Statistical criterion Equations Values Classification of Performance References NSE $1-\frac{{\sum }^{\text{​}}{\left({Q}_{obs}-{Q}_{sim}\right)}^{2}}{{\sum }^{\text{​}}{\left({Q}_{obs}-{\overline{Q}}_{obs}\right)}^{2}}$ 0.75 < NSE ≤ 1.00 0.65 < NSE ≤ 0.75 0.50 < NSE ≤ 0.65 0.4 < NSE ≤ 0.50 NSE ≤ 0.4 0.4 ≤ NSE ≤ 0.70 Very good Good Satisfactory Acceptable Unsatisfactory Acceptable [53] R2 $\frac{{\sum }^{\text{​}}{\left(\left({Q}_{obs}-{\overline{Q}}_{obs}\right)\left({Q}_{sim}-{\overline{Q}}_{sim}\right)\right)}^{2}}{{\sum }^{\text{​}}{\left({Q}_{obs}-{\overline{Q}}_{obs}\right)}^{2}\ast {\sum }^{\text{​}}{\left({Q}_{sim}-{\overline{Q}}_{sim}\right)}^{2}}$ R2>0.5 R2 values > 0.5 are regarded as acceptable for model simulation [54] PBIAS $\frac{{\sum }^{\text{​}}\left({Q}_{obs}-{Q}_{sim}\right)\ast 100}{{\sum }^{\text{​}}\left({Q}_{obs}\right)}$ PBIAS < ±10 ±10 ≤ PBIAS < ±15 ±15 ≤ PBIAS < ±25 PBIAS ≥ ±25 Very good Good Satisfactory Unsatisfactory [55] RMSE $\sqrt{\frac{{\sum }^{\text{​}}\left({Q}_{obs}-{Q}_{sim}\right)}{n}}$ Value below half the standard deviation Satisfactory [56] RSR $\sqrt{\frac{{\sum }^{\text{​}}{\left({Q}_{obs}-{Q}_{sim}\right)}^{2}}{{\sum }^{\text{​}}{\left({Q}_{obs}-{\overline{Q}}_{obs}\right)}^{2}}}$ 0.00 ≤ RSR ≤ 0.50 0.50 < RSR ≤ 0.60 0.60 < RSR ≤ 0.70 RSR > 0.70 Very good Good Satisfactory Unsatisfactory [57]