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?