Methodologies for the characterisation of spatially distributed hydrological events: the Italian case study.

Evaluating historical extreme flood events is fundamental due to their socioeconomic impacts. In this context, the spatial distribution of the event has a key role and the univariate approach, based on the analysis of local flood frequency on a single site, is not the proper one.

For this reason, in the recent past, an increasing amount of research has focused on the regional characterization of flood events, trying to describe their temporal and spatial distribution. The main objective of this work is the comparison of two different methods widely used for the selection and characterization of spatially distributed flood events for risk assessment purposes. Both methods were applied to the Italian territory and compared in terms of parameters used, results obtained, and technical analogies and differences. 

The two methodologies reveal similar results, comparable with a list of extreme events produced as a collection of historical flood reports. The results show that floods co-occurring in several basins are unevenly distributed, with a higher number of selected events occurred in Northern and Central Italy, where the largest Italian basins are located.