The depletion of aquifers continued, due to a lack of effective rainfall in May
As in the previous month, the depletion of groundwater in aquifers continued across the whole of France, due to the lack of effective rainfall in May, particularly during the last two weeks of the month. Nonetheless, most groundwater levels remained satisfactory.
Low levels were recorded in the aquifers in the Jurassic limestone formations of Lorraine and in the karst limestone formations of the Causse du Quercy, as well as in the Limagne plains, whereas high to very-high levels were observed in the alluvial aquifers of the Roussillon plain, the lower Rhône and the Vistrenque basins.
The situation was worse than on 1 June 2025, particularly in less responsive aquifers, when 69% of observation points were above or around monthly norms.
With 58% of observation points with levels around or above monthly averages, the overall groundwater situation remained satisfactory. However, the volume of groundwater in the aquifers continued to decrease. The most responsive aquifers, or those which had only benefited from a moderate recharge, were below normal monthly levels.
The provisional assessment of the 2025-2026 winter recharge period suggests that we can expect satisfactory levels in the majority of the responsive aquifers in the south-west and south of France over the next three months. However, it is difficult to know how the summer rainfall will be distributed across France and whether it will be sufficient to re-humidify the soil and thus reduce the amount of groundwater that needs to be abstracted for various uses, particularly agriculture. The outlook for the longer term therefore remains uncertain.
Map of aquifer levels in mainland France on 1 June 2026.
© BRGM
Evolution of the trends observed on piezometers from May 2025 to May 2026.
© BRGM
Trends
The groundwater depletion observed in April continued in May. Generally speaking, the piezometric levels of the aquifers fell across most of the country. This can be explained by the lack of rainfall across the whole country in May, with a particularly marked period of drought in the second half of the month. Only the northern part of the Armorican Massif, the Cévennes, the Alps and the Jura had a slight surplus of effective rain, due to the rain that fell at the beginning of May.
The data collected in May 2026 showed that depletion was in progress at 77% of the observation points, which showed decreasing levels. Levels were stable at 15% of the observation points. Only 8% showed rising levels. The degree of depletion appears to be slightly greater than in May 2025.
Aquifers with slow response times
In May 2026, the levels continued to decrease in aquifers with very slow response times, in which depletion had already begun. This was notably the case for the limestone aquifers in the Beauce, Artois and Normandy regions and in the aquifers in the Lutetian formations and Ypresian sands in the Paris Basin.
The aquifers in the Bresse and Dombes regions, whose levels had stabilised in April, began to decrease in May.
The situation in other aquifers whose levels had stabilised or were rising in April remained the same. This was notably the case in the aquifers in the Armagnac limestone formations, the Sundgau gravel formations and the fluvio-glacial formations in eastern Lyon, as well as in the Dauphiné region and the Savoie foothills.
Aquifers with quick response times
The depletion continued due to the lack of rain at the start of May – or the fact that the rain had little effect in terms of recharge – and the very dry spell during the second half of the month. Levels decreased in almost all the aquifers. Only the alluvial aquifers in the valleys of the Alps and the Durance registered slight rises. Levels were stable in the aquifers of the Aquitaine Basin, in the alluvial aquifers of the Adour and Gave de Pau rivers and in the lower Rhône. They were also stable in the limestone formations of the Corbières Massif, the basement formations of the Cévennes, the volcanic formations of the Massif Central as well as in the Vistrenque basin and the sands of the Roussillon plain.
Comparison between 1 june 2025 and 1 june 2026
Map of France showing the state of the aquifers on 1 June 2025 (left) and 1 June 2026 (right).
© BRGM
Evolution of the situation observed on piezometers from May 2025 to May 2026.
© BRGM
Overall groundwater situation
At the beginning of May, the groundwater situation remained satisfactory, except in the Grand Est region, Cotentin, the Limagne plain and the western part of the Massif Central. Due to the marked lack of rainfall in the 2nd half of May, the situation deteriorated.
At the end of May, groundwater levels were satisfactory, with 58% of observation points slightly above or around monthly norms. A total of 42% of observation points were below normal. More specifically, 30% of observation points were above normal, 28% were comparable with monthly norms and 42% were below normal (compared with 40%, 26% and 34% respectively at the end of April).
The current situation appears worse than that observed at the end of May 2025, when 46% of levels were above monthly norms, 23% were comparable with monthly averages and 31% were below.
Aquifers with slow response times
The levels in aquifers with extremely slow response times remained satisfactory overall. Most of these aquifers had levels close to monthly averages. Certain aquifers had moderately high levels in relation to monthly norms, namely the aquifers in the limestone formations of the Beauce and Armagnac regions.
It should be noted that significant localised differences were observed within these aquifer systems.
Aquifers with quick response times
The situation in highly responsive aquifers was variable. Some had moderately low levels, for example the aquifers in the north-eastern Jurassic arc of the Paris Basin, in the basement formations of the Cotentin and western Brittany and in the Massif Central. This was also the case in the limestone formations of the Charentes and Triassic limestone formations of Lorraine, as well as in the sandstone formations of the Vosges, the alluvial aquifers in the northern Alsace plain, the fluvio-glacial alluvial aquifers of the upper Rhône and those in Corsica.
Low levels were recorded in the aquifers in the Jurassic limestone formations of Lorraine and in the Limagne plain as well as in the karst limestone formations of the Causses du Quercy.
Levels remained moderately high in the aquifers in the Aquitaine Basin, in the chalk formations of Touraine, the Jurassic limestone formations in the Vienne region and in the limestone formations of the Grands Causses. They were also moderately high in the sands of the Valras-Agde area and in the alluvial aquifers of the Hérault and Garonne rivers. Levels were high to very high in the alluvial aquifers of the Roussillon plain, the lower Rhône and the Vistrenque basin. Levels were around normal in the other responsive aquifers around the country.
It should be noted that significant localised differences were observed within these aquifer systems.
Key figures
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77.00%of levels decreased
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30.00%of levels were above monthly averages
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42.00%of levels were below monthly averages
Forecasts
Météo-France's seasonal forecasts for the period between June and August 2026 indicate an increased likelihood of above-normal temperatures across the country. However, no clear scenario has been identified for rainfall patterns.
The water required by plants, due to higher temperatures, could reduce the amount of rainfall that seeps deep into the ground. In this case, depletion will continue in almost all aquifers.
Aquifers with slow response times
The levels in less-responsive aquifers depend on the levels reached during the previous low-water period and on the total amount of effective rainfall during the entire recharge period.
Only the limestone aquifers in Sundgau and Armagnac regions still have rising levels. In June, therefore, the levels in the other aquifers are expected to fall or remain stable, in certain cases, and then continue to decrease until the autumn.
However, the outlook for the summer of 2026 remains uncertain. Piezometric levels will certainly be lower than those observed in 2025, due to a less abundant recharge in 2025-2026.
Aquifers with quick response times
The lack of effective rainfall in May, especially in the 2nd fortnight, resulted in the continued depletion of responsive aquifers. Nevertheless, the seasonal forecasts remain positive for the responsive aquifers that currently have moderately high to high levels.
As regards the other responsive aquifers, in which levels are currently around or slightly below monthly norms, the outlook remains uncertain and will depend on summer rainfall. If there is sufficient rain this could re-humidify the soil and reduce the need to pump water from aquifers for different uses (notably drinking water and agricultural irrigation).
Highly responsive aquifers are sensitive to prolonged and intense droughts. Consequently, the outlook for the longer term, notably for the end of summer 2026 and the low-water period, remains uncertain.
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State of groundwater: monitoring by BRGM
Groundwater is a widely used resource: in metropolitan France, it accounts for nearly two-thirds of drinking water consumption and more than one-third of agricultural water consumption. It is also widely used in the industrial sector. Groundwater tables depend on cyclical recharges.
BRGM monitors groundwater levels and quality in mainland France. Discover the actions carried out by the French geological survey and the resources and databases available on groundwater in France.
Aquifer recharge: 3 questions to provide a better understanding of the process
How do aquifers fill up and how do they empty?
Groundwater levels vary throughout the year, from high levels in winter (when vegetation does not absorb rainwater) to low levels in summer (the traditional depletion period).
The fate of rainfall varies greatly depending on the time of year and the condition of the ground surface on which it falls. Usually, the groundwater-recharge period takes place from early autumn (September-October) to early spring (March-April), a six-month period during which vegetation is dormant (with low evapotranspiration) and rainfall is generally more abundant. If the winter is dry, groundwater recharge is very low.
From spring through summer, rising temperatures coupled with the regrowth of vegetation and thus increased evapotranspiration, limit the infiltration of rainfall into aquifers. Between May and October, unless there are exceptional rainfall episodes, aquifer depletion usually continues and levels will keep decreasing until the autumn.
Why do some aquifers recharge faster than others?
Groundwater flows at different rates depending on the porosity (percentage of gaps/cracks in the rock) and permeability (capacity to allow water to circulate, i.e. interconnectivity between these gaps/cracks) of the aquifers. The larger the gaps and the more interconnected they are, the faster the water will flow, for both refilling and depletion.
It takes a given volume of water different periods of time to travel the same distance, depending on the kind of rock formation:
- a few years in a porous formation,
- a few months in a cracked formation,
- and a few days, or even a few hours, in a karst formation.
Inertial and reactive aquifers: what are they?
The impact of the winter recharge varies according to the cyclic nature of the aquifer, i.e., its reactivity to rainfall infiltration.
We refer to aquifers that are:
- reactive (when they are composed of sand, gravel, karst limestone or weathered granite formations). These aquifers are characterised by their rapid reaction times: they can recharge during heavy summer rainfall, but are also highly sensitive to drought. Their levels can therefore vary very quickly over the course of the same season.
- inertial (when composed of chalk, non-karst limestone, sandstone formations). Their reaction times are slow. They can have multi-annual cycles, meaning that they require a long period to recharge or empty.
Cyclicity of aquifers in mainland France.
© BRGM
Map drawn up by BRGM on 4 June 2026, based on data acquired up to 31 May 2026.
Data source: ADES (ades.eaufrance.fr) / Hydroportail (hydro.eaufrance.fr) / Background map © IGN. Data producers and contributors: APRONA, BRGM, Conseil Départemental de la Vendée, Conseil Départemental des Landes, Conseil Départemental du Lot, EPTB Vistre Vistrenque, Parc Naturel Régional des Grandes Causses, Syndicat Mixte d’Etudes et de Travaux de l’Astien (SMETA), Syndicat Mixte pour la protection et la gestion des nappes souterraines de la plaine du Roussillon (SMNPR).
This map shows the global indicators reflecting the average fluctuations of the aquifers. They are based on point indicators collected at groundwater monitoring points (by means of piezometers).
The "Aquifer levels" indicator compares the current month’s figures with those of the same months in the entire record, i.e. at least 15 years of data and sometimes up to as much as 100 years of data. It is divided into 7 classes, from the lowest level (in red) to the highest (in dark blue).
The grey areas correspond to areas without unconfined aquifers, i.e. with an impermeable or semi-permeable layer above the aquifer, and/or sectors with a very low density of measuring points. This last case primarily concerns mountainous areas with small, heterogeneous aquifers.
The "Evolution of levels" indicator reflects the variation of the water level of the past month compared to the two previous months (stable, increasing or decreasing).
These global indicators reflect general situations and trends and do not take into account possible local disparities.