Comparison of methods to calculate evaporation from reservoirs

Large volumes of water evaporate from reservoirs in arid and semi-arid regions. Such water losses are substantial in the regional water balance, and must be considered in the management of water resources. This paper evaluates 12 reservoir evaporation methods that are applied to calculate daily evaporation from Karkheh reservoir (Iran) created by the world’s sixth largest dam. The Bowen ratio energy budget (BREB) formula is chosen as the reference method for the purpose of evaluating 12 alternative evaporation methods. The evaporation methods are ranked based on their accuracy, sensitivity to input variables, and simplicity of application by means of the technique for order of preference by similarity to ideal solution (TOPSIS) multi-criteria decision analysis method. Our results from a multi-year data set for Karkheh reservoir indicate that the best-ranked methods by TOPSIS considering the performance indices are the solar radiation-temperature based methods and the Blaney and Criddle method that is based on temperature and daylight duration variables.