Drought, marine heatwave in the Mediterranean… Why we can fear heavy flooding in the fall

11:40 a.m., August 28, 2022

A thirsty country, before a flooded country? In the wake of a first quarter where temperatures reached unprecedented levels, the summer was marked by scorching waves and unprecedented drought throughout the country. More than 60,000 hectares of forest went up in smoke. This assessment, already heavy, could have other consequences this fall. On Tuesday, Météo-France will reveal the updated version of its three-month forecast. In its previous version, the agency already anticipated higher than normal temperatures throughout the territory until October and a lasting drought in the northeast quarter. The probability that Cévennes phenomena (or Mediterranean rains) will occur appears high. While it is perilous to predict where and how precipitation will fall, the trend of recent years suggests episodes of increasing severity.

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Among the elements causing concern is the sea heat wave observed this summer in the Mediterranean – between 27 and 30 degrees at the end of July, ie 4 to 6 points above normal. These high temperatures are one of the factors that can accentuate the intensity of the Cévennes episodes, violent precipitation that occurs locally on very dry land, incapable of absorbing water. However, water reserves are below normal everywhere in France. “An atypical situation, emphasizes Violaine Bault, at the Bureau of Geological and Mining Research (BRGM), particularly worrying in Paca to the south of Drôme and from the north of New Aquitaine to Pays de la Loire. »

15 targeted departments

Usually, the heavy rains of August and September recharge the water tables a little but, in recent weeks, despite the storms, his colleagues in the south of France have hardly seen the levels rise. “What it takes, continues Violaine Bault, it is a fine and continuous rain to moisten the land and allow the vegetation to drink. »

Failing this, in the event of a sudden accumulation of precipitation, instead of playing the role of a sponge, the ground acts rather “like a slide”, summarizes Lieutenant-Colonel Éric Agrinier, spokesperson for the Gard firefighters. What cause sudden flooding. “We had a little glimpse of it a fortnight ago, with the first phase of thunderstorms in Hérault, southern Gard, then Bouches-du-Rhône and Var, continues Eric Agrinier. While that didn’t cause major damage, two hours of rain was enough to cause runoff in the streets. »

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Depending on the location of these bad weather, autumn floods can cause significant damage, material and human: 15 deaths in the Aude in 2018, 20 in the Alpes-Maritimes in 2015. Faced with this risk, the Minister for Ecological Transition , Christophe Béchu, launched a prevention campaign on Tuesday targeting the inhabitants of 15 departments around the Mediterranean (Alpes-de-Haute-Provence, Alpes-Maritimes, Ardèche, Aveyron, Aude, Bouches-du-Rhône, Corse-du-Sud , Haute-Corse, Drôme, Gard, Hérault, Lozère, Pyrénées-Orientales, Var and Vaucluse). With common sense advice, such as postponing your trips, leaving your children at school, staying inside buildings and going upstairs… ” Attention, insists Lieutenant-Colonel Agrinier, even in the event of a yellow alert, you must remain vigilant because it can quickly switch to orange and red. »

Drought, marine heatwave in the Mediterranean… Why we can fear heavy flooding in the fall