Calibration of empirical equations for estimating reference evapotranspiration in different climates of Iran

The accurate estimation of reference evapotranspiration (ETref) is a crucial component for modeling hydrological and ecological cycles. goal this study was the calibration 32 empirical equations used to determine ETref in three classes temperature-based, solar radiation–based, mass transfer–based evapotranspiration. based on measurements taken between years 1990 2019 at 41 synoptic stations located very dry, semidry, humid climates Iran. performance original calibrated compared PM-FAO56 equation evaluated model evaluation techniques including coefficient determination (R2), root mean square error (RMSE), average percentage (APE), bias (MBE), index agreement (D), scatter (SI). results show that Baier Robertson temperature-based models, Jensen Haise radiation–based Penman models performed better than equations. had, respectively, an R2 = 0.73, 0.67, 0.78; RMSE 35.14, 35.02, 30.20 mm year-1; MBE ? 5.6, 3.89, 2.57 year-1. had values 0.60, 0.37, 0.65; 68.34, 66.98, 52.62 5.75, 4.26, 8.99 year-1, respectively. dry climate (e.g., Zabol, Zahedan, Bam, Iranshahr, Chabahar stations) also significantly reduced SI value from > 0.3 (poor class) < 0.1 (excellent class). Therefore, are highly recommended estimating different climates.