Uncertainty assessment of regionalized flood frequency estimates

A simplified approach is presented to uncertainty assessment of regionalized flood frequency estimation by the generalized extreme value distribution. First, an approximate formulation of the variance of quantile estimators is introduced to evaluate the confidence limits of the estimated growth curve of regionalized flood flows. Then this result is combined with the variance of index flood estimators to obtain an uncertainty model for evaluating the variance of flood estimators by the index flood method. This approach is finally used to introduce an efficiency index to discriminate between single-site analysis and the index flood method. Examples of application to northwestern Italy are reported and discussed.