Last October, the French groundwater tables showed generally high levels compared to the average.
The result of a very good recharge in the winter of 2021 and a rainy summer over a large part of the territory.
Eight months later, the situation has clearly deteriorated.
The BRGM, the national geological service, already pointed in May to groundwater levels which oscillated from "moderately low" to "very low" over a large part of the territory.
The situation had further deteriorated on June 1.
What to expect this summer?
Not easy to say.
Several factors come into play, from the rain that will fall to the water restrictions that will be taken, through the sensitivity of the groundwater to drought, not everywhere the same.
Nevertheless, the BRGM is rather pessimistic.
As of June 13, thirty-six departments were experiencing the first restrictions on water withdrawals and the orders in progress numbered 117, counts this Tuesday propluvial.fr, the ministerial site which lists them.
Just a start?
The Geological and Mining Research Bureau (BRGM), the national geological service, pointed out on Tuesday a problematic situation in several regions with regard to the level of groundwater tables on June 1.
Only the aquifers supplying Upper Normandy, the north of Ile-de-France and Picardy, as well as those in the north-east of the Occitanie region, are displayed in green, synonymous with "levels around the average". .
The north-west and north-east quarters, as well as Aquitaine, a good part of Burgundy and Auvergne are displayed in yellow, corresponding to moderately low.
The south of Alsace, the entire Rhône valley as well as the Touraine region and the north of Poitou-Charente are falling into orange, the level of their water tables being considered "low".
And there is also red.
"This is the Charente-Vendée sector, where the groundwater levels are already at a historically low level and therefore very worrying," says Violaine Bault, hydrogeologist at BRGM, in charge of the French groundwater situation bulletin that she produces every month. .
A France in blue last fall
However, everything had started rather well last October and November, when entering the groundwater recharge period.
A recharge mainly due to autumn and winter rains, when the vegetation is dormant.
A large part of the metropolis was then sky blue, a sign – reassuring – that the water tables were at a moderately high level compared to the average.
There were even some hints of darker blue, corresponding to high or even very high levels.
In the Center region and a large part of Occitania, the levels were considered average.
Only the Provence-Alpes-Côte-d'Azur (PACA) region and Languedoc-Roussillon could display areas in yellow and orange, the level of the groundwater there then being considered as "moderately low" or "low".
An early drought over much of France
It was then that the situation deteriorated.
“Water recharge in autumn 2021 and winter 2022 was very low on most groundwater, continues the BRGM hydrogeologist.
As of May 15, 2022, they were on average at -70% compared to a normal 100% recharge.
Only the south of the Adour-Garonne basin has a slight surplus, and Languedoc-Roussillon was also able to benefit from heavy rains during March.
Another significant fact: the recharging period ended very early on a large part of the territory.
"As of January-February, it stopped raining, and the level of the water tables began to drop from this period, two or three months earlier than usual", says Violaine Bault.
The water tables have since continued to empty, especially between May 1 and June 1, a usual trend in this period.
All the same, in one month, several regions (Aquitaine, the northeast quarter of France, the south of the Rhône valley) have switched from green – the average – to yellow – moderately low.
It is also not the first time that France has faced an early drought.
Violaine Bault cites the years 1976, 2005, 2017. “But also 2012, which most closely resembles the situation we know today, with low groundwater levels over practically the whole country”.
A summer that promises to be problematic?
The challenge is to know what we have in store for this summer, in terms of temperatures and precipitation.
Not easy to anticipate.
Already last year, Météo France was anticipating a hotter and drier than normal summer.
The reality had been quite different for a large part of France, with a very rainy month of July and a gloomy month of August.
Once again, Météo France predicts high temperatures for the coming season.
The BRGM is on the same wavelength, forecasting lower levels until mid-October to November, barring exceptional rainfall events.
The risk of drought is "high" over a large part of the metropolitan territory.
Even "very strong" in the Provence and Côte d'Azur regions, but also those of Poitou, Charente, Perche, Maine,
Conversely, the risk of drought is "low" in Upper Normandy and the Somme, in the north of the Grand Est region, in the departments of Savoie and Isère and in part of Occitanie.
“These are either sectors which have been well watered up to now, or with inertial layers, explains Violaine Bault.
The cyclicity of the water there is very slow, over several years.
They recharge and empty very slowly, so that they are ultimately not very sensitive to episodes of drought.
Quite the opposite of reactive aquifers, with the cyclicity of fast water.
“When it stops raining, they can drain in one to two months, which makes them very sensitive to drought,” continues the hydrogeologist.
It is the latter, overall, that go from yellow to red on the map on June 1st ”.
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Is there a risk of water shortage in France?
“In France, there is no shortage of water, on the contrary we have a lot of it,” replies Violaine Brault.
But the legislation, quite well done, makes every effort to guarantee a certain level of groundwater.
The stakes are crucial, because the flow of our waterways greatly depends on its groundwater.
"Between 80 and 100% for certain rivers in the summer, when there is no rain for several weeks," says Violaine Brault.
This groundwater also feeds the springs via exchanges with wetlands and is also heavily used for our drinking water supplies.
This is the whole risk then this summer: a cascade of prefectural orders restricting water withdrawals to guarantee a sufficient level of groundwater.
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