The south of France has once again been affected in recent days by a Mediterranean episode.
These rainy weather events, which dump large quantities of water over a small area, have caused the death and disappearance of several people.
Beyond the human toll, this tragedy raises a certain number of meteorological questions.
Le Parisien comes back to this in three stages.
Are the quantities of water that fell exceptional?
The area concerned cuts across Lozère, Ardèche, Var and the Alpes-Maritimes.
“In the Cévennes, between 100 mm and 150 mm fell between Saturday morning and Sunday morning,” according to Météo France.
This corresponds to a quantity of up to 150 liters per square meter.
In the Var, accumulations have often exceeded 100 mm, or 100 liters per square meter.
At height, in the Ardèche Cévennes, it could even fall to more than 300 mm, therefore more than 300 liters per square meter in 48 hours.
Added to this violence characteristic of Mediterranean episodes is their repetition, which makes floods even more dangerous.
This was the third phenomenon of its kind in three weeks.
The soils were already full of water and runoff was facilitated by the first two waves of bad weather.
Despite this, the accumulations are “not exceptional compared to the Mediterranean episodes usually encountered in autumn or winter”, explains Météo France.
Is such a phenomenon common in March?
This is where the specificity lies.
The precipitation totals are certainly not out of the norm for the region.
But they “are unusual for the month of March”, specifies the meteorological organization.
Mediterranean episodes are generally concentrated in the fall.
Météo-villes points out, for its part, that 80% takes place in the months of September, October, November and December alone.
By expanding to the months of August and January which are on the edge of this period, 90% is reached.
The months of March to July concentrate between 1% and 2% of this type of phenomenon.
It is therefore something rare at this time, even more so with such repetition as in recent weeks.
But in March 2022, more than 400 mm (400 liters per square meter) fell, for example, on the Hérault Cévennes.
The Météo France archives also mention, in the Var, a total of 110 mm (110 liters per square meter), in Saint-Raphaël, on March 26, 1999. On March 13, 1980, a total of 110 mm (110 liters per meter square) was recorded in Sospel, in the Alpes-Maritimes.
Can a link be made with global warming?
Faced with such phenomena, the question of a link with climate change comes up regularly.
The answer is not obvious and requires careful consideration.
Global warming can at least partly be mentioned.
Météo France thus recalls that “scientific studies agree to conclude that there is an increase in the intensity of these Mediterranean events in a warmer climate”.
Two objective elements should be noted over the period covering the decades corresponding to global warming.
Between 1961 and 2022, heavy precipitation has intensified: daily rainfall totals, measured over a year, have increased by 12%.
Furthermore, the most violent Mediterranean episodes have doubled in frequency over the same period.