|Soil 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.