Weather: why are the storms so violent this summer, and why will it take some getting used to?

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It’s a real storm that has been sweeping over a large part of France since Tuesday August 16, 2022. Flooded metro corridors in Paris, river of hailstones in the Loire, waterspouts off Corsica… From North to South of countries, the scenes that accompany the weather phenomenon are almost apocalyptic.

Thursday, August 18, the storms were so violent and the gusts of wind so powerful (up to 230 km / h) on the island of Beauty that 5 people lost their lives, including a young 13-year-old girl. Several people were also injured. The Minister of the Interior, Gérald Darmanin, went there in the afternoon.

And the island, placed in orange vigilance by Météo France shortly after 4 p.m., has not finished with the meteorological chaos. The institution thus announces in its latest bulletin a “new rainy-stormy episode over Corsica from this evening and until tomorrow morning”, with heavy rainfall, hail and strong electrical activity, even if the gusts of wind should be “less than those of this Thursday morning”.

After a succession of heat waves, also painful for the French territory, in the grip of a great drought, it would therefore seem that the weather is not giving us any respite this summer. But why?

“It is an altitude disturbance, called a thalweg, which crosses the country from the west and which, outside the winter period, is at the origin of the development of thunderstorms, which can be locally violent, on large portions of the territory” reports Philippe Arbogast, head of general forecasting at Météo France, to the newspaper Le Parisien.

At the Weather Channel, there is also talk of a “depression associated with cold air at high altitude, which circulates slowly over the PACA region and Corsica as well as in the Basque country, slowly evacuating towards Italy. This pattern results in strong diffuse instability on Thursday, following the massive and more widespread thunderstorms yesterday Wednesday.”

The phenomenon would also be all the more violent, underlines Philippe Arbogast in the daily newspaper, that it would be “confronted and supplied with humidity and heat by an exceptionally hot, humid and unstable air mass coming up from the Mediterranean”.

Above all, the storms that hit France this week were accompanied by particularly impressive phenomena, because they are quite rare: torrential downpours of rain, torrents of hail, the formation of waterspouts…

And these sporadic disruptions are not insignificant: they are rather directly linked to the record drought that is hitting the country.

“The various heat waves have made the soil extremely dry this summer. The earth gradually settled and became more and more impermeable until it was not soaked by the rain”, analyzes Nolwenn Lesparre, geophysicist specializing in hydrology at the University of Strasbourg and researcher at the CNRS, still in the columns of the Parisian.

And the rain has also been increasing in intensity lately for a good reason: because of the rise in temperatures.

“The IPCC recently showed that one more degree in the atmosphere means 9% more water vapor in the atmosphere. More water vapor, logically, also means more rain “, explained for his part the agroclimatologist Serge Zaka to franceinfo.

This is no longer a scoop: global warming is on the way, we can expect, according to forecasters, increasingly hot summers… And therefore, increasingly violent storms.

Good news, however: the stormy episodes have allowed the drought to recede in certain regions. “Between August 14 and 18, most of the rain deficit since the end of spring has just been erased in Languedoc and Provence”, notes the Weather Channel.

According to the latest forecasts from Météo France, the storms should however stop by Friday morning, and the weekend promises to be relatively “calm” throughout France… But respite, once again , should be short-lived: a new heat wave is already announced for next week.