عنوان مقاله [English]
Iran is in arid and semi-arid belt in world, which is characterized by low rainfall, heavy rainfall, flood flows and high evapotranspiration. So, quantitative evaluation of evapotranspiration on a regional scale is necessary for water resources management, crop production and environmental assessments in irrigated lands. In this study, in order to estimate ETo in four synoptic stations with arid, semi-arid, humid and semi-humid climate, from meteorological data such as: temperature, net radiation, relative humidity and wide velocity were used. Reference evapotranspiration was calculated using 5 different methods, including Hargreaves-Samani, Blaney-Criddle, Priestly-Tailor, Turc and Makkink, besides, the standard FAO-56 was used (because there was no Lysimetric data in the region) to evaluate the applied formulas. In order to evaluate these methods, used the mean absolute error (MAE), root mean squared error (RMSE), normal root mean square error (NRMSE), mean bias error (MBE), correlation coefficient (r), Nash -Satclif index (N.S). Based on these indices, Belaney-Criddle method, following the FAO-56 method as the basis, with correlation coefficient (0.99), RMSE (0.11-0.14), negative MBE, which represents less estimation than observational data, and the Nash-Sutcliffe equal to one as the first method for the four distinct climates in Iran (Rasht station with wet climate, Urmia station with semi-humid climate, Yazd station with dry climate and Mashhad station with semi-arid climate). The Blaney-Criddle method was chosen as the best method for these regions because of its higher correlation coefficient and lower root mean square error than the other evapotranspiration estimation methods used in this study.