaporativedemandwasunusuallylow forFeb4-May4inthePacificNorthwestintotheRockies.
Thenames,colors,andpercentile breaksforthedroughtcategoriesareanalogoustothosefortheUSDroughtMonitor.
TheDroughtandWetnesscategoriesforagivennumberhavethesameexpected frequency(e.g.,ED2andEW2). 22
2-weekEDDI12-monthEDDI
InterpretingEDDIatdifferenttimescalesThesimpleversion:Long-term(>3-month)= droughthasemergedorispersistingShort-term (2-weekto3-month)=potential fordrought emergence/intensification
Unusuallyhighevaporativedemandoverpast12monthsinsouthernNewEnglandandOhioValleyreflectspersistentlydrysurfaceconditions(i.e.,drought)
Above-normalevaporativedemandover2weeksinSouthwest andSouthern Plainscouldsignaldroughtemergence 23
InterpretingEDDIatdifferenttimescalesBycomparingdifferenttimewindows,youcaninferchangesandtrends
2-week(Apr21– May4)
3-month(Feb5– May4)
12-month(May5- May4)
6-month(Nov5– May4)
Eastern ColoradoMost recent 2 weeks have had below-normal evaporative demand (EW1), a change from prior above-normal demand
Overall, early spring had unusually high evaporative demand (ED3 and ED4), strongly indicating drought emergence
Winter and early spring had high evaporative demand overall (ED1-ED4), with higher values for early spring than for winter
The past 12 months saw high evaporative demand overall (mainly ED1), led by the very high values in winter and early spring
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EDDIcangiveearlywarningofflashdrought—i.e.,rapid-onsetdroughtthatdevelopsinseveralweeks
• InMay-July2012,the2-weekEDDIcapturedseveredroughtconditions intheMidwestup to~2monthsbeforetheUSDroughtMonitor
USDroughtMonitor 2-weekEDDI
25
Moreflash-droughtearlywarning:InMay-July2017intheNorthernPlains,the1-monthEDDIpickedupthedroughtsignalineasternMontana1-4weeksaheadofthe1-monthESI
Figures: Dan McEvoy (EDDI); Chris Hain (ESI)
1-month EDDI 1-monthESI
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June 4, 2017Evaporative demand normal or low across
region
Keepinmind:NotallareaswithnewEDDI“hotspots”atshorttimewindows(e.g.,2weeks,1month)willseepersistenceofdryconditionsandemergenceofdroughtimpacts,butmanywill—sotheyareworthkeepinganeyeon,especiallyinspringandsummer
1-month EDDI in Four Corners region (UT, CO, AZ, NM)
July 4, 2017Unusually high
evaporative demand in June – which is typically a dry month anyways –
WATCH OUT
August 4, 2017OK - July monsoon rains came in well
above normal; unusually low
evaporative demand 27
Agriculturaldroughtmonitoringwiththe2-weekEDDISummer2015intheWindRiverIndianReservation,north-centralWyoming:EDDIshowsanomalouslyhighE0 fromearlyAugust;agimpactsoccurred
throughout September;USDMfinallyshowssomedrying inlateSeptember
Figure:CandidaDewes,NOAAPSD
IMPACTS IMPACTS IMPACTS
28
Ongoingresearch:PotentialapplicationsofEDDIinwildfireriskmonitoringandhydrologicmonitoringarebeingevaluated
12-m
onth
E0
inJu
ne (m
m)
1000-hour fuel moisture, May-Oct (%)
R 2 = 0.74
E0- fuelmoisturerelationshipacrossS.California• E0 /EDDIshowstrongrelationshipswith
seasonalfuelmoisture(right) andseasonalrunoff (below), despitenotincluding precipitationdirectly
• Researchisongoing toassesstheaddedvalueofEDDIrelativetomoretraditionalindicatorsinthesefields
R 2 = 0.72
SacramentoRiverBasin EDDI vs. Runoff Index(SRI)
Figures:DanMcEvoy 29
Con
tribu
tions
to c
hang
es
in 1
2-w
eek
E0
(mm
)
Sacramento River basin, CA
(Hobbins et al., JHM 2016)
Example:Droughtintensification(increasingE0)wascausedby:
•First,below-normalHumidity
•Then,increasingTemperature and,toalesserdegree,Radiation
•Windspeed playedlittlerole
Ongoingresearch:Splittingevaporativedemand(E0)intoitsfourmeteorologicaldriverscanhelpdiagnosethecausesofthedemandsideofdrought
Evaporative demand (E0)
Temperature
RadiationHumidity Wind speed
Con
tribu
tions
to c
hang
es
in 1
2-w
eek
E0
(mm
)
Sacramento River basin, CA – February - July 2014
Figure:MikeHobbins 30
WheretogetcurrentEDDImaps
USmaps,alltimewindowsfrom1weekto12months:
EDDIhomepagehttps://www.esrl.noaa.gov/psd/eddi/andclickthe“CurrentConditions” tabOrGoogle:EDDIdrought
RegionalmapsinwesternUS,selectedtimewindows:
CCC-NIDISIntermountainWestDroughtBriefinghttp://climate.colostate.edu/~drought/
WWAClimateDashboardshttp://wwa.colorado.edu/climate/dashboard.htmlhttp://wwa.colorado.edu/climate/dashboard2.html
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WheretogetpastEDDImaps
USmaps,alltimewindowsfrom1weekto12months,from1980topresent.
EDDIhomepage– EDDIMapArchivehttps://www.esrl.noaa.gov/psd/eddi/andclickthe“EDDIMapArchive”tab
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Wheretogethistoricaltime-seriesofEDDI
OtherEDDIdataneeds?Contactmike.hobbins@noaa.gov ordaniel.mcevoy@dri.edu
EDDIhomepagehttps://www.esrl.noaa.gov/psd/eddi/andclickthe“TimeSeries”tabOrGoogle:EDDIdrought
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ForfurthertechnicalbackgroundonEDDI,seethispairofpeer-reviewedpapers
Ifyoucan’taccessthesepapersviatheabovelinks,orneedothertechnicalinformationaboutEDDI,contactcontactmike.hobbins@noaa.gov ordaniel.mcevoy@dri.edu
• M.Hobbins, A.Wood,D.McEvoy,J.Huntington, C.Morton,M.Anderson, andC.Hain(June2016):TheEvaporativeDemandDroughtindex:PartI–LinkingDroughtEvolutiontoVariationsinEvaporativeDemand.Journalof Hydrometeorology,17(6),1745-1761, doi:10.1175/JHM-D-15-0121.1
• D.McEvoy,J.Huntington,M.Hobbins, A.Wood, C.Morton,M.Anderson, andC.Hain(June2016)TheEvaporativeDemandDroughtindex:PartII–CONUS-wideAssessmentAgainstCommonDroughtIndicators.Journalof Hydrometeorology,17(6),1763-1779,doi:10.1175/JHM-D-15-0122.1
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Acknowledgements• TheEDDITeam:JoeBarsugli1,3,CandidaDewes1,4,MikeHobbins1,
JustinHuntington2,JeffLukas3,DanielMcEvoy2,CharlesMorton2,ImtiazRangwala1,3,4,AndreaRay1,3,HeatherYocum1,3
• Fundingandothersupport:
– NationalIntegratedDroughtInformationSystem(NIDIS)– NOAAJointTechnologyTransferInitiative(JTTI)– NOAASectoralApplicationsResearchProgram(SARP)– 1NOAAESRLPhysicalSciencesDivision(PSD)– 2DesertResearchInstitute(DRI)/WesternRegionalClimateCenter
(WRCC)– 3WesternWaterAssessment,CIRES,UniversityofColorado– 4DOINorthCentralClimateScienceCenter
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