Amengual (2025) Characterization of extreme flash floods in Mediterranean Spain

Identification

• Journal: Journal of Hydrology
• Year: 2025
• Date: 2025-04-06
• Authors: A. Amengual
• DOI: 10.1016/j.jhydrol.2025.133229

Research Groups

• Grup de Meteorologia, Departament de Física, Universitat de les Illes Balears, Palma, Mallorca, Spain

Short Summary

This study characterizes extreme flash floods in Mediterranean Spain by collating and analyzing a comprehensive database of 99 events (1905-2023) and high-resolution data from 13 major events. It reveals that flash flood patterns mirror extreme precipitation, semi-arid basins experience higher magnitudes but steeper envelope curve decline, and event runoff coefficients are lower than in other European regions due to soil storage capacity.

Objective

• To characterize extreme flash floods in Mediterranean Spain during the extended warm season by collating and analyzing a comprehensive database of events.

Study Configuration

• Spatial Scale: Mediterranean Spain (95675 km²), focusing on catchments up to 3000 km², with detailed analysis on sub-basins as small as 1 km².
• Temporal Scale: 1905–2023 (119 years) for the main database, with detailed analysis on events since mid-2000s. Focus on the extended warm season (May-November), with event durations up to 48 hours and lag times up to 6 hours.

Methodology and Data

• Models used: Kinematic Local Excess Model (KLEM) for hydrological simulations.
• Data sources:
  • Discharge and rainfall records from regional and state institutions.
  • Scientific papers, technical reports, local flood risk mapping studies, and post-event field campaigns.
  • Digital terrain models (25 m to 50 m spatial resolution).
  • Quantitative Precipitation Estimates (QPEs) from AEMET weather radar network and automatic rain gauges (1000 m spatial resolution, 10 min temporal frequency).
  • Automatic stream gauge data (10 min intervals).
  • AEMET daily pluviometer network (records up to 2023).
  • AEMET automatic rain gauge network (10 min intervals, 2000-2019 period).
  • Budyko curve for climatic analysis.
  • Quantile regression for envelope curve derivation.

Main Results

• The spatial and temporal distributions of extreme daily precipitation and flash flooding closely match across Mediterranean Spain.
• Two flash flood severity hotspots were identified: central València to northern Alacant (Mediterranean climate) and southern Murcia to northern Almería (semi-arid climate).
• Flash floods most frequently occur in October, coinciding with the peak of absolute maximum daily precipitation.
• Envelope curves for Mediterranean climate are qp = 85 A^-0.4 and for semi-arid climate are qp = 128 A^-0.5, where qp is unit peak discharge in m³s⁻¹km⁻² and A is catchment area in km². Semi-arid basins exhibit higher flood magnitudes but a faster decline in the envelope curve with increasing drainage area.
• Total rainfall amounts for flash flood events ranged from approximately 40 mm in 4 hours to over 300 mm in less than 9 hours. Up to 60% of total rainfall occurred at torrential rates (≥20 mmh⁻¹) in drainage areas smaller than 25 km².
• Event runoff coefficients are generally low (mean 0.17 for Mediterranean, 0.14 for semi-arid) and lower than those reported in other European regions, attributed to high soil storage capacities.
• Lag times for basins smaller than 350 km² are generally above the lower bound of the European envelope curve, while for basins larger than 800 km², they fall below it, influenced by flow hydraulics.
• Flooding rise times can be less than 30 minutes. Flashiness, defined as the maximum time derivative of streamflow, shows a strong negative correlation with the logarithm of drainage size, with headwater catchments exhibiting the highest values.

Contributions

• Provides an extensive characterization of flash floods in Mediterranean Spain, complementing existing European and US databases.
• Assembles a comprehensive and high-resolution database of extreme flash floods using standardized methods, ensuring consistency for comparisons and future research.
• Integrates the high-resolution dataset into the EuroMedeFF database, expanding the collection of rainfall and flood discharge extremes across European climatic regions.
• Offers valuable insights for improving flash flood risk management, supporting civil protection, and advancing hydrometeorological forecasting systems in Mediterranean Spain.

Funding

• TRAMPAS (PID2020-113036RB-I00)
• HYDROMED (PID2023-146625OB-I00)
• Funded by MICIU/AEI/ 10.13039/501100011033 by ERDF/EU

Citation

@article{Amengual2025Characterization,
  author = {Amengual, A.},
  title = {Characterization of extreme flash floods in Mediterranean Spain},
  journal = {Journal of Hydrology},
  year = {2025},
  doi = {10.1016/j.jhydrol.2025.133229},
  url = {https://doi.org/10.1016/j.jhydrol.2025.133229}
}