Investigating the Effects of Climate Change on Daily Evapotranspiration in Models with Different Mathematical Structures in Various Climates of Iran

Climate change affects the hydrological processes through changes in temperature, precipitation, and other climate variables. One of the most important consequences of climate change is its impact on agricultural water consumption, which can seriously address water resources management. The purpose of this study was to investigate the effects of climate change on daily evapotranspirationin different climates across Iran. For this purpose, the minimum, and maximum temperature, as well as precipitation, and sunshine hours were simulated for the period 2016-2036 on the A1B, A2 and B1a scenarios using the HadCM3 general circulation model and weather generator (LARS-WG 5.5) on daily time scale. The results indicated increase in temperature and evapotranspiration and decrease in precipitation in different climates. In another section of this study, by comparing the empirical equations, it was concluded that Hargreaves method with high R2, fair NS, and lower values of RMSE and MAE compared to other methods, can be an appropriate alternative for the FAO Penman-Monteith method on daily scale. For example, the results for Birjand station were R2 = 0.59, NS = 0.53, RMSE 6.84 and MAE = 6.01. Finally, Hargreaves- Samani and the Makkink methods had the least accuracy in estimating the reference evapotranspiration. Therefore, Hargreaves method can be selected as the best alternative method for estimating the reference evapotranspiration on a daily basis.