VIC Soil Parameter File¶
The soil parameter file serves three main purposes:
- Define the cell ID number of each grid cell. This ID number is essentially a database key that links a grid cell to its parameters in the various parameter files.
- Define the grid cell soil parameters, as well as geographic information such as grid cell center latitude and longitude.
- Define initial soil moisture conditions, to be used in the absence of an initial state file.
The soil parameters are supplied to VIC as a single ASCII file, with a separate row for each grid cell, with each field containing a different parameter value (description of this file is below).
Soil hydrologic and thermal parameters needed for the different VIC model set-ups are listed below. All columns of the input file must be filled, but certain parameters need only be defined if the full energy or frozen soil models are activated. Variables in Red only need to have meaningful values if FULL_ENERGY
is TRUE
, otherwise they will be ignored (but a placeholder value of -9999 must still be present in that field unless the documentation explicitly says the field is optional). Violet text indicates parameters needed for the frozen soil model. Header lines can be added by starting the line with a '#'.
In previous versions certain parameters were read as average values for the entire soil column. In version 4.0 all soil parameter values are now read for all layers. Converting the soil parameter file from older model versions, should simply require copying column average values to separate columns for each soil moisture layer.
To help in understanding this file, an example file has been attached at the bottom of this page.
Column | Variable Name | Units | Number of Values | Description |
---|---|---|---|---|
1 | run_cell | N/A | 1 | 1 = Run Grid Cell, 0 = Do Not Run |
2 | gridcel | N/A | 1 | Grid cell number |
3 | lat | degrees | 1 | Latitude of grid cell |
4 | lon | degrees | 1 | Longitude of grid cell |
5 | infilt | N/A | 1 | Variable infiltration curve parameter (binfilt) |
6 | Ds | fraction | 1 | Fraction of Dsmax where non-linear baseflow begins |
7 | Dsmax | mm/day | 1 | Maximum velocity of baseflow |
8 | Ws | fraction | 1 | Fraction of maximum soil moisture where non-linear baseflow occurs |
9 | c | N/A | 1 | Exponent used in baseflow curve, normally set to 2 |
10 : (Nlayer+9) | expt | N/A | Nlayer | Exponent n (=3+2/lambda ) in Campbell's eqn for hydraulic conductivity, HBH 5.6 (where lambda = soil pore size distribution parameter). Values should be > 3.0. |
(Nlayer+10):(2*Nlayer+9) | Ksat | mm/day | Nlayer | Saturated hydrologic conductivity |
(2*Nlayer+10):(3*Nlayer+9) | phi_s | mm/mm | Nlayer | Soil moisture diffusion parameter |
(3*Nlayer+10):(4*Nlayer+9) | init_moist | mm | Nlayer | Initial layer moisture content |
(4*Nlayer+10) | elev | m | 1 | Average elevation of grid cell |
(4*Nlayer+11):(5*Nlayer+10) | depth | m | Nlayer | Thickness of each soil moisture layer |
(5*Nlayer+11) | avg_T | C | 1 | Average soil temperature, used as the bottom boundary for soil heat flux solutions |
(5*Nlayer+12 | dp | m | 1 | Soil thermal damping depth (depth at which soil temperature remains constant through the year, ~4 m) |
(5*Nlayer+13):(6*Nlayer+12) | bubble | cm | Nlayer | Bubbling pressure of soil. Values should be > 0. |
(6*Nlayer+13):(7*Nlayer+12) | quartz | Nlayer | Quartz content of soil | |
(7*Nlayer+13):(8*Nlayer+12) | bulk_density | kg/m3 | Nlayer | Bulk density of soil layer |
(8*Nlayer+13):(9*Nlayer+12) | soil_density | kg/m3 | Nlayer | Soil particle density, normally 2685 kg/m3 |
(Optional) | organic | fraction | Nlayer | Fraction of soil layer that is organic. If ORGANIC_FRACT is TRUE in the global parameter file, this variable must be included in the soil parameter file. If ORGANIC_FRACT is FALSE then this variable must not appear in the soil parameter file. (release 4.1.2 and later) |
(Optional) | bulk_dens_org | kg/m3 | Nlayer | Bulk density of organic portion of soil. If ORGANIC_FRACT is TRUE in the global parameter file, this variable must be included in the soil parameter file. If ORGANIC_FRACT is FALSE then this variable must not appear in the soil parameter file. (release 4.1.2 and later) |
(Optional) | soil_dens_org | kg/m3 | Nlayer | Soil particle density of organic portion of soil, normally 1300 kg/m3. If ORGANIC_FRACT is TRUE in the global parameter file, this variable must be included in the soil parameter file. If ORGANIC_FRACT is FALSE then this variable must not appear in the soil parameter file. (release 4.1.2 and later) |
(9*Nlayer+13) | off_gmt | hours | 1 | Time zone offset from GMT. This parameter determines how VIC interprets sub-daily time steps relative to the model start date and time. NOTE: Important update in VIC 4.1.2: We have adopted the following convention for off_gmt: 0 indicates that the model start date/time is relative to Greenwich Mean Time (GMT). grid_cell_longitude*24/360 ) indicates that the model start date/time is relative to local time. off_gmt=0 means VIC results are referenced to GMT; off_gmt=(grid_cell_longitude*24/360) means VIC results are referenced to local time). Therefore, if mixing daily and sub-daily forcing inputs, it is important that any sub-daily forcing inputs be shifted as necessary to be in the time zone indicated by off_gmt. |
(9*Nlayer+14):(10*Nlayer+13) | Wcr_FRACT | fraction | Nlayer | Fractional soil moisture content at the critical point (~70% of field capacity) (fraction of maximum moisture) |
(10*Nlayer+14):(11*Nlayers+13) | Wpwp_FRACT | fraction | Nlayer | Fractional soil moisture content at the wilting point (fraction of maximum moisture) |
(11*Nlayer+14) | rough | m | 1 | Surface roughness of bare soil |
(11*Nlayer+15) | snow_rough | m | 1 | Surface roughness of snowpack |
(11*Nlayer+16) | annual_prec | mm | 1 | Average annual precipitation. |
(11*Nlayer+17):(12*Nlayer+16) | resid_moist | fraction | Nlayer | Soil moisture layer residual moisture content in units of residual moisture content volume / total layer volume [mm/mm]. |
(12*Nlayer+17) | fs_active | 1 or 0 | 1 | If set to 1, then frozen soil algorithm is activated for the grid cell. A 0 indicates that frozen soils are not computed even if soil temperatures fall below 0C. |
(Optional) | frost_slope | C | 1 | Slope of uniform distribution of soil temperature (if SPATIAL_FROST == TRUE in the global parameter file). |
(Optional) | max_snow_distrib_slope | m | 1 | Maximum slope of the snow depth distribution. This is only used if SPATIAL_SNOW == TRUE in the global parameter file. This parameter should be set to twice the spatial average snow depth at which coverage == 1.0. In other words, if we define depth_thresh to be the minimum spatial average snow depth below which coverage < 1.0, then max_snow_distrib_slope = 2depth_thresh. NOTE: Partial snow coverage is only computed when the snow pack has started melting* and the spatial average snow pack depth <= max_snow_distrib_slope/2 . During the accumulation season, coverage is 1.0. Even after the pack has started melting and depth <= max_snow_distrib_slope/2 , new snowfall resets coverage to 1.0, and the previous partial coverage is stored. Coverage remains at 1.0 until the new snow has melted away, at which point the previous partial coverage is recovered. |
(Optional) | July_Tavg | C | 1 | Average July air temperature, used for treeline computations (required if COMPUTE_TREELINE == TRUE in the global parameter file). |
Note: if BASEFLOW is set to NIJSSEN2001 in the global parameter file, VIC will interpret the baseflow parameters Ds, Dsmax, Ws, and c to be the alternative baseflow parameters D1, D2, D3, and D4.
Example Soil Parameter File:¶
Example Soil Parameter File: VIC 4.0.5/4.0.6 Water Balance
#RUN GRID LAT LNG INFILT Ds Ds_MAX Ws C EXPT_1 EXPT_2 EXPT_3 Ksat_1 Ksat_2 Ksat_3 PHI_1 PHI_2 PHI_3 MOIST_1 MOIST_2 MOIST_3 ELEV DEPTH_1 DEPTH_2 DEPTH_3 AVG_T DP BUBLE1 BUBLE2 BUBLE3 QUARZ1 QUARZ2 QUARZ3 BULKDN1 BULKDN2 BULKDN3 PARTDN1 PARTDN2 PARTDN3 OFF_GMT WcrFT1 WcrFT2 WcrFT3 WpFT1 WpFT2 WpFT3 Z0_SOIL Z0_SNOW PRCP RESM1 RESM2 RESM3 FS_ACTV JULY_TAVG
1 7 43.739 -92.4.0 0.010 1.e-4 3.05 0.93 2 4.0 4.0 4.0 250.0 250.0 250.0 -999 -999 -999 0.4 0.4 0.4 306.3 0.1 6.90 2.000 14.0 4.0 75.0 75.0 75.0 0.24 0.24 0.24 1306 1367 1367 2650 2650 2650 -6 0.330 0.330 0.330 0.133 0.133 0.133 0.001 0.010 500 0.02 0.02 0.02 1 18.665