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.