Biondi et al. (2025) Storm severity assessment: Application of severity diagrams to events in Calabria (southern, Italy)

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2025
• Date: 2025-12-01
• Authors: Daniela Biondi, Sara Bloise, Angela Corina
• DOI: 10.1016/j.ejrh.2025.103000

Research Groups

• Department of Computer Engineering, Modelling, Electronics and Systems, University of Calabria, Rende (CS), Italy
• Italian Civil Protection Department, Roma, Italy

Short Summary

This study applies and adapts severity diagrams to assess and visualize storm severity in Calabria, southern Italy, by explicitly incorporating areal extent, duration, and intensity into return period estimation. The research demonstrates that severity diagrams effectively capture the complexity of rainfall events, providing a synthetic visualization and enabling systematic classification for enhanced flood risk analysis and civil protection.

Objective

• To apply and adapt severity diagrams for assessing and visualizing storm severity in Calabria, southern Italy, explicitly incorporating areal extent, duration, and intensity in return period estimation.
• To combine severity diagrams with regional statistical techniques to address the characteristics of the Calabria monitoring network.
• To present a methodology based on severity diagrams to classify and characterize the most intense rainfall in terms of severity, spatial extent, and duration for operational relevance in flood risk management.

Study Configuration

• Spatial Scale: Calabria region, southern Italy (approximately 15,000 km²), with analyses conducted at the scale of eight national civil protection alert zones (average 1850 km² each). Moving areas from 1 km² to 625 km² were investigated.
• Temporal Scale: Rainfall data from 2002 to 2015. Event durations investigated ranged from 1 hour to over 50 hours, with 1-hour intervals for events up to 24 hours and 3-hour intervals for events exceeding 24 hours.

Methodology and Data

• Models used:
  • Severity diagrams (based on Ramos et al., 2005, and Ceresetti et al., 2012)
  • Regional statistical techniques: Index-flood method (Dalrymple, 1960)
  • Two-Component Extreme Value (TCEV) distribution (Rossi et al., 1984)
  • Inverse Distance Weighting (IDW) for spatial interpolation (Shepard, 1968)
  • Areal Reduction Factor (ARF) formulation by Eagleson (1972)
• Data sources:
  • 20-minute rain gauge data series from 154 rain gauges in the Calabria region, obtained from the Regional Multi-Risk Center (http://www.cfd.calabria.it/).
  • Rainfall data from 2002 to 2015.
  • A database of events with observed ground impacts, cross-referenced with previous studies (Greco et al., 2020; Biondi et al., 2021).

Main Results

• Severity diagrams effectively capture the coexistence of multiple rainfall characteristics (intensity, duration, spatial extent), providing a synthetic visualization of storm complexity and identifying critical scales.
• The method successfully represents diverse storm dynamics, from highly localized convective events (e.g., July 3, 2006) to widespread, prolonged systems (e.g., October 30 – November 2, 2015).
• A systematic classification of storm events based on severity, duration, and areal extent was developed, enhancing operational relevance for flood risk analysis and civil protection.
• Events with high severity (return periods T > 100 years) are predominantly characterized by highly concentrated, intense rainfall affecting relatively small areas (<100 km²) and short durations (<6 hours).
• Moderate severity events (10 < T < 100 years) also primarily impact small areas and short durations but can extend to longer durations.
• Low severity events (T < 10 years) can occasionally affect broader areas (>500 km²) and are often associated with significant antecedent rainfall, influencing ground impacts.
• The study confirms the adaptability of severity diagrams in a morphologically complex region with a less dense monitoring network, supported by a robust regional statistical framework.

Contributions

• First application of severity diagrams in the considerably larger and morphologically complex Calabria region (southern Italy), expanding beyond previous, smaller-scale studies.
• Analysis of a broader and more diverse set of storm events (2002-2015), including multi-day rainfall and catastrophic events with documented ground effects.
• Methodological adaptation incorporating regional statistical techniques (VAPI project's hierarchical regionalization procedure, index-flood method, TCEV distribution) to overcome data limitations and enhance the robustness of severity assessments in data-scarce environments.
• Introduction of novel criteria for characterizing critical rainfall events from severity diagrams, focusing on intensity, spatial extent, and duration, which improves the understanding of rainfall combinations most likely to cause severe impacts.
• Enhances the operational relevance of severity diagrams for civil protection by supporting event cataloguing, early-warning validation, and the refinement of rainfall thresholds in complex scenarios.

Funding

• Cooperation agreement between Italian National Civil Protection and Camilab DIMES Unical, Accordo Biennale 2022–2024 ‘Criteri di allertamento, valutazione delle conseguenze e preannuncio di eventi idrogeologici estremi relativi al rischio da frana e da inondazione’.

Citation

@article{Biondi2025Storm,
  author = {Biondi, Daniela and Bloise, Sara and Corina, Angela},
  title = {Storm severity assessment: Application of severity diagrams to events in Calabria (southern, Italy)},
  journal = {Journal of Hydrology Regional Studies},
  year = {2025},
  doi = {10.1016/j.ejrh.2025.103000},
  url = {https://doi.org/10.1016/j.ejrh.2025.103000}
}