DAILY SURFACE MOISTURE MODEL FOR LARGE AREA SEMIARID LAND APPLICATION WITH LIMITED CLIMATE DATA

Evapotranspiration and surface soil moisture are seldom monitored on a routine basis like other climatic parameters, and consequently must be modelled from whatever data one may have available. A simple daily model is presented, which uses a modified Priestley-Taylor concept, whereby the alpha term is dynamic, and dependent on the available surface moisture. The relationship between alpha and the surface moisture is a result of the drying character of the soil, and very much a function of whether the surface is bare or vegetation-covered. Also, the soil heat flux is shown to be an important parameter which should not be neglected, and may also be estimated from the surface moisture.