Terranova et al. (2014) Rainstorms able to induce flash floods in a Mediterranean-climate region (Calabria, southern Italy)

Identification

• Journal: Natural hazards and earth system sciences
• Year: 2014
• Date: 2014-09-10
• Authors: O. Terranova, Stefano Luigi Gariano
• DOI: 10.5194/nhess-14-2423-2014

Research Groups

• Italian National Research Council, Research Institute for Geo-hydrological Protection (CNR-IRPI), Rende (CS), Italy
• Department of Physics and Geology, University of Perugia, Perugia, Italy

Short Summary

This study statistically analyzes heavy rainstorms in Calabria, southern Italy, to improve understanding of their temporal structure and spatial distribution in a Mediterranean context. It proposes a method based on rainfall thresholds to identify and characterize rainstorms capable of inducing flash floods, classifying 25 such events over a 20-year period.

Objective

• To develop and validate a method for selecting and characterizing heavy rainstorms capable of inducing flash floods in Mediterranean-climate regions, by statistically analyzing their temporal structure and spatial distribution in Calabria, southern Italy.

Study Configuration

• Spatial Scale: Calabria, southern Italy, covering an area of approximately 15 080 km². The study focuses on small basins, typically below a few hundred square kilometers, and uses Thiessen polygons to define areas affected by rainstorms.
• Temporal Scale: The study period spans 20 years, from 1989 to 2008. Rainfall data were collected with a high temporal resolution of 5 minutes. Rainstorm events were defined as rainy periods separated by at least 6 hours of dry weather, with event durations ranging from 10 minutes to approximately 10 days, though heavy rainstorm events (HREs) were primarily considered for durations less than or equal to 24 hours.

Methodology and Data

• Models used: The study primarily employs statistical analysis and a heuristic method for event selection and characterization. Standardized Rainfall Profiles (SRPs) and a Binary Shape Code (BSC) are used to describe the temporal structure of rainstorms. Thiessen polygons are used for spatial analysis to determine the area affected by each event. The results are intended to benefit rainfall-runoff watershed models.
• Data sources: High-temporal-resolution (5 minutes) rainfall observations from 155 rain gauges distributed across Calabria (approximately one rain gauge per 100 km²). The dataset includes over 152,000 rainstorms recorded between 1989 and 2008.

Main Results

• A heuristic method was proposed to identify heavy rainstorm events (HREs) based on three simultaneous thresholds: cumulative rainfall (PEV) greater than 100 mm, maximum intensity in 30 minutes (I30) greater than 50 mm h⁻¹, and kinetic energy (EJ) greater than 29 MJ ha⁻¹.
• Applying this method, 25 distinct HREs were identified in Calabria between 1989 and 2008, comprising 17 widespread HREs (affecting areas greater than 500 km²) and 8 localized HREs (affecting areas less than or equal to 500 km²).
• Several well-known catastrophic geo-hydrological events in Calabria (e.g., the 1996 Esaro of Crotone flash flood, the 2000 Soverato flash flood, and the 2006 Vibo Valentia flash flood) were successfully identified by the proposed method, validating its effectiveness.
• Localized HREs generally exhibited temporal structures with a peak at the beginning of the event (thunderstorm-type, BSC = 1111).
• Widespread HREs often displayed mixed temporal structures, with peaks localized in the second half of Huff's curves (BSC from 0000 to 0100), sometimes resembling tropical-like cyclones (medicanes).
• The study found that damage from flash floods is not solely correlated with the spatial extent of the rainstorm, as environmental (e.g., orography) and anthropogenic (e.g., urbanization) factors also play a significant role.

Contributions

• Proposes an automatic and reproducible heuristic method for selecting and characterizing rainstorms capable of inducing flash floods in Mediterranean-climate regions, which is validated against historical catastrophic events.
• Provides a detailed statistical characterization of the temporal structure (using Standardized Rainfall Profiles and Binary Shape Codes) and spatial distribution of intense rainfall events at a sub-hourly scale for Calabria, a region representative of Mediterranean climatic and morphological conditions.
• Enhances the identification of "design storms" with realistic time structures and integrated spatial analysis, offering valuable input for rainfall-runoff watershed models and improving flood forecasting capabilities.
• Highlights the high frequency (25 heavy rainstorms in 20 years) and significant socio-economic impact of flash flood-inducing rainstorms in Calabria, contributing to risk perception and mitigation strategies.

Funding

The Calabrian Regional Agency for Environmental Protection (ARPACAL) provided access to rainfall data. No specific funding projects or reference codes were explicitly stated in the paper.

Citation

@article{Terranova2014Rainstorms,
  author = {Terranova, O. and Gariano, Stefano Luigi},
  title = {Rainstorms able to induce flash floods in a Mediterranean-climate region (Calabria, southern Italy)},
  journal = {Natural hazards and earth system sciences},
  year = {2014},
  doi = {10.5194/nhess-14-2423-2014},
  url = {https://doi.org/10.5194/nhess-14-2423-2014}
}