Deviation of runoff Volume

The deviation of runoff volumes Dv, also known as the percentage bias, is perhaps the simplest goodness-fit criterion. The deviation of the runoff volumes is given by WMO (1986). For a perfect model, deviation of runoff volumes is equal to zero. The smaller the deviation of runoff volumes value, the better the performance of the model (Gupta et al., 1999). In the case of Dv, there is no need to increase the number of accuracy criteria by using different formulas for a single year or season and for an average of several years or seasons.

where O is the observation value and S is the forecast value.