Storm severity assessment: Application of severity diagrams to events in Calabria (southern, Italy)

This study focuses on Calabria, southern Italy, located in the central Mediterranean, a region prone to hydrogeological hazards due to complex morphology and intense precipitation events. This study applies a straightforward approach for assessing and visualizing storm severity that explicitly incorporates key storm characteristics, such as areal extent, duration, and intensity, in return period estimation. The work combines the application of severity diagrams to a new case study, involving a larger set of storm events compared to previous studies, with a methodological component based on regional statistical techniques, necessary due to the characteristics of the Calabria monitoring network. In addition, a methodology based on severity diagrams to classify and characterize the most intense rainfall in terms of severity, spatial extent, and duration is presented. This study illustrates how severity diagrams capture the coexistence of multiple rainfall characteristics, providing a synthetic visualization of storm complexity. Two case studies with markedly different spatial and temporal patterns highlight the effectiveness of the method in representing diverse storm dynamics, from widespread systems to highly localized events. In addition to their descriptive value, severity diagrams also prove capable of enabling a systematic classification of storm events, derived from a broader dataset and based on key features. This classification enhances their operational relevance for flood risk analysis and civil protection, supporting event cataloguing, early-warning validation, and the refinement of rainfall thresholds in complex scenarios. • Severity diagrams effectively identify key characteristics of storm events • Severity diagrams are applied to Calabria storms using regional statistics • They support storm classification based on severity across space and duration