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United States Department of Agriculture

Agricultural Research Service

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Soil Moisture and Curve Number
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AnnAGNPS Pollutant Loading Model

P. Green BulletSoil Moisture and Curve Number


Daily soil moisture accounting considers runoff, evapotranspiration, and percolation in maintaining a water budget for the 2-layer soil system. Runoff is calculated using the curve number method. Curve numbers vary between the Antecedent Moisture Condition (AMC I --dry) value and the AMC III (wet) value using the procedure in the SWRRB and EPIC models. Potential evapotranspiration is calculated with the Penman equation, and actual evapotranspiration is a function of this and soil moisture content. Percolation occurs at the rate of the hydraulic conductivity corresponding to the soil moisture content, calculated according to the Brooks-Corey equation.


Dave Garen

Last Modified: 8/12/2016
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