Testing and Modification of Penman's Evaporation Model for Estimating Class A Pan Evaporation for Udaipur Region, India*

Abstract

Evaporation from the surface of the earth to the atmosphere concerns workers from a wide range of disciplines. Although much theoretical study and experimental work have been done in this direction, there is still much scope in this field. None of the methods to determine the rate of evaporation have yet produced a complete answer that meets the need of engineers and others requiring quantitative results. This paper summarises the test results of evaporation rate obtained by using the original evaporation model developed by Penman and also the results obtained by the modified model. It was found that the results obtained by use of the modified model were very close to the observed values of the evaporation measured by USWB Class A Pan. Results indicated that variations between the estimated and observed rates of evaporation were -7.55%, -26.81%, -5.29% and -13.45% for Rabi, Summer, Kharif and yearly estimates respectively while using the original model. After modification, the variations between the estimated and observed rate of evaporation were found to be +2.96%, -9.89%, +5.64% and -0.86% respectively for the above mentioned periods. The test results showed that the modified model could be used with a higher degree of confidence in Udaipur region of India.