Calculated and observed evaporation in a dry monsoonal environment

Abstract

The annual regimes of calculated Penman evaporation, observed evaporation from the standard Australian tank and the Piche evaporimeters and several empirical evaporation predictors from a dry monsoonal environment are described and compared. The relationship between the evaporation predictors and the Penman and tank evaporation is examined. This analysis was carried out with specific reference to selected wet and dry periods of the year, each period being of 100 days' duration. It was found that evaporimeters and Dalton type relations show a slight lag behind Penman evaporation and that the Thornthwaite and Blaney and Criddle estimates are inadequate to describe either the Penman or tank evaporation regime throughout the year in this climatic environment. Marked differences in the efficiency of the various estimates in predicting Penman and tank evaporation over five-day intervals were found. No single relationship could be identified that would satisfy both wet and dry periods of the year. It is concluded that the use of a single generalized relationship in this type of environment for predicting either Penman or tank evaporation from any of the predictors used can only be justified where a high degree of approximation is acceptable.