The Use of a Modified Penman Method for Estimating Evapotranspiration in a Hot and Arid Climate PDF

Keywords

Penman method, evapotranspiration, King Saud University

Abstract

To evaluate the modified Penman method of determining evapotranspiration, actual evapotranspiration was measured from an actively growing, 20 cm tall, full cover and well watered crop of alfalfa at the King Saud University Agricultural Experiment Station in Dirab, in 1981 and 1982. Since the modified Penman equation involves variations in the use of coefficients and methods for the calculation of vapor pressure deficit, estimated values of evapotranspiration (ET), with the equation, were determined separately for each method. The meteorological data were taken from an adjacent weather station. The methods suggested by Walker and Wright were found to give close results to the ET from 20 cm tall alfalfa. Suitable wind coefficients are needed with the other methods to get reliable estimates of the ET. Using the actual data from ET, the wind function was derived in each case. WInd coefficients were then determined from the relationship of the wind function to the actual wind run. These coefficients can be used for obtaining more reliable estimates of ET in hot and arid regions in general and Saudi Arabia in particular