Comparison of two computer models for predicting soil water in a tropical monsoon climate

Abstract A physical soil water model, based on Darcy's Law and the continuity equation, and a water budget model were tested for three crops grown in the humid coastal zone of northeastern Brazil. Both models required daily information on precipitation, class A pan evaporation, and used Soil Conservation Service curves to estimate runoff. Crop canopy and rooting characteristics, needed on a daily basis, were similar for both models. Both models predicted soil water contents that compared favorably with measured values, and predicted evapotranspiration and drainage were probably superior to estimates from water balance calculations based on periodic measurements of soil water content and suction. The water budget model would have been improved if the “field capacity” had been based on the highest measured water contents in the rainy season. The models were more sensitive to rooting depth than to root distribution. Rate of canopy development had little effect on predicted drainage and evapotranspiration, but significantly changed the ratio of evaporation to transpiration.