Performance evaluation of calibrated radiation-based ET0 equations against standard FAO56-PM model in humid climatic condition

Abstract

In this study conducted with specific objective to evaluate performance of original and calibrated versions of different radiation-based ET0 equations in comparison to standard FAO56-PM model for humid Dehradun district of Uttarakhand (India), it was found that all calibrated ET0 equations performed much better in comparison to their original versions. The calibration coefficients were found to decrease in the range of 5.37% (Val 1) to 42.62% (M-B) while it was increased in between 4.83% (S-S) and 82.57% (F24-Rad). All equations (except Val 1, Han, C-R and dB-S) after calibration showed significant increment in value of agreement index (D) in between 0.58% (MP-T) and 64.43% (M-B). With calibrated versions of Val 1, Han, C-R and dB-S equations, value of D was decreased to the tune of 0.95%, 2.76%, 3.40% and 3.48%, respectively and yielded increased RMSE values as 26.72% (Val 1), 20.60% (Han), 42.22% (C-R), and 40.13% (dB-S), while calibrated versions of remaining 16 equations showed significant decrement in RMSE values in between 26.39% (MP-T) and 85.79% (B-G). The values of MAXE, MBE, PE and SEE for calibrated equations decreased in the range from 15.05% (Val 1) to 593.77% (F24-R); 41.28% (X-S) to 429.47% (dB-S); 13.52% (Han) to 97.02% (B-G), and 5.25% (Val 1) to 42.63% (M-B), respectively, whereas after calibration, values of these statistical indices increased in the range of 75.00% (Val 1) to 373.33% (Tan); 299.17% (Val 1); 59.27% (Han) to 299.17% (Val 1), and 4.73% (S-S) to 82.83% (F24-Rad). The calibrated B-G, MP-T, P-T, and Val 2 equations yielded best R values as 0.99 with decrement in their original coefficients of 34.24%, 8.05%, 13.90% and 17.52%, respectively, while worst results in terms of higher R value were found with calibrated Bert (1.13) and X-S (0.60) equations.