Nash-Sutcliffe Statistic

Validating hydrologic models can be challenging depending on a magnitude of factors. Because of this, VELMA produces a variety of outputs after each simulation that can be used for analysis, one of them being the Nash-Sutcliffe coefficient. The Nash–Sutcliffe model efficiency coefficient is used in VELMA for validate the results of simulated flow based on gauge station flow data. The model was developed in 1970 specifically for river flow forecasting. The Nash-Sutcliffe equation is: whereis the mean of the observed values, SD represents the standard deviation of the observations. andrepresent the sample (of size N) containing the observations and the model estimates.The resulting values range from −∞ to 1 with an acceptable score being between 0.5 – 0.65. The Nash-Sutcliffe statistic is a normalized goodness of fit statistic where negative values normally do not occur unless there are multiple errors. This efficiency coefficient, of the many results produced by VELMA, is the output that we chose to use to analyze the results of our modeled watersheds. (Nash and Sutcliffe, Ritter and Muñoz-Carpena, hydroGOF).

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