what’s new in vic 4.1.1
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What’s New in VIC 4.1.1. Ted Bohn Hydro Seminar June 23, 2009. Outline. What is VIC 4.1.1, Anyway? Updates since 4.0.6 and 4.1.0 Features from 4.1.0 Features from 4.0.6 Completely New Backwards-compatibility New VIC Web Site VIC Needs Your Help! Testing VIC How To Get 4.1.1 - PowerPoint PPT PresentationTRANSCRIPT
What’s New in VIC 4.1.1
Ted Bohn
Hydro Seminar
June 23, 2009
Outline
• What is VIC 4.1.1, Anyway?• Updates since 4.0.6 and 4.1.0
– Features from 4.1.0– Features from 4.0.6– Completely New– Backwards-compatibility
• New VIC Web Site • VIC Needs Your Help!
– Testing VIC– How To Get 4.1.1
• Future Possibilities
What is VIC 4.1.1, Anyway?
• Successor to both 4.0.6 and 4.1.0– 4.0.6 and 4.1.0 are not compatible– Some of 4.1.0’s new features broke some of
the older features– 4.1.1 has “best” of both versions– 4.1.1 can (mostly) reproduce results of 4.0.6
and 4.1.0
• 4.1.1 has further improvements
4.0.34.0.x Branch•No lake model•No blowing snow•No permafrost•No canopy energy balance•Treeline computation•406-style aero_resist•Inconsistent aero_resist reporting•Grnd_flux & deltaH incorrect
4.1.0_x Branch•Lake/wetland model•Blowing snow•Canopy energy balance•No treeline computation•410-style aero_resist•Inconsistent aero_resist reporting•Grnd_flux correct•deltaH & fusion incorrect
4.0.6•Flexible output config•Output aggregation
4.1.0_r4•Lakes v.1•24h water balance errors•Flexible output config•Output aggregation
4.1.0_r5•Lakes v.2•Fixed 24h water balance•Permafrost Enhancements
4.1.1•Treeline computation•Lakes v.2•Blowing snow•Canopy energy balance•Permafrost Enhancements•406-style aero_resist•Consistent aero_resist reporting•Frozen soil bug fixes•Correct grnd_flux, deltaH, and fusion•Air pressure lapsing option•Snow pack improvements
4.1.2•Under development
VIC Model Versions
Updates Since 4.0.6 and 4.1.0:Features from 4.1.0
Parameters• New wfrac parameter replaces max_depth, depth_frac and rate_frac – old
parameter files won’t work• Set LAKES to lake parameter file name in global param file• Optionally specify lake basin shape in lake parameter file
Dynamic Lake/Wetland Model (Bowling, 2002, 2009)•Multi-layer lake model of Hostetler et al. 2000
•Energy-balance model•Mixing, radiation attenuation, variable ice cover
•Dynamic lake area (taken from topography) allows seasonal inundation of adjacent wetlands•Currently not part of channel network
Updates Since 4.0.6 and 4.1.0:Features from 4.1.0
Permafrost EnhancementsGlobal Param Options• IMPLICIT = implicit solver• EXP_TRANS = exponential
node spacing
User_def.h Options• EXCESS_ICE
Dep
th
Linear Exponential
Excess Ground Ice and Subsidence Algorithm:
excess ice is the concentration of ice in excess of what the soil can hold were it unfrozen – we define it as n’-n, where n’ is the expanded soil porosity, and n is the unfrozen soil porosity
as excess ice in a soil layer melts (see example at left), the ground subsides
for the below runs, we utilize 8 soil layers, ranging in thickness from 0.1 to 0.6 m
Updates Since 4.0.6 and 4.1.0:Features from 4.1.0
Soil T heterogeneity: “Spatial Frost”• Linear (uniform) distribution of soil T around mean• Allows some moisture movement in soil when avg T below
freezing
• Requires extra soil parameter: frost_slope
• User_def.h (compile-time) option:– Set SPATIAL_FROST to
TRUE– Set FROST_SUBAREAS
(number of frost “bands”)
Cherkauer et al. (2003)
Updates Since 4.0.6 and 4.1.0:Features from 4.1.0
Partial Snow Cover: “Spatial Snow”• If melting & avg SWE < depth_full_snow_cover, snow
coverage is proportional to SWE• Requires extra soil parameter: depth_full_snow_cover• User_def.h (compile-time) option:
– Set SPATIAL_SNOW to TRUE
Updates Since 4.0.6 and 4.1.0:Features from 4.1.0
Canopy Energy Balance• Separate canopy temperature• Radiative fluxes between canopy and ground/snowpack
surface• Can iterate between surface and canopy solutions for
total balance:– Set CLOSE_ENERGY to TRUE in user_def.h (compile-time
option)
Blowing Snow• Blowing snow sublimation• Set BLOWING to TRUE in global param file
Updates Since 4.0.6 and 4.1.0:Features from 4.0.6
24h water balance mode• Snow step was broken in 4.1.0 – now is fixed
Treeline Computation• Use in conjunction with snow/elevation bands• Uses avg July T of forcings to determine which bands are above
treeline• Above treeline, replaces any overstory veg tiles with non-overstory
veg cover• Otherwise, runaway snowpack (“glaciers”)• Set COMPUTE_TREELINE to a veg class ID number in global
param file (ID number of non-overstory class)• JulyAvgT can be supplied in soil file instead of computed from
forcings:– Set JULY_TAVG_SUPPLIED to TRUE in global param file
Updates Since 4.0.6 and 4.1.0:Completely New
Potential ET
• 6 Types of PET can now be output:OUT_PET_SATSOIL Saturated Soil
OUT_PET_H2OSURF Water Surface (smooth/shallow)
OUT_PET_SHORT Short Reference Crop
OUT_PET_TALL Tall Reference Crop
OUT_PET_NATVEG Natural Vegetation, no soil moisture limitation
OUT_PET_VEGNOCR Natural Veg. with Rc = 0
VegNoCR is usually highest
Trans declines as soil dries
ECan + Trans > Most PETs
Trans is near NatVeg when soil is wet
SatSoil > H2OSurf(rougher)
Updates Since 4.0.6 and 4.1.0:Completely New
T instability handling• In past, soil T solution often failed to converge in arctic
climates• Jenny Adam’s permafrost enhancements solved most
problems• Just in case, we now have better error handling:
CONTINUEONERROR in global param file– FALSE: VIC exits completely when a grid cell encounters T
failure– TRUE: VIC moves to next grid cell when T failure occurs– TFALLBACK: use previous timestep’s T value and continue with
current grid cell• Applies to surface and canopy T solutions as well• NOTE: by the time the solution fails to converge, T values may have
been unreasonable for days or weeks
How effective is the TFALLBACK option?
Original
TFALLBACK
By the time convergence failure occurs, it’s too late
Arctic location, 15 Nodes, Linear distribution, Dp=4m, Constant Tb, explicit scheme
Problem actually occurred much earlier – “cold nose” at 2nd deepest node
Implicit scheme also fails…
Other options…Deepening Dp to 20m fixes problem
Node spacing appears to be an issue
But constant Tb at 4m is unrealistic here
Other options…Dp = 20mExponential Node DistribNOFLUX bottom boundaryExplicit scheme
Effect on surface T is smallEffect at depth is large
Implicit scheme may be more accurate/stable, but takes > 10 times longer!
Note: node depths are different from linear case, except for T0 and T14
Updates Since 4.0.6 and 4.1.0:Completely New
Aerodynamic Resistance in Snow-filled Canopy• 4.0.6 and 4.1.0 handled differently; neither was correct• New global param option: AERO_RESIST_CANSNOW
– AR_406: multiply Ra by 10 but only apply to latent heat– AR_406_LS: mult. by 10 and apply to both latent and sensible– AR_406_FULL: same as AR_406_LS but also use canopy Ra
(no correction) when no snow– AR_410: apply stability correction to both L and S– AR_COMBO: apply stability correction and multiply by 10
• 410 accumulates more canopy snow than 406 due to higher Ra; 411 similar to 406 but lower sensible heat
Updates Since 4.0.6 and 4.1.0:Completely New
Ground Flux• 4.0.6 and 4.1.0 handled differently; 4.1.0 more
correct but not perfect• New global param option: GRND_FLUX_TYPE
– GF_406: use (flawed) formulas for grnd_flux, deltaH, and fusion
– GF_410: use correct formula for grnd_flux (Liang et al 1999) but deltaH and fusion don’t take surf_atten into account
– GF_FULL: use correct formula for grnd_flux and take surf_atten into account in deltaH and fusion
• 410 and 411 have larger grnd_flux than 406
Updates Since 4.0.6 and 4.1.0:Completely New
Snow Albedo• New global param file option: SNOW_ALBEDO
– USACE (default): previous algorithm, from US Army Corps; prescribed date of beginning of melt season (optimized for US)
– SUN1999: melt condition = function of cold content only (applicable globally)
Snow Density• New global param file option: SNOW_DENSITY
– DENS_BRAS (default): previous algorithm, taken from Bras (1992)
– DENS_SNTHRM: algorithm taken from SNTHRM model
• No computations depend on snow density, but good for validation of model results against observations
Updates Since 4.0.6 and 4.1.0:Completely New
Pressure Lapsing• Previously, when P and density computed during forcing
disaggregation, set to constant 400m-elevation values– P and density were lapsed to cell or band elevation for canopy
evap & transpiration calculations– But sensible heat used un-lapsed values– Cold bias at high elevations, warm bias at low elevations– Magnitude of effect unknown
• New global param option: PLAPSE– FALSE: previous behavior– TRUE (default): lapse pressure to grid cell average elevation
Updates Since 4.0.6 and 4.1.0:Backwards Compatibility
Compatibility with 4.1.0
• Global Param Options (run-time)AERO_RESIST_CANSNOW AR_410
GRND_FLUX_TYPE GF_410
COMPUTE_TREELINE FALSE (or omit)
JULY_TAVG_SUPPLIED FALSE (or omit)
MIN_LIQ FALSE (or omit)
PLAPSE FALSE
Updates Since 4.0.6 and 4.1.0:Backwards Compatibility
Compatibility with 4.0.6• Global Param Options (run-time)AERO_RESIST_CANSNOW AR_406GRND_FLUX_TYPE GF_406IMPLICIT FALSE (or omit)EXP_TRANS FALSE (or omit)EQUAL_AREA FALSE (or omit)LAKES FALSE (or omit)LAKE_PROFILE FALSE (or omit)BLOWING FALSE (or omit)MIN_LIQ FALSE (or omit)PLAPSE FALSESNOW_ALBEDO USACE (or omit)SNOW_DENSITY DENS_BRAS (or omit)
• User_def.h Options (compile-time)CLOSE_ENERGY FALSESPATIAL_FROST FALSESPATIAL_SNOW FALSEEXCESS_ICE FALSE
New Web Site
• Under Construction• Up-to-date
Documentation• Consolidation /
Reorganization• Easier Navigation• Suggestions?
www.hydro.washington.edu/Lettenmaier/Models/VIC/new/
VIC Needs Your Help!
“Beta” testing• Two questions:
1. Can 4.1.1 reproduce older results with appropriate settings?2. How much different is 4.1.1 with default settings?
• Use your current VIC setup:– Run current VIC– Run VIC 4.1.1 with backwards-compatibility settings– Run VIC 4.1.1 with defaults
• Compare these at a single grid cell– R script
• Compare hydrographs if appropriate• How to get VIC 4.1.1 & R scripts
ftp.hydro.washington.edu/pub/tbohn/vic_code/
Future Possibilities
Model Physics• Wind profile• VPD biases• Enthalpy formulation• Distributed Water Table• Carbon• Lakes with channel inflows• “Image” mode
Future Possibilities
Model Organization• Fewer options
– How many of the current options are really used?– Some new options are intended to be temporary
• Simpler code (data structure overhaul)– Related to options
• Separate initial conditions from parameters• Graphical Interface?