Deviation of Gain
In contrast to R2, there are no significant problems in computing the average DG for periods comprising several years. The coefficient of gain from the daily mean, DG, compares model results with daily mean discharge values, which vary throughout the year. DG can vary between 0 and 1, with 0 being a perfect model (WMO, 1986).
where O is the observation value and P is the forecast value and Obar is the average measured daily discharge.
Paste 2-columns data here (obs vs. sim). In format of excel, text, etc. Separate it with space: