Describe processes represented by the model
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Land Cover and Soil Snow Model
Meteorology (Inputs, Distributed Precip, and Snow/Elevation Bands)
Frozen Soil (including Permafrost)
Dynamic Lake/Wetland Model (new to 4.1.1)
Flow Routing
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Describe key physical parameters and equations
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Land Cover can subdivide each grid cell's land cover into arbitrary number of "tiles", each corresponding to the fraction of the cell covered by that particular land cover (e.g. coniferous evergreen forest, grassland, etc.)
geographic locations or configurations of land cover types are not considered; VIC lumps all patches of same cover type into 1 tile
Snow Model
VIC considers snow in several forms: ground snow pack, snow in the vegetation canopy, and snow on top of lake ice. Main features:
Ground snow pack is quasi 2-layer; the topmost portion of the pack is considered separately for solving energy balance at pack surface
Meteorological Input Data
Can use sub-daily met data (prcp, tair, wind) at intervals matching simulation time step
Can use daily met data (prcp, tmax, tmin, wind) for daily or sub-daily simulations
Disaggregates daily met data to sub-daily via Thornton & Running algorithm and others (computes incoming sw and lw rad, pressure, density, vp)
VIC can consider spatial heterogeneity in precipitation, arising from either storm fronts/local convection or topographic heterogeneity. Here we consider the influence of storm fronts and local convective activity. This functionality is controlled by the DIST_PRCP option in the global parameter file. Main features:
Can subdivide the grid cell into a time-varying wet fraction (where precipitation falls) and dry fraction (where no precipitation falls).
The wet fraction depends on the intensity of the precipitation; the user can control this function.
Fluxes and storages from the wet and dry fractions are averaged together (weighted by area fraction) to give grid-cell average for writing to output files.
Elevation Bands
VIC can consider spatial heterogeneity in precipitation, arising from either storm fronts/local convection or topographic heterogeneity. Here we consider the influence of topography, via elevation bands. This is primarily used to produce more accurate estimates of mountain snow pack. This functionality is controlled by the SNOW_BAND option in the global parameter file. Main features:
Can subdivide the grid cell into arbitrary number of elevation bands, to account for variation of topography within cell
Within each band, meteorologic forcings are lapsed from grid cell average elevation to band's elevation
Geographic locations or configurations of elevation bands are not considered; VIC lumps all areas of same elevation range into 1 band
Fluxes and storages from the bands are averaged together (weighted by area fraction) to give grid-cell average for writing to output files
However, the band-specific values of some variables can be written separately in the output files
Liang et al. (1999): set QUICK_FLUX to TRUE in global parameter file; this is the default for FULL_ENERGY = TRUE and FROZEN_SOIL = FALSE.
Cherkauer et al. (1999): set QUICK_FLUX to FALSE in global parameter file; this is the default for FROZEN_SOIL = TRUE.
By default, the finite difference formulation is an explicit method.
By default, the nodes of the finite difference formulation are spaced linearly.
These apply to the case QUICK_FLUX = FALSE and FROZEN_SOIL = TRUE, i.e. the formulation of Cherkauer et al. (1999).
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