Hydrogeological situation on 1 June 2024
While the depletion period appeared to have already started in April, many aquifers benefited from late recharge episodes in May. The situations varied depending on the amount of local rainfall and how reactive the aquifers are.
Due to the extremely abundant recharge in 2023-2024, which lasted until May, groundwater levels were extremely satisfactory over a large part of the country in May. Levels were generally above monthly norms. Only highly inertial aquifers (Beauce, Sundgau, Bresse and Dombes) or areas in which the recharge was insufficient (Roussillon, Aude and Corsica) recorded unsatisfactory levels.
The end of the recharge period should start to take hold across the majority of the country during the month of June, unless there are further episodes of intense rain. The current situation is very favourable and suggests that levels will be above normal over the next few weeks. However, the situation needs to be closely monitored in aquifers that have moderately-low to very-low water levels at the moment, as well as in areas where abstraction demand is particularly high.
Map of aquifer levels in mainland France on 1 June 2024.
© BRGM
Evolution of the trends observed on piezometers from October 2023 to May 2024.
© BRGM
Groundwater trends
The 2023-2024 aquifer recharge was far greater than normal across a large part of the country, except along the western part of the Languedoc and Roussillon coastal areas and in Corsica. During the spring, dormant vegetation starts 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. However, there was sufficient rainfall in the spring of 2024 to keep the soil moist and meet the water needs of the vegetation. Consequently, rain was able to filter deep into the ground and maintain levels or even recharge certain aquifers in April and May 2024.
In May 2024, the trends varied across the country, but the rain continued to recharge many aquifers. Levels had risen in 38% of observation points and had fallen in 39% (compared to 44% and 39% respectively in April).
Inertial aquifers take a long time to react to effective rainfall. The trends observed in these aquifers in May reflected the infiltration of rainfall that occurred during late winter and spring. As regards the aquifers in the Artois basin, the seasonal depletion period started during the month of April and the levels therefore dropped in May. In the Paris basin, the trends varied, with levels generally stable in the western regions and rising in the eastern and southern regions. The winter recharge continued to slow and the depletion period seems to be gradually establishing itself. Finally, in the Sundgau (southern Alsace) and the Rhône-Saône corridor, the recharge remained active, but started to slow down in the least inertial areas.
The trends observed in May in reactive aquifers depended on effective local rainfall. The depletion period began in April and continued in May in many areas: the edge of the Paris Basin, the Armorican Massif, the west of the Aquitaine Basin, Provence, the Côte d'Azur and Corsica. However, the depletion rate was often minimal due to the contribution of infiltrated rainfall. The areas in which stable or rising aquifer levels were observed benefited from significant effective rainfall in May, notably in the strip of land stretching from Alsace and Lorraine to the Languedoc coast as well as in the upper Garonne valley, the Jura and Massif Central. These inflows helped maintain the water levels or led to a momentary, slight recharge of the aquifers. It should be noted that the aquifers in the Roussillon region recorded very small rises in levels at the end of April and beginning of May. Only the aquifers in the western two-thirds of the Massif Central and the eastern Languedoc recorded significant recharges, in particular the aquifers in the Limousin bedrock, the aquifers of the Limagne plain, the aquifers below the volcanoes in the Massif Central and the karst Jurassic limestone aquifers of the Causses du Quercy and the bordering area.
Comparison between 1 June 2023 and 1 June 2024
Map of France showing the state of the aquifers on 1 June 2023 (left) and 1 June 2024 (right).
© BRGM
Evolution of the situation observed on piezometers from October 2023 to May 2024.
© BRGM
The groundwater situation
The aquifer situation during the low-water period in 2023 was unsatisfactory, with levels being generally below monthly norms. However, the recharge in 2023-2024 resulted in a significant surplus in almost all the aquifers across the country (with the exception of the Pyrénées-Orientales, Aude and Corsica) which lasted throughout the spring. The state of the reactive aquifers improved considerably at the end of autumn and remained positive until spring, due to several successive recharge episodes. In addition, the overall situation improved gradually in the inertial aquifers.
In May 2024, the situation continued to improve in relation to the previous month. The aquifer situation was generally very satisfactory with most levels above monthly norms: the levels recorded at 19% of the observation points were below monthly norms, 11% were comparable with monthly norms and 70% were above them (compared with 22%, 13% and 65%, respectively, in April).
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 situation was more positive than that observed for the previous year, in May 2023, when 66% of the levels recorded were below monthly norms. Only the aquifers in the Pyrénées-Orientales and Corsica had levels that were lower than in May 2023.
Normally, the recharge in the inertial aquifers in the Artois region, Paris Basin, Sundgau (southern Alsace) and Rhône-Saône corridor ends between April and May, at which point the situations start to stabilise. However, since the recharge continued in May 2024, the situation actually improved in several of the aquifers in the Rhône corridor and in the west and south-west of the Paris Basin. Elsewhere, situations were stable compared with the previous month.
In May 2024, the state of the inertial aquifers was generally satisfactory, with moderately-high to high levels. Locally, less satisfactory levels – from moderately low to low – were recorded on several piezometers in the south-west of the Paris Basin (Normandy chalk aquifer and Cenomanian sand aquifers of Perche and Maine) and in the hilly region of the Drôme (northern part of the Miocene molasse aquifer of the Bas-Dauphiné). Only the most inertial aquifers continued to show moderately-low to low levels: Beauce, Bresse and Dombes, and Sundgau (southern Alsace) regions.
As regards the reactive aquifers, little change was observed compared with April, generally speaking. The only areas in which the situation improved were areas with very reactive aquifers that received a lot of rainfall: from the east of the Languedoc coast to the Armorican Massif, including the centre and west of the Massif Central and the Causses. The situation started to deteriorate slightly in the Alps and in Provence, which were affected by a lack of local rainfall or rain that fell in the form of snow.
The situation was highly satisfactory in most reactive aquifers. The rainfall in April and May kept levels moderately high to very high. The state of the aquifers in the upper valleys of the Pyrénées (Gave de Pau, Adour, upper Garonne and Ariège) was close to normal, due to smaller recharge in 2023-2024 and the absence of inflows from snowmelt. The aquifer levels in Provence and the Côte d'Azur were generally close to normal to moderately high, but even here levels varied, ranging from moderately low to high, depending on local rainfall. In Corsica, strong contrasts were noted in the aquifer situation: low to very low levels in the Cap Corse area and the eastern plains, and close to or above normal monthly levels in the west. Lastly, regarding the aquifers in the Corbières massif and the Roussillon plain, the small recharges at the end of April and beginning of May were unable to compensate for the deficit accumulated over the last two years. The levels remain extremely worrying.
Aquifers that are in a very good state
Several aquifers were found to be in a very good state, with levels being very high in relation to the levels recorded for May in previous years:
- The levels in the reactive bedrock aquifers of the Limousin and Châtaigneraie plateaux, and in the Jurassic and Cretaceous limestone aquifers from the west of the Massif Central to the Armorican Massif were very high, due to a surplus recharge in 2023-2024, which lasted throughout the spring;
- The alluvial aquifers of the downstream Garonne, the Dordogne and their main tributaries are fed by the aquifers mentioned above;
- The aquifers in the bedrock and tertiary formations stretching from the Vilaine basin to the Vendée bocage had a surplus recharge in 2023-2024.
Aquifers in a poor state
Several aquifers were in a poor state, with low to very-low levels compared to those recorded in May of previous years, due to an extreme lack of rainfall over the last few months or years:
- The level of the inertial Plio-Quatenary gravel aquifer of the Sundgau region remained low despite the rainfall in the area. This is due to its highly inertial behaviour;
- The state of the Aude alluvial aquifer improved in May but the level was still low, since the 2023-2024 recharge was insufficient;
- The state of the multi-layer aquifer in Roussillon and the karst limestone aquifers in the Corbières massif remained poor, with low to 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 June, July and August predict drier-than-normal conditions in the south west of the country and on the Mediterranean coast. No particular rainfall scenario has been established for other parts of the country. However, higher than normal temperatures are likely across mainland 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. In June, the aquifer depletion process should commence across the country, or continue in aquifers in which the depletion had already begun, unless there are major rainfall events. However, the majority of aquifers will enter their depletion period in a good state.
Generally speaking, the majority of inertial aquifers (Artois, Paris Basin, Sundgau, Rhône-Saône corridor), will enter their depletion period in June. This will continue until the vegetation becomes dormant and significant rainfall occurs, i.e. until mid-autumn or early winter. These aquifers are not very sensitive to summer drought, due to their high degree of inertia. Rainfall in late spring and summer should therefore have no impact on groundwater levels, unless there are extremely exceptional rainfall events. Levels are therefore expected to fall or remain stable in June and then continue to decrease until the autumn.
The situation in the inertial aquifers should therefore remain stable or deteriorate gradually as of June and through the summer. The seasonal forecasts are quite optimistic for a large proportion of the inertial aquifers: levels should remain close to monthly norms in the aquifers whose levels were above monthly averages at the end of the recharge period. The highly inertial aquifers in the Beauce, Sundgau (southern Alsace), Bresse and Dombes regions were in a less favourable situation in May and will need to be particularly closely monitored. Moreover, water resources could come under pressure in areas in which the levels are currently unsatisfactory, or areas in which the aquifers are greatly used for abstraction (e.g. the Normandy chalk aquifer south of the Seine, the Cenomanian sand aquifers in eastern Pays de la Loire and Centre-Val de Loire, the Miocene molasse aquifer in northern Drôme).
Reactive aquifers are very sensitive to weather conditions. The trends and situations over the coming weeks will therefore depend on total local rainfall, evapotranspiration and the demand on water resources through abstractions. This being said, only occasional, local and low-intensity recharge episodes are likely to occur during the summer. In June, the late snow that fell in the Alps should melt and bring additional water to certain aquifers in the south-east. Groundwater abstraction could accelerate the depletion of these aquifers and affect the situation. Consequently, levels will probably decrease if there is a lack of effective rainfall or if there are significant abstractions. However, they could remain stable or rise if there is enough total rainfall to compensate for outflows to natural outlets (rivers, springs, sea) and abstractions.
The benefits of the abundant recharge in the winter of 2023-2024 should continue to be felt through June and even July in most of the reactive aquifers. Indeed, the overall situation at the end of the recharge period was favourable, suggesting that the summer will be less difficult than last year. This being said, the most reactive aquifers (bedrock aquifers in the Massif Central and Armorican Massif, karst limestone aquifer in Provence, the Jura and around the Massif Central) could empty in just a few weeks, if there is a long, intense drought. Consequently, changes in the levels of these highly reactive aquifers need to be closely monitored, in relation to local rainfall and water abstraction. Finally, certain other areas will also need to be closely monitored, since current levels are not sufficient to guarantee satisfactory levels over the summer: Roussillon, Aude and the northern and eastern parts of 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 7 June 2024, based on data from the ADES database, acquired up to 31 May 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.