Research on the climatic dependence of evaporation coefficients

Abstract

Atmospheric evaporative demand ,AED, is defined as the upper limit of evaporation from a natural vegetative surface of which the water content of the soil surface layer is at its current value. AED represents the sum of evaporation from vegetative and soil surfaces of a natural terrestrial surface. It is calculated as the product of evaporation coefficient , kc, and reference crop evaporation, Eo, and is invaluable for estimating the upper limit of crop water requirements. From this the daily soil water content in cropped lands may be computed. Such information is used extensively in practical problem solving, for example by applying the PUTU-system of crop growth models. The accuracy of AED estimated in the aforementioned manner however, depends entirely upon the reliability of kc and the accuracy with which Eo is calculated or measured. Inaccuracies in kc-values cause insufficient or over-irrigation with detrimental financial implications, not only to individual farmers, but for the country in general.

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