Depletion of aquifers due to a lack of effective rainfall in April
Across the country, the lack of effective rainfall in April meant that aquifers with quick response times continued to empty. Levels dropped in 79% of the aquifers, although they remained satisfactory in the majority of cases, with the levels at 66% of the observation points remaining above monthly norms. The aquifers located in certain geological formations in the Grand Est, Cotentin and Boulonnais regions and in the Massif Central had moderately low levels.
The situation was worse than in April 2025, particularly in less responsive aquifers, when 76% of observation points were above or around monthly norms.
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, considering the water needs of vegetation and the gradual increase in demand for water to satisfy various uses, particularly agricultural needs, it is difficult to know if any potential rainfall in May will have a positive effect on the levels, and how that rainfall may be distributed across France. The outlook for the longer term therefore remains uncertain.
Map of aquifer levels in mainland France on 1 May 2026.
© BRGM
Evolution of the trends observed on piezometers from April 2025 to April 2026.
© BRGM
Trends
After an initial period of depletion observed in many aquifers in March, there was a general downward trend in groundwater levels across virtually the whole of France in April. This was due to a significant lack of effective rainfall over the period, with values well below seasonal averages.
As a result, the majority of aquifers are currently being depleted.
The data collected in April 2026 highlighted that depletion was in progress at 79% of the observation points, which showed decreasing levels. Levels were stable at 11% of the observation points. Only 10% showed rising levels. The intensity of the beginning of this depletion period appears to be slightly greater than that recorded in April 2025.
Aquifers with slow response times
Aquifers with very slow response times were still recharging at the beginning of April 2026, but some of these saw their dynamics reverse during the course of the month. The aquifers in the chalk formations of Normandy and in the Ypresian sand and Lutetian limestone formations in the Paris basin, as well as the Brie limestone aquifers, have entered a depletion phase. Other aquifers with slow response times continued to show stable or rising levels, although the pace of increase seemed to be slowing at the end of April.
Aquifers with quick response times
The lack of effective rainfall in April accentuated the depletion of highly responsive aquifers. All of these aquifers had declining levels, with the notable exception of the Jurassic limestone aquifers of the Brenne and Vienne basins, the aquifers in the volcanic formations of the Massif Central and the alluvial aquifers of the Alpine valleys, as well as in the Astian sand aquifers of the Valras-Agde region, where levels remained stable.
Comparison between 1 May 2025 and 1 May 2026
Map of France showing the state of the aquifers on 1 May 2025 (left) and 1 May 2026 (right).
© BRGM
Evolution of the situation observed on piezometers from April 2025 to April 2026.
© BRGM
Overall groundwater situation
At the beginning of April, piezometric levels were generally satisfactory throughout France, with the notable exception of the aquifers in the Grand Est region and the Limagne plains. The lack of rainfall in April led to a fall in groundwater levels overall.
At the end of April 2026, groundwater levels were satisfactory, with 66% of observation points in line with or slightly above monthly norms. The levels recorded at 34% of the observation points were below monthly norms, 26% were comparable with monthly averages and 40% were above monthly norms (compared with 16%, 22% and 62%, respectively, at the end of March).
The current situation appears to be worse than that observed at the end of April 2025, when 27% were below monthly norms, 23% were comparable with monthly averages and 50% of levels were above.
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 even had moderately high levels compared with the average, notably the limestone aquifers in the Beauce and Armagnac regions and the fluvio-glacial alluvial aquifers in the eastern Lyon area and the Savoie foothills.
It should be noted that significant localised differences were observed within these aquifer systems.
Aquifers with quick response times
The situation in extremely responsive aquifers remained satisfactory throughout the country. Piezometric levels were around monthly norms in the majority of cases, with the exception of the Albian sand aquifers on the eastern edge of the Paris Basin, the Jurassic limestone aquifers in Lorraine and the Côte des Bars, the sandstone aquifers of the Vosges, the Triassic limestone aquifers in Lorraine and the Limagne plains and the aquifers in the volcanic formations of the Massif Central, which already had moderately low levels on 15 April.
The levels in the chalk aquifers of Champagne, the bedrock aquifers of the Cotentin-Sarthe area and the Limousin region, as well as the Jurassic limestone aquifers of the Bessin region and the Causses du Quercy were slightly below monthly norms.
High piezometric levels continued to be observed in the alluvial aquifers of the Garonne, Aude, and Rhône basins, in the Roussillon plain and Vistrenque basin.
Key figures
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79.00%of levels decreased
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40.00%of levels were above monthly averages
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34.00%of levels were below monthly averages
Forecasts
Météo-France's seasonal forecasts for the period of May-July 2026 indicate an increased likelihood of above-normal temperatures across the country. However, no clear scenario has been identified for rainfall patterns.
The regrowth of vegetation, combined with high temperatures, will limit the amount of rainfall that filters deep into the earth, due to increased evapotranspiration. All highly responsive aquifers are currently entering the depletion period. Even certain aquifers with very slow response times are beginning to show a downward trend in terms of their levels.
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.
The recharge is expected to continue or to stabilise during May in the less-responsive aquifers in the Artois and Sundgau (southern Alsace) regions and along the Rhône-Saône corridor, due to the late infiltration of rainfall from February. Consequently, their hydrogeological situations could improve or remain stable, depending on the volume of water that filtered deep into the earth.
As regards other slow-response aquifers, in which downward trends have already been observed, there is a degree of uncertainty as to the effectiveness of the spring rainfall and exactly when the recharge period will end. 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 April accentuated the 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, since their levels will depend on the effectiveness of spring rainfall, the needs of vegetation, and human withdrawals for various uses, in particular irrigation, which has already begun. The spring rainfall will play an essential role in maintaining levels above normal for as long as possible. In the event of a prolonged and intense drought, the more responsive aquifers could empty in a matter of weeks. 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 10 May 2026, based on data acquired up to 30 April 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.