The rain is desired. Spring has only been here for a month but many professionals, especially farmers, are already worried: the drought is back in France. A dozen departments have taken measures to preserve water resources after the lack of rainfall in recent months. For some territories, the summer sequence could even turn out to be catastrophic. Update on the situation in the four corners of France, in the Paca, Occitanie, Pays-de-la-Loire and Grand-Est regions.
The south-east is already under great tension
In the Provence-Alpes-Côte d’Azur region, the sky was covered with welcome clouds this weekend. But the expected rainfall will not cover the hydrological deficit recorded in recent months. “Most of the precipitation will be captured by the vegetation and will not allow groundwater recharge”, notes Florian Gibier from Meteo France Paca. If the rainfall deficit is unevenly marked throughout the region, with a lack of between 100 and 200 mm depending on the department, the most worrying index on the eve of summer and the fire season remains that of the soil moisture. This index, which should rise slightly after the rains this weekend, is “at the level of record lows for the period and worthy of a summer”, continues Florian Gibier.
As a result, several cities are already experiencing water use restrictions, particularly in the Alpes-Maritimes where the prefecture has placed more than two thirds of the municipalities, including Nice, Antibes and even Menton, on “drought alert”, since March 31. A decision which is accompanied by constraints on the watering and filling of swimming pools in particular. The decree runs until April 30 and “the measures currently in force will be extended”, announce the state services, pending the next “meeting of the water resource committee”. The restrictions “will be adapted if necessary according to the actual level of precipitation” that the weather forecasts announce “significant in the coming days and next week”, further notes the prefecture.
In the Southwest, the worst avoided… for now
In the vast Adour-Garonne basin, from the Charentes to the Aveyron causses, the winter rains – the most effective because they do not evaporate – were relatively late (concentrated in December and January). They were even abnormally scarce from the Landes to the Charentes and from the Dordogne to the Lozère. This last department even experienced one of the driest months of January since 1959. In the aftermath, a drier month of February than normal throughout the basin further hindered the replenishment of groundwater.
Fortunately, an ordinarily rainy month of March made it possible to curb this negative dynamic. Overall, the situation is worse than over the past two years, but better than in 2019. It is also geographically contrasting: water reserves are generally satisfactory in the Garonne basin, while in the Charente part, the Aquitaine coast and the eastern causses, the levels are already low.
A worrying lack of rain in the west
Who said it rains all the time in the west of France? In Pays-de-la-Loire, rainfall has already been below normal for five consecutive months. And the observation could well be repeated at the end of April, even if the rains of the first part of the month did “a lot of good”, observes Stéphanie Poligot-Pitsch, head of hydrometry at the Dreal. Inevitably, this deficit is not without consequence on the situation of watercourses. The flow of most of them, in particular the Loire and its tributaries (Sèvre, Erdre, Maine, Cher, etc.), is around 50% lower than the average flow for the month of April.
“It is relatively important, of course, but, at this time of the year, abundant rains could still make it possible to correct this deficit. Conversely, if the trend continues in the coming weeks, the situation could worsen. “At the level of groundwater, the same story, namely insufficient underground recharge and “unfavorable” levels at the start of spring, according to the Bureau of Geological and Mining Research (BRGM). Vigilance is already required for the most sensitive aquifers affected by drinking water catchments.
A lack of water but no worries for the moment in Alsace
Autumn and winter were also rather dry in Alsace. “It’s been more than six months since we’ve had significant rain,” confirms Christophe Mertz, one of the co-founders of Atmo-Risk, an Alsatian weather forecasting start-up. In its Entzehim station, near Strasbourg, for example, it lacks “about thirty millimeters to be normal”. The situation is worse in some places in the region. As a result, “the soils are abnormally dry”. And the Rhine water table lower than usual. Especially, in the south of Alsace.
“Between Mulhouse and Sierenzt and at the foot of the Vosges foothills,” explains Fabien Toulet, in charge of the rainfall network at the association for the protection of the water table of the plain of Alsace (Aprona). “In the sectors where the water table is shallower, that is to say north of Colmar, the two episodes of rain at the end of March and April 8-9 made it possible to recharge it temporarily. The situation is almost normal. “But as his colleague, the specialist assures him, it will have to rain in the coming weeks to avoid water restrictions this summer.