On the use of a four-parameter kappa distribution in regional frequency analysis

New developments are presented enabling the using a four-parameter kappa distribution with the widely used regional goodness-of-fit methods as part of an index flood regional frequency analysis based on the method of L-moments. The framework was successfully applied to 564 pooling groups and was found to significantly improve the probabilistic description of British flood flow compared to existing procedures. Based on results from an extensive data analysis it is argued that the successful application of the kappa distribution renders the use of the traditional three-parameter distributions such as the Generalised Extreme Value (GEV) and Generalised Logistic (GLO) distributions obsolete, except for large and relatively dry catchments. The importance of these findings are discussed in terms of the sensitivity of design floods to distribution choice.