Investigation of 16 calibrated Valiantzas' evapotranspiration equations against standard FAO56-PM model in Indian humid climatic condition

Abstract

The study was conducted with an objective to evaluate the performance of calibrated versions of different Valiantzas evapotranspiration (ET) equations over their original counterparts for humid climatic conditions prevailing at Dehradun district of Uttarakhand in comparison to standard FAO56-PM model as an index. The calibration coefficients were found to decrease in the range from 3.23% (Val 7) to 40.87% (Val 15). All calibrated Valiantzas equations (except Val 2, Val 7 and Val 13) showed significant increment in agreement index (D) between 0.01% (Val 5) and 34.84% (Val 15). With calibrated versions of Val 2, Val 7 and Val 13 equations, value of D was found to decrease to the tune of less than 1% with increased RMSE values, while calibrated versions of remaining 13 Valiantzas equations showed significant decrement in RMSE values. The calibrated versions of all Valiantzas equations showed reduction in MAXE values in between 14.29% (Val 7) to 84.55% (Val 15). Except Val 7 equation, the values of MBE and PE for calibrated Valiantzas equations decreased in the range from 87.22% (Val 16) to 196.49% (Val 6) and 3.49% (Val 6) and 93.32% (Val 15), respectively while SEE values with calibrated equations decreased in the range from 2.77% (Val 6) to 40.87% (Val 15). Almost all calibrated Valiantzas equations extended best R-values (near to 1.00) and they performed much better in comparison to their original versions.