The Nash-Sutcliffe model efficiency coefficient (E) is commonly used to assess the predictive power of hydrological discharge models. However, it can also be used to quantitatively describe the accuracy of model outputs for other things than discharge such as nutrient loadings, temperature, concentrations etc. The question for E is shown below. Nash-Sutcliffe efficiencies can range from -infinity to 1.0. An efficiency of 1.0 corresponds to a perfect match between model and observed data, whereas an efficiency less than 0.0 occurs when the observed mean is a better predictor than the model.
Note - this model assumes the observed data is regularly spaced in time. If the spacing of observation times is not constant, please consider one of the following models: