Hydrogeological situation on 1 May 2024
In April 2024, the overall trends were mixed. As the recharge period came to an end, the levels in reactive aquifers decreased in general, whereas the levels in inertial aquifers continued to rise.
The state of the aquifers was extremely satisfactory over a large part of France, particularly in the reactive aquifers, due to a 2023-2024 recharge surplus. The situation remained unfavourable, with low to very-low levels in the Sundgau inertial aquifer (southern Alsace) and in the aquifers in Aude, Roussillon and eastern Corsica.
The month of May should provide confirmation that the recharge period has come to an end. The state of the inertial aquifers should remain stable in May and then deteriorate slowly until the autumn. The rate of change to the levels in reactive aquifers will essentially depend on cumulative rainfall, evapotranspiration and the demand for water. The situation should be closely monitored in aquifers which currently have low to very-low water levels, as well as in areas where abstraction demand is particularly high.
Map of aquifer levels in mainland France on 1 May 2024.
© BRGM
Evolution of the trends observed on piezometers from September 2023 to April 2024.
© BRGM
Groundwater trends
In 2023, the recharge started late (at the end of October), but then remained extremely active across two thirds of the north of France and in the south-west. Significant rises in level were observed in the aquifers in the south-south-east of France as of the end of February. At the end of March, the 2023-2024 recharge was far greater than normal across a large part of the country, except along the coastal areas of the Languedoc and Roussillon regions and in Corsica.
In April 2024, the trends began to reverse at varying degrees across the country, marking the end of the recharge period. Levels had risen in 44% of observation points and had fallen in 39% (compared to 64% and 16% respectively in March).
During the spring, dormant vegetation begins growing again and absorbs a large proportion of the water that seeps into the ground. Consequently, rainfall has little effect on aquifer recharge during this period. The trends observed in April were therefore mainly due to total local rainfall over the period and whether the aquifers have a high or low degree of recharge inertia.
The levels continued to rise in the inertial aquifers in the Artois area, Paris Basin, Sundgau region and Rhône-Saône corridor. These aquifers take a long time to react to effective rainfall. The recharges in April were linked to the gradual infiltration of rainfall from late winter and early spring. However, the recharge rate diminished in intensity at the end of the month and levels appeared to be stabilising.
The trends observed in April in reactive aquifers essentially depended on effective local rainfall. Consequently, levels rose in the alluvial aquifers in the south-east and in the tertiary formations in the valleys of the Alps, Lower-Rhône, Durance and Côte d'Azur. A significant recharge episode was recorded at the beginning of April, further boosted in certain areas by a less abundant episode at the end of the month. Elsewhere, the aquifer depletion period gradually began to take a foothold. Aquifer levels were stable in the north-east of France and Languedoc, due to rainfall at the end of March and April. Levels fell slightly in the reactive aquifers of the western two-thirds of the country and in Corsica. Finally, there was insufficient rainfall in April on the Roussillon plain and in the Corbières massif to significantly recharge the aquifers.
Comparison between 1 May 2023 and 1 May 2024
Map of France showing the state of the aquifers on 1 May 2023 (left) and 1 May 2024 (right).
© BRGM
Evolution of the situation observed on piezometers from September 2023 to April 2024.
© BRGM
The groundwater situation
The aquifer situation during the low-water period in 2023 was unsatisfactory, with levels being generally below monthly norms. The significant recharge that occurred as of the end of October 2023 had a marked effect on the aquifers. Successive recharge episodes during the winter and spring kept the levels of reactive aquifers well above normal. The overall situation improved slowly in the inertial aquifers but their respective states varied in March.
In April 2024, the situation continued to improve compared with the previous month. The overall state of the aquifers was very satisfactory. The levels recorded at 22% of the observation points were below monthly norms, 13% were comparable with monthly norms and 65% were above them (compared with 27%, 15% and 58%, respectively, in February). The situation was more positive than that observed for the previous year, in April 2023, when 68% of the levels recorded were below monthly norms. Only the aquifers in the Pyrénées-Orientales and Corsica had levels that were lower than in April 2023.
The 2023-2024 recharge surplus was far greater than normal in almost all of the aquifers in France and the spring rains sustained this active recharge, resulting in current levels that are mostly close to monthly norms or very high. The varying state of the different aquifers across the country is mainly due to the local intensity of the 2023-2024 recharge and the speed with which each aquifer reacts to infiltrated rainfall.
The state of the inertial aquifers changed very little between March and April 2024, with recharge slowing down during April. High to very-high levels were recorded in the chalk aquifer in the Artois basin and the aquifer in the Savoy foothills, following a low-water period in 2023 that was not very severe and an exceptionally high recharge surplus in 2023-2024. The state of the aquifers in the Paris Basin remained variable; it was positive in the upstream areas, with moderately-high to high levels, and less favourable in the south-west, with levels close to normal to moderately low. The situation deteriorated in certain areas, with moderately-low to low levels in the Beauce aquifer and locally in the Normandy chalk aquifer to the south of the Seine. The Sundgau aquifer (in southern Alsace) remained low, due to its high degree of inertia. Finally, the aquifers in the Saône and Rhône corridors had levels that were moderately low or close to normal monthly averages. Unfavourable situations were observed locally, notably in the Dombes, the East Lyon area and the north of the Drôme.
The situation was highly satisfactory in many reactive water tables. The state of the aquifers remained generally stable compared to March. There was a slight improvement in certain areas that had received a lot of rain: on the eastern and southern edges of the Paris Basin, in the central-northern part of the Massif Central, the Saône valley and the Jura. The situation deteriorated in a few highly reactive aquifers in the south-west, which were affected by a lack of rainfall.
In the northern two-thirds of the country and in the south-west, the overall levels in April were moderately high to very high, due to the recharge surplus in 2023-2024 and further boosted by rainfall in the spring. In areas that experienced less favourable scenarios, the levels were near normal to moderately low. The aquifers in the Alsace and Limagne plains, and below the volcanoes of the Massif Central, had a less significant recharge and are less reactive to rainfall. In the south-west, the start of the depletion period was observed in certain aquifers as early as March. Negative situations were more marked in certain localised areas, with moderately-low levels noted in the south of the Causses du Quercy and to the west of the Grands Causses.
Until late February or early March, the state of the aquifers in the south-south-east remained worrying. Recharge episodes in March and early April considerably improved the situation. In April, aquifer levels were very satisfactory – ranging from moderately high to very high – in the southern Massif Central, Bas-Rhône, Provence and Côte d'Azur. Along the Languedoc coast, rainfall infiltration remained insufficient to make up for the lack of rain recorded since autumn 2023. Here, the aquifer levels were not very satisfactory, ranging from close to normal to very low. Finally, the rainfall had no impact on the aquifers in the Corbières Massif and in the Roussillon plain, and levels remained worryingly low. The situation in Corsica varied locally, with low to very-low groundwater levels observed in the aquifers along the northern and eastern coasts.
Aquifers that are in a very good state
Several aquifers were in a very good state, with levels being high to very high compared to the levels recorded for April in previous years:
- The aquifer levels recorded in the Artois basin are due to overly-abundant recharges in 2022-2023 and 2023-2024;
- The reactive aquifers on the eastern and southern edge of the Paris Basin (chalk aquifer in the Champagne area, Albian-Neocomian sand aquifers and Jurassic limestone aquifers) had high to very-high levels, due to a surplus recharge;
- The situation was highly satisfactory in the south-western coastal area, in the aquifers in the eastern and southern part of the Armorican Massif to the central part of the Aquitaine Basin, due to the abundant rainfall recorded since mid-October 2023.
Aquifers in a poor state
Several aquifers were in a poor state with low to very-low levels compared with April in previous years, due to a marked lack of rainfall in recent months, or even over recent years:
- The level of the inertial aquifer in the inertial Plio-Quatenary gravel aquifer of the Sundgau region remained low, due to its very inertial behaviour;
- The levels in the Aude alluvial aquifer also remained low, since the rainfall in March 2024 did not make up for the generally low recharge rate since the autumn of 2023;
The state of the multi-layer aquifer in Roussillon and the karst limestone aquifers in the Corbières massif remained extremely poor, with very low levels, due to a lack of rainfall over the last two years.
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
Forecasts
The Météo-France seasonal forecasts for May, June and July do not suggest any particular scenario in terms of rainfall, but temperatures are expected to be higher than normal across France.
Over the next few months, most of the water that filters down through the soil will be consumed by vegetation and will therefore not seep far down into the ground. Consequently, depletion should start in May in all aquifers in France. This should continue until the vegetation becomes dormant, – i.e. until October or through to the end of November – and/or until there is abundant rainfall. However, only occasional, local recharge episodes are likely to occur during the summer. In order for the state of aquifers to improve and their levels to increase, there will need to be significant rainfall on ground that is already damp. Moreover, this will only improve the situation in reactive aquifers. The demand on water resources through abstraction may also affect the state of the aquifers.
In May, if there is not enough rainfall, all the aquifers across the country will probably see the onset of depletion. In this case, levels will probably remain low and the situation will therefore deteriorate. The effects will be rapidly felt in the most reactive aquifers as well as those with the highest abstraction rates, but more slowly in inertial aquifers, or aquifers whose resources are exploited less.
As regards inertial aquifers, any rainfall that occurs in May is unlikely to generate a significant recharge. The overall trends are expected to stabilise, with depletion likely to begin in May and continue until autumn, unless there are exceptional rainfall events during this period. The situation in the inertial aquifers should therefore remain stable in May and then deteriorate gradually through the summer. Groundwater abstraction could accelerate the depletion of these aquifers and particular unfavourable situations could therefore arise locally.
As regards reactive aquifers, the trends in May and over the next few months will depend on total local rainfall, evapotranspiration and the demand on water resources. The snow melt at the end of spring will also affect the aquifers in the Pyrenees and Alps. Significant rainfall episodes could result in brief recharges. This could therefore maintain certain aquifers' levels and may even, very occasionally, cause levels to rise. As such, the situation may remain stable or could even improve locally. However, any deep infiltration will be limited if the ground is dry, since the rainfall will simply moisten the soil and be consumed by the vegetation. Significant rainfall could also reduce excessive demand on groundwater resources, notably for irrigation. If there is insufficient rainfall, the depletion of the reactive aquifers will probably continue in May. As a result, the situation is likely to deteriorate. The rate of depletion will be faster in more reactive aquifers and/or in aquifers which are exploited more intensely for abstraction. If there is no rain and temperatures are high, the early start of irrigation campaigns could also affect the state of the aquifers.
However, the forecasts for the coming months are positive for most aquifers. That being said, certain areas will need to be particularly closely monitored, since current levels are not sufficient to guarantee satisfactory levels over the summer. Again, there is still some uncertainty, since local situations will depend on total local rainfall over the coming months and therefore the need for abstractions from certain aquifers. The aquifers that need to be particularly monitored are in the following areas: the south-eastern part of the Paris Basin (the area south of the Seine, the chalk aquifer in Normandy, the Beauce aquifer, the Cenomanian sand aquifers in the eastern part of the Pays de la Loire and Centre-Val de Loire regions), southern Alsace (Sundgau), the corridors of the Saône (Bresse and Dombes) and Rhône rivers (eastern Lyon and northern Drôme), the Limagne plain, the Chaîne des Puys, the south-western part of the Massif Central (between the southern Causses du Quercy, the western Grands Causses and the Montagne Noire), the Pyrenees, the Languedoc and Roussillon coastal areas and Corsica.
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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.
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Map drawn up by BRGM on 14 May 2024, based on data from the ADES database, acquired up to 30 April 2024. Data source: ADES database (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.