A Simple Model for Predicting Evaporation from Bare Soils

A phenomenological model is described for predicting evaporation from bare and freely drained soils with a deep water table. The model delineates three classical and one transitional drying stage as the drying front advances into the soil profile. Daily evaporation is estimated from the daily potential evaporation rate e₀ and depth of the drying front, Z, reached at the start of the day. The approximating relations used for calculating soil evaporation rate as a function of advancing drying front under different drying stages are presented. Input parameters of the model are simple and easily measurable under field conditions viz. daily potential evaporation rate, wilting point and field capacity moisture contents. Predictions of the model were tested using published data for cumulative evaporation. Good agreement was obtained under widely varying evaporative conditions. The model is simple and practical and may be used even for remote areas where the detailed information on soil water retention and transmission characteristics is not available.