• Storms are expected in France from this Tuesday, after a long period of heat wave.

  • The arrival of intense rain has brought relative respite to firefighters from the fires, with fires now fixed in Gironde, Drôme and Jura.

  • 20 Minutes

    looks at these stormy precipitations and their consequences, thanks to the analysis of Jean-Michel Soubeyroux, climatologist at Météo-France.

After the good weather, the rain.

France suffered a period of particularly intense heat wave but violent storms are expected from this Tuesday.

In the next few days, the weather is expected to intensify.

But are these violent rains good news?

20 Minutes

takes stock with Jean-Michel Soubeyroux, climatologist at Météo-France.

Are these precipitations welcome for the dryness of the soil?

A driving rain came this weekend to the chagrin of the Augustians.

But to the delight of our thirsty soils.

Unfortunately, "the infiltration of water could be slowed down by the dryness of the soil", explains Jean-Michel Soubeyroux, climatologist at Météo-France.

On clay soils, water infiltrates with difficulty, especially when it falls in a big whirlwind.

"The problem is more the intense rains than the dryness of the soil", underlines the climate expert who adds that if the rains were moderate, the soil could slowly moisten and absorb water.

But, this Tuesday, Météo-France warned of a stormy episode and locally, accumulations of 20 to 40 millimeters in less than an hour are expected.

However, “the water must first moisten the surface soil,” so these rapid precipitations risk causing runoff, especially in urban areas where the soils are often impermeable.

Difficult, indeed, to cross the macadam.

Even for a drop.

However, this precipitation is still good news.

“Each moment has its urgency.

We must first reduce the water stress of the vegetation”, deciphers the climatologist.

After months of drought, French plants will finally receive some water.

A welcome hydration while some trees look gray and seem to come straight from autumn.

It is also good news for the fires as in the European Union, more than 660,000 hectares have been burned since January.

A record since the start of satellite data in 2006. The arrival of rains has, in fact, brought relative respite to firefighters from the fires, with fires now fixed in Gironde, Drôme and Jura. 

Will this precipitation prepare us for winter?

Nature doesn't store water the way we store gas to prepare for a harsh winter as Russia shuts off the supply valves.

“There, we are in a drought record.

A huge quantity of water will be absorbed by the superficial soils and the vegetation, we are still far from filling the water tables”, deciphers Jean-Michel Soubeyroux.

The rain, however, moistens the upper layers of the soil, which will then be ready to let the water infiltrate to the groundwater.

In this experiment Dr Rob Thompson of @UniRdg_Met shows just how long it takes water to soak into parched ground, illustrating why heavy rainfall after a #drought can be dangerous and might lead to flashfloods.

@R0b1et @UniRdg_water pic.twitter.com/zbb3xLTXdK

— Uni of Reading (@UniofReading) August 10, 2022

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But "the filling of groundwater will not happen before the fall," insists the climate expert.

Especially since the meteorological institution predicts, after these few stormy days, the return to hot and dry weather.

"So this is perhaps the only opportunity we have to improve the situation in terms of the drought," explains Jean-Michel Soubeyroux.

Can these violent precipitations be dangerous? 

The intensity of precipitation, especially on dry ground, can however cause flooding.

"In the Mediterranean regions, the intensity of extreme precipitation has increased by 15% since the 1960s", underlines the climatologist.

Last year, the IPCC (Intergovernmental Panel on Climate Change) pointed out in its report that with global warming, torrential rains will be more frequent and intense.

For each degree of warming, the intensity of extreme precipitation increases by 7%.


Our climate report

The violent precipitation to come could therefore create floods while the dry soils act as an “aggravating factor”.

We must also keep an eye on another phenomenon: that of dry storms.

These storms, which carry little or no rain, can ignite the vegetation.

If lightning strikes dry soil and water-stressed vegetation, it can cause a natural fire.

This is what happened last Thursday in the Bouches-du-Rhône, in Auriol.

Lightning struck the Sainte-Baume regional park and ignited the dry vegetation around it.

And if lightning does not strike twice in the same place, our firefighters could find themselves on all fronts, between floods and forest fires.

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