VIC Model - Soil Texture¶
Sample Index of Soil Hydraulic Properties*¶
|USDA Class||Soil Type||% Sand||% Clay||Bulk Density||Field Capacity||Wilting Point||Porosity||Saturated Hydraulic Conductivity||Slope of Retention Curve (in log space)
* Source is "Average hydraulic properties of ARS soil texture classes," draft dated February, 2000 by J. Schaake. This expanded the work of others and included a total of 2128 soil samples. Wilting point is the fractional water content at 15 bar tension; field capacity is the fractional water content at 1/3 bar tension.
b is as used in Campbell's equation. ref: Cosby et al., A Statistical exploration of the relationships of soil moisture characteristics to the physical properties of soils, Water Resources Research 20(6): 682-690, 1984.
Note that units in this table differ from those used in the VIC model. In particular:
- Bulk Density for the VIC model should be in kg/m3 (g/cm3 * 1000 = kg/m3
- Field Capacity and Wilting Point for the VIC model are described as a fraction of the maximum moisture, where the maximum moisture for each soil layer is the depth times the porosity. This can be obtained from the above data in cm3/cm3 by dividing the values by the fractional porosity in the table.
- Saturated Hydraulic Conductivity for the VIC model is in mm/day (cm/hr * 240 = mm/day)
- By default, VIC uses the Brooks-Corey relationship for unsaturated flow. The Brooks-Corey exponent, n, can be estimated from the slope of the Retention Curve (in log space), b, in the table above by:
n = 3 + 2b