A methodology to perform a regional frequency analysis centred on a target site is proposed. The spatial extremogram technique is used to form a physically and statistically homogeneous region around the site of interest. This is of fundamental importance to conducting a more proper regional analysis. A regional frequency estimation of extreme skew storm surges on the French coasts is carried out.

The use of historical data in a regional analysis can reduce the uncertainties in extreme quantile's estimation. Historical data are significant extreme events that are not recorded by tide gauge. They usually look like isolated data and they are different from continuous data from systematic measurements of tide gauges. Thanks to the use of the credible duration concept, the proposed FAB method allows the use of historical data together with systematic data in a regional framework.