Evapotranspiration under Extremely Arid Climates

Abstract

Based on Jensen‐Haise's formula, an equation is recommended for predicting reference evapotranspiration (ETR) under extremely arid conditions. This equation is reached by comparing and evaluating selected estimation methods with results obtained from measured reference evapotranspiration, ETR. Monthly values of ETR are estimated by each of the selected methods using climatic data collected from four observation stations within the area under study. In spite of the satisfactory correlation obtained between values estimated from different methods at the same station as well as the same method in different stations, considerable differences are found in the numerical ETR values suggested by each of these methods. Such differences are very serious when noting that most of these methods are currently used for estimating irrigation water requirements, in many extremely arid areas where the main source of water could be a limited storage of nonrenewable groundwater. In such circumstances future disappointments are sure to be confronted since all of the selected estimation methods indicate much lower ETR values than those obtained by direct measurements.