Weather forecast: will violent thunderstorms increase over the next few years?

After a week of strong thunderstorms and heavy rains, several cities such as Reims and Beauvais were flooded causing one death and extensive material damage.

In less than an hour, the cities of Reims, Beauvais, Houille, Lyon found themselves under water, leaving only the top of buried cars and shops transformed into footbaths. Monday, June 21, while France was celebrating the Fête de la Musique, a violent storm fell over the city center of Reims, letting 50 millimeters of water escape in less than two hours. Quickly uncontrollable, water infiltrated in every corner as evidenced by the various videos taken by the inhabitants. Two days earlier, the capital of Champagne had already been almost completely submerged.

During the same night, a few kilometers further south, the city of Beauvais suffered the same fate. Shops strewn with mud, impassable roads, the storm of a “an exceptional scale», According to Franck Pia, first deputy mayor of Beauvais, surprised the whole population. Torrential rains that even cost the life of a young man who suddenly fell into the Thérain river, out of his bed. Despite the intervention of 18 divers, drones with thermal cameras and cynotechnical teams, Eliott, who had just passed his high school exam, was found dead “about fifty meters from the drop point“, Informed Wednesday June 23 the prosecutor of Beauvais, Carole Tharot.

After having affected all regions, these situations “apocalyptic», To use the words of Franck Pia, are they called upon to reproduce more often as was the case in the last two weeks in Reims?

Not necessarily more recurring but more intense

More often, not necessarily, replies climatologist Françoise Vimeux, Director of Research at the Institute for Research for Development (IRD). When we look at the statistics for the last twenty years, the number of thunderstorms has not particularly increased, but their intensity has ”. A thunderstorm is created by the meeting of two air masses, one very hot and another colder, causing condensation of the water present in the form of vapor on the ground then falling in heavy rains. For the climatologist, it is precisely the quantity of water that will increase in the coming years. “With higher temperatures, the atmosphere can contain more water vapor, so the rains will be more consistent once the mercury has dropped.For example, by the end of the century, rains should increase by 20%, especially during events such as the Cévennes episodes, according to climate projections.

If the rains are expected to multiply and intensify over the next few years, how can we explain that drought episodes follow the same upward curve? “It is not contradictory, answers Françoise Vimeux. On average, we will have less cumulative rain but more major extreme events, whether they are rainy and stormy episodes or periods of heatwave.“. In addition, very often, thunderstorms are born following episodes of high heat and put an end to them. “A double penalty for the soils, continues the climatologist, because sudden precipitations do not hydrate the soils, the quantity of water is too important and sudden.If these extreme climatic incidents increase, is France ready?

More concrete and less waterproof floors

Françoise Vimeux is formal, “the pipes are insufficient, they cannot absorb the quantity of water and must be adapted“. It calls for an adaptation policy not only vis-à-vis climate change but also our infrastructure. “The concreteization of soils and urban sprawl are equally responsible for the latest incidents», Notes the researcher. In fact, in cities, water does not infiltrate the soil but flows and then stagnates, thus forming masses of water. However, the situation is not improving. According to the INRA report on soil artificialization, published in 2017, “between 2006 and 2014, France lost 490,000 hectares of agricultural land, areas that absorbed rainwater“.

If today 10% of the soil is concreted, the trend is accelerating at the speed of 16,000 to 61,000 hectares per year, according to the France Strategy report of 2019. An increase against which the government has committed with “The objective of zero net artificialization”, an important chapter of the 2019 Biodiversity Plan, an observatory of soil artificialization having been launched for the same occasion. Among the lines of thought is better town planning, more responsible for the land by limiting urban sprawl as much as possible. Urgent measures must be taken, according to the first conclusions of the IPCC, which foresees the multiplication of episodes of wet heatwaves, conditions that are difficult to bear for humans.


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