Different Methods for Evaluating of Evaporation Losses From the Open Water Surface in Semi-Arid Area of Gujarat, India

Evaporation from water surfaces as an essential component of the water balance has long been of interest to hydrologists and water economists. Determining evaporation rates is essential for efficient management of reservoirs and water resources, particularly in water-scarce countries such as North Gujarat and Saurashtra region in India. While evaporation loss is of significant concern, the threat of a changing climate has been directing greater focus to how much water will be lost from India’s reservoirs in the future. The estimates of eight methods namely Penman, Modified Penman, Meyer’s, Rohwer’s, Papadakis, Blaney-Criddle, Hamon and Thorntwaite for calculating evaporation were compared with pan evaporation for the study area as Dharoi reservoir, North Gujarat, India. The comparisons were based on monthly, yearly and seasonal evaporation basis. All the methods gave comparable estimates of evaporation for spring and summer months. The comparison of monthly values indicated that the estimated of evaporation by Hemon and modified Penman gave better correlation with pan values for most of the months. Several of the methods had substantial bias when compared with Pan Values and were subsequently modified to eliminate bias. Methods that rely only on measurement of air temperature, or air temperature and solar radiation, were relatively cost-effective options for measuring evaporation at this Dharoi reservoir, outperforming some methods that require measurement of a greater number of variables.