Comparison of the performances of six empirical mass transfer-based reference evapotranspiration estimation models in semi-arid conditions

The best and worst performing models in the original equations were Mahringer (MAE = 0.70 mm day^-1, MAPE = 15.86%, RMSE = 0.87 mm day^-1, NSE = 0.81, R² = 0.94) and Penman (MAE = 1.84 mm day^-1, MAPE = 33.68%, RMSE = 2.39 mm day^-1, NSE = -0.49, R² = 0.91), respectively, whereas in the modified equations Dalton (MAE = 0.29 mm day^-1, MAPE = 7.51%, RMSE = 0.33 mm day^-1, NSE = 0.97, R² = 0.97) and WMO (MAE = 0.36 mm day^-1, MAPE = 8.89%, RMSE = 0.43 mm day^-1, NSE = 0.95, R² = 0.97). The RMSE errors of the daily average ET_o values estimated using the modified equations were generally below the acceptable error limit (RMSE < 0.50 mm day^-1). It has been concluded that the modified equations of the six mass transfer-based models can be used as alternatives to the FAO-56 PM equation under the Van Lake microclimate conditions (NSE > 0.75), while the original equations-except for those of Mahringer (NSE = 0.81), WMO (NSE = 0.79), and Romanenko (NSE = 0.76)-cannot be used.