Flood and submersion risks in the Gulf of Lion

Introduction

The French Mediterranean coastline, and in particular the Gulf of Lion, is exposed to major climatic risks. Among these, flooding caused by Mediterranean episodes and marine submersion due to rising sea levels and storms are very real threats. This two-part feature looks at these phenomena and their impact on coastal areas, particularly campsites by the sea.

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Episode 1: Mediterranean episodes and the risk of flooding

The Aiguat and torrential flooding

Mediterranean episodes, known locally as "Aiguat" in Catalonia, are meteorological phenomena characterised by intense rainfall in a very short space of time. One of the most striking events was in 1940, when 1,100 mm of rain fell in 24 hours, a European record that still stands today. By way of comparison, the flooding of the Roya in 2020 recorded 500 mm of rainfall, and storm Gloria in the same year recorded around 318 mm.

Link to detailed analysis of the 1940 Aiguat

In January 2020, storm Gloria hit the Pyrénées-Orientales region hard. The Agly, Tech and Têt, three coastal rivers, overflowed their banks following torrential rainfall, flooding their alluvial plains.

Storm Gloria 2020

L'Indépendant video on storm Gloria

During these events, the combination of low atmospheric pressure and the force of the storm's winds caused a rise in sea level, blocking the evacuation of river water. This configuration is similar to the storm surges observed on the Atlantic coast and favours the flooding of coastal areas.

A scientific look at these phenomena

Florence Vaysse, a meteorologist at Météo France, gives a detailed explanation of the mechanisms of the Aiguat and its consequences. Her analysis is highlighted in the documentary Sometimes it rainsdirected by Arnaud Brugier. This film, co-produced by France Télévisions and Les Productions de la Main Verte, looks back at the devastating floods of 1940 and asks whether a similar event could happen in the future.

Video and report on the documentary Sometimes it rains

Access to the documentary on Vimeo

Impact on campsites and infrastructure

This torrential rainfall causes flash floods and overflows of coastal rivers. In their estuaries, the combination of rising water levels and strong winds prevents the rivers from flowing, flooding vast areas. This has a direct impact on seaside campsites, where mobile homes can be submerged in a matter of hours.

Report on flooding in Spain in 2023

Wikipedia article on the flooding in Valencia at the end of October 2024

Article in the Independent newspaper on the risk of flooding at campsites in 2024

An ever-present threat

The authorities are taking these risks into account and are undertaking adaptation work. For example, the reinforcement of dykes and the widening of the bed of the river Agly are among the measures put in place despite the persistent drought in the Pyrénées-Orientales.

Article on the work to rebuild the Agly dykes

Find out more in the following post 

Episode 2: Marine submersions and coastline erosion in the Gulf of Lion
100% is the probability of marine submersion in the Mediterranean over the next 35 years.