Study of major flood events in Spain over the last 750 years

The AMARNA Platform contains a catalogue of 12,000 episodes of adverse meteorological conditions in Spain, covering the last 1,000 years. This enables studies to be carried out on flood events, covering not only current episodes but also those of greater severity and lower frequency that have occurred in climatic and historical contexts different from the present day.

            This study aims to assess the most severe flood episodes to have occurred in Spain over the last 750 years (1275-2025). For this purpose, the available records identify up to 5,438 episodes in which some type of flood occurred, whether caused by rain, rivers or tides. An initial selection of episodes focused on those that resulted in at least one case of river overflow leading to the complete destruction of a building or infrastructure (including houses, bridges, water mills, dams or canals) and that led to evacuations, rescues, injuries or fatalities. This resulted in 271 episodes.

            For these events, composite indices are derived by weighting the values of certain numerical variables: the structural impact index, the human impact index, the number of affected river basins, and the density of overflow records comprising the event. A list of 53 major events is compiled, to which two different weighting schemes are applied: one emphasising the structural impact component and the other the human impact.

            The results provide a continuous historical overview of the severity of the various episodes, highlighting that those with the greatest structural impact occur during climatic fluctuations already recognised during the Little Ice Age for their high frequency of such phenomena. Whereas since the second half of the 20th Century, the severe episodes that have occurred, including the late October 2024 Valencia area episode, have had a greater impact on people than on buildings and infrastructures. This well-documented divergence may contribute to our understanding of mechanisms for the prevention and management of such emergencies. However, it also highlights that, on a historical scale, episodes with significant destructive potential have occurred and could recur in the current context, with a substantially increased population and similarly high levels of vulnerability.

Acknowledgements:

The authors acknowledge the grants from FLOODMED (PID2024-157662OB-C22), funded by the Spanish Ministry of Science, Innovation and Universities (MICIU/AEI/10.13039/501100011033) and by ERDF/EU.