Comparative analysis of 12 reference evapotranspiration methods for semi-arid regions (Spain)

Evapotranspiration is one of the most significant variables used to determine runoff, hydrological balances, and climate change studies. In semi-arid conditions, there is a need to evaluate various alternatives to establish reference evapotranspiration (ETo), given that climate change scenarios sometimes do not provide information on diverse climate variables. Several alternatives for obtaining evapotranspiration are analyzed in this study and compared with the Penman-Monteith method, modified by FAO (PMFAO56). Due to limited daily climate information, it is necessary to consider different options for determining reference evapotranspiration. In the present work, methods based on temperature (Hargreaves, Hargreaves 1, Hargreaves 2, and Baier-Robertson) and radiation (Caprio, Irmark 1, Irmark 2, Irmark 3, Makkink, Priestley-Taylor and Hasen) were investigated. The best performance for the semi-arid Jucar River Basin was determined by Hargreaves methods. Regional calibration of Hargreaves methods, Hargreaves 1 and Hargreaves 2, were performed for each sub-basin.