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.x Branch •No lake model •No blowing snow •No permafrost VIC Model Versions 4.0.3

•No canopy energy balance •Treeline computation •406-style aero_resist •Inconsistent aero_resist reporting •Grnd_flux & deltaH incorrect 4.0.6

•Flexible output config •Output aggregation 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 4.1.0_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 4.1.0_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 4.1.2

•Under development

Updates Since 4.0.6 and 4.1.0: Features from 4.1.0

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 • • •

Parameters

New wfrac parameter replaces max_depth, depth_frac and rate_frac

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

old

Updates Since 4.0.6 and 4.1.0: Features from 4.1.0

Linear

Permafrost Enhancements

Global Param Options • IMPLICIT = implicit solver • EXP_TRANS = exponential node spacing Exponential User_def.h Options • EXCESS_ICE

 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 (smooth/shallow) OUT_PET_SHORT OUT_PET_TALL Water Surface Short Reference Crop Tall Reference Crop OUT_PET_NATVEG moisture limitation Natural Vegetation, no soil OUT_PET_VEGNOCR Natural Veg. with Rc = 0

SatSoil > H2OSurf (rougher) Trans is near NatVeg when soil is wet ECan + Trans > Most PETs VegNoCR is usually highest Trans declines as soil dries

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?

Arctic location, 15 Nodes, Linear distribution, Dp=4m, Constant Tb, explicit scheme Original TFALLBACK By the time convergence failure occurs, it’s

too late

Problem actually occurred much earlier – “cold nose” at 2 nd 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 = 20m Exponential Node Distrib NOFLUX bottom boundary Explicit scheme Effect on surface T is small Effect 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

COMPUTE_TREELINE omit)

GF_410

FALSE (or JULY_TAVG_SUPPLIED MIN_LIQ

PLAPSE

FALSE (or omit) FALSE (or omit)

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_406 GRND_FLUX_TYPE

IMPLICIT EXP_TRANS EQUAL_AREA

GF_406

FALSE (or omit) FALSE (or omit) FALSE (or omit) LAKES LAKE_PROFILE BLOWING MIN_LIQ

PLAPSE

FALSE (or omit) FALSE (or omit) FALSE (or omit) FALSE (or omit)

FALSE

SNOW_ALBEDO SNOW_DENSITY USACE (or omit) DENS_BRAS (or omit) • User_def.h Options (compile-time)

CLOSE_ENERGY FALSE SPATIAL_FROST SPATIAL_SNOW FALSE FALSE EXCESS_ICE FALSE

New Web Site

www.hydro.washington.edu/Lettenmaier/Models/VIC/new/ • Under Construction • Up-to-date Documentation • Consolidation / Reorganization • Easier Navigation • Suggestions?

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?