Severe bad weather is underway in the south of France.
They took shape on Monday and continue until Wednesday morning.
This Tuesday, it is in Hérault that they are most marked with intense rains and winds reaching around 100 km/h on the coasts.
The phenomenon can be described as a “Cévennes” episode.
This name is explained by the location of bad weather.
They are located in the Cévennes mountain range, to the south-east of the Massif Central.
The qualification also holds when precipitation occurs near this area, which is the case for Hérault.
Up to a month of rain in 36 hours
But the Cévennes episode is in fact only a local variation of a more general meteorological phenomenon called the “Mediterranean episode”.
Its characteristics are twofold.
From a geographical point of view it takes place on the shores of the Mediterranean Sea and in the regions bordering it.
Meteorologically, this is a sudden massive accumulation.
The mountainous terrain of the Cévennes and the foothills of the Alps which border part of the Mediterranean contribute to the fact that precipitation sometimes stagnates, making it all the more dangerous.
Generally, Mediterranean episodes occur at the end of summer and beginning of autumn, when the sea air is both warm and humid.
But they can take place all year round.
The region is also experiencing a fairly exceptional succession with a fifth occurrence since February.
Concerning the current episode, accumulations of around 120 mm are expected.
This level could locally be exceeded and reach 150 mm, that is to say 150 liters per square meter in 36 hours.
This corresponds to about a month of precipitation in the region.
💦💦The episode of heavy #rain expected between Monday evening and Wednesday morning will mainly be in the Cévennes with accumulations of up to 120 millimeters, the equivalent of 3 weeks of precipitation.
#Floods are expected on the rivers descending from the Cévennes.
pic.twitter.com/jks8d0Qupk
— La Chaîne Météo (@lachainemeteo) March 25, 2024
However, these accumulations are far from records.
In 2020 for example, in Valleraugue, in Gard, 500 mm fell in just 12 hours (500 liters per square meter), as Météo France recalls.
The most common case is an accumulation of around 100 mm (100 liters per square meter), like the current episode, but reached in just an hour or two, which causes damage and threatens lives.