Characterization of Extreme Rainfall Events Severity in Calabria: Exploring Spatial-Temporal Variability through Severity Diagrams

This study aims to identify key characteristics of rainfall events, such as critical duration, extent, and severity (i.e., return period), to unveil potential dependencies with the resulting impact scenarios. Severity diagrams, introduced by Ramos et al. (2005) serve here as a straightforward tool, providing a synthetic visualization of storm severity while accounting for the complexity associated with rainfall spatial variability and duration. The method emphasizes the coexistence of extreme and ordinary (non-extreme) rainfall intensities. In contrast, the conventional approach of assigning a single return period to an event obscures a significant portion of storm complexity by overlooking spatial variability. Maximum mean areal precipitations observed over different areas during the storm event are evaluated. Subsequently, maximum equivalent point rainfalls are derived using ARF (Areal Reduction Factor) estimation, and their return period values deduced from the IDF (Intensity Duration Frequency) curves. The return periods are eventually mapped as a function of area and duration of rainfall accumulation. Several damaging storm events observed in the Calabria region (south Italy) over the last 20 years have been selected as illustrative examples for the analysis.