The Estimation of Evapotranspiration by Some Equations Under Hot and Arid Conditions

Abstract

ABSTRACT THE most common methods for the estimation of evapotranspiration (ET) were evaluated under a hot and arid climate, by comparing the estimates obtained, with the actual ET from 20 cm tall, well watered and dense cover of alfalfa. The reference ET was measured with steel lysimeters (2 m x 2 m x 1.25 m in size), installed at the Agricultural Research Station of Agriculture College, King Saud University in Dirab (near Riyadh, Saudi Arabia). The climatic data, needed for estimation with the various methods, were taken from the meteorological unit of the Research Station, situated adjacent to the lysimeters. It was found that the summer ET is underestimated by all the methods, namely: Blaney-Criddle (modified), Jensen-Haise, Turc and Hargreaves methods. The winter ET is underestimated by Blaney-Criddle only, while a fair estimate of the winter ET is given by the Turc, Hargreaves and Jensen-Haise methods. Best estimates of ET are obtained with Jensen-Haise method from October to March. To obtain better results with these formulae, a new chart for k^-values of alfalfa was prepared for use with the Blaney-Criddle method and improved coefficients were developed for the Jensen-Haise, Turc and Hargreaves methods. Coefficients were also developed for ET estimation with evaporation from class 'A' pan, under hot and arid conditions.