Drought: at the start of summer, groundwater and watercourses are in a mixed state

Despite the storms that swept across France during the night from Wednesday to Thursday, causing flooding here and there, another, more insidious threat continues to weigh on many areas: drought. "Torrential rains will tend to fall violently to the ground instead of infiltrating it, and to run off," emphasizes hydrologist Emma Haziza, adding that "a flooded area will not necessarily be spared from drought."

Faced with the drought, water restriction orders have been increasing since mid-June, and even since the end of May in some municipalities. This Friday, June 27, it is the turn of the Nord department to increase vigilance in the face of "high" risks of "tension on the drinking water supply" and the "sharp drop" in river levels, the prefecture explained. The cause is a "record deficit" of precipitation this spring, with the February-March-April quarter being the driest observed by Météo France in the Hauts-de-France region since 1959.

Without necessarily reaching these extremes, the northern half of France experienced a notable rainfall deficit this spring. This phenomenon is partly linked to the presence of high pressure systems over the British Isles, which chased away the disturbances, while the south remained exposed to bad weather arriving from the Mediterranean basin.

This meteorological peculiarity allowed the prefect of the Pyrénées-Orientales , a department subject to a historic drought for more than two years, to lift certain water restrictions at the end of May. But the official had to backtrack on June 24, noting "a further drop in the flow rates of most watercourses" and "a drop in the level of certain water tables." Several measures, now well known to residents, are once again in force: the reduction of agricultural water withdrawals, the ban - total or partial - on watering gardens, green spaces and golf courses, but also on washing vehicles.

The drought observed in certain areas at the start of summer is affecting both surface water reserves—some rivers are already temporarily dry—and groundwater reserves. Warm colors now dominate the map detailing the state of groundwater from the Bureau of Geological and Mining Research (BRGM), the latest version of which was published on June 15. In addition to the Pyrénées-Orientales, the Aude region is also in a critical situation, as is a large swathe of territory running from the Ardennes to northern Burgundy.

While 80% of groundwater levels are falling nationally, the lack of rain doesn't explain everything. "We've been experiencing temperature anomalies lately," insists Emma Haziza, also president of the Mayane Residence Center, a player in environmental education and sustainable development. "The hotter it gets, the more plants pump water from the water tables to transpire it." Heat waves , which are occurring earlier and more intensely due to global warming, are thus exacerbating drought.

If the summer is hotter and drier than normal, as forecast by Météo France, the situation could become critical in certain areas. BRGM's forecasts for the Roussillon plain are thus "very pessimistic" , while they remain more "uncertain" for other aquifers.

In addition to the Pyrénées-Orientales, decrees have placed certain municipalities in two other departments in a state of "crisis," a status that provides for the most severe water restrictions: the Ardennes and Loiret. And the situation remains very mixed in the Paris basin and eastern Lyon, where the BRGM predicts that water table levels will be "above normal" this summer.