Table 4.

Performance indicators used for the evaluation of SPA. Equations and units are reported.

Performance Indicator	Equation	Unit
Root Mean Square Error (RMSE)	$RMSE = \sqrt{\frac{1}{n}{\displaystyle \sum _{i=1}^n}({\widehat{y}}_i-y_i{)}^2}$	days
Mean Bias Error (MBE)	$MBE=\frac{{\displaystyle {\sum }_{i=1}^n({\widehat{y}}_i-y_i})}{n}$	days
Relative RMSE (RRMSE)	$RRMSE=RMSE/\overline{y}$	unitless
Efficiency (EF)	$\left[EF=1-\frac{{\displaystyle \sum {(y_i-{\widehat{y}}_i)}^2}}{{\displaystyle \sum {(y_i-{\overline{y}}_i)}^2}}\right]\times 100$	%

Where y₁ is the observed value for the i observation, ${\widehat{y}}_i$ is the predicted value, and $\overline{y}$ the average of observations.