Hydrogeological situation on 1 August 2024
In July, the seasonal decline in groundwater levels is under way at most observation points. Summer rainfall has had very little impact on groundwater levels.
The state of groundwater storage in July was very satisfactory, following a 2023–2024 recharge surplus and a strong contribution from spring rainfall. However, groundwater levels were recorded as below average along the Roussillon coastline and in Languedoc, Corsica and southern Alsace.
In August, groundwater levels are expected to continue declining. The storms that usually occur towards the end of summer are expected to have an impact only for the most reactive aquifers. The state of groundwater storage is expected to remain satisfactory over much of the country, with levels above or close to monthly averages. However, the situation should be closely monitored where groundwater observation points currently show moderately low to very low levels, as well as in areas where abstraction demand is particularly high.
Map of aquifer levels in mainland France on 1 August 2024.
© BRGM
Evolution of the trends observed on piezometers from December 2023 to July 2024.
© BRGM
Groundwater trends
During the autumn and winter of 2023–2024, most of France experienced substantial groundwater recharge, except in the Pyrenees and Roussillon, along the western coastline of Languedoc and in Corsica, where replenishment was inadequate. Spring rainfall helped to keep levels up, even resulting in replenishment of groundwater up until May. Groundwater levels have been falling since June, but often at a slower rate.
The seasonal decline in groundwater levels continued during July 2024. Levels rose at only 10% of observation points and fell at 77% (compared to 20% for higher levels and 62% for lower levels respectively in June). This is usual for this time of year. In general, summer rainfall infiltrates poorly at depth. It is absorbed by the soil and primarily benefits vegetation. The seasonal groundwater decline predominated at all observation points in July.
This decline was observed in July at almost all observation points for reactive groundwater bodies, which are easily affected by drought. However, the rate of decline was sometimes reduced by small rainfall events generating a temporary recharge to groundwater. Rising or stable groundwater levels resulting from intense rainfall events were observed in northern France in the Lorraine Triassic limestone formations and the Jurassic limestone formations of the southern and southeastern edge of the Paris Basin (Cote-des-Bars, Berry and Brenne), in the southern Massif Central basement, in the lower Rhône and Durance alluvial and tertiary formations and in the karst limestone of the Corbières massif.
The seasonal decline of levels in less reactive aquifers began slowly in April in the Artois Basin and between May and June in the Paris Basin and the Rhône-Saône corridor. Groundwater decline was well under way in July, with water levels falling in most areas. Less reactive aquifers in Beauce, Sundgau (southern Alsace) and Bresse-Dombes showed a much slower response to spring precipitation, which reached groundwater several weeks after infiltration. In July, the groundwater trend continued to reverse, and the water level decline set in gradually.
Comparison between 1 August 2023 and 1 August 2024
Map of France showing the state of the aquifers on 1 August 2023 (left) and 1 August 2024 (right).
© BRGM
Evolution of the situation observed on piezometers from December 2023 to July 2024.
© BRGM
The groundwater situation
Rainfall events during the winter of 2023–2024 and spring of 2024 led to a considerable improvement in groundwater levels. In recent months, the overall situation has been very satisfactory. One exception, however, was the shortfall in groundwater recharge and poor state of groundwater levels in Pyrénées-Orientales, Aude and Corsica in 2024.
In July 2024, groundwater levels were close to those of May and June. They were above monthly norms at most observation points: the levels recorded at 17% of the observation points were below monthly averages, 13% were comparable with monthly norms and 70% were above average (same percentages as in June).
Groundwater levels were better than those observed for the previous year, in July 2023, when 72% of the levels recorded were below monthly norms. Only the groundwater levels observed in the Pyrénées-Orientales and Corsica remained lower than in July 2023. July 2024 was the second wettest July recorded for groundwater over the last 30 years (after July 2001 and just before July 2013).
Where aquifers are typically more reactive, how groundwater levels change over the summer will depend on local cumulative precipitation and abstraction pressure. Groundwater levels changed very little between June and July. They improved slightly in areas where it rained around the southeastern edge of the Paris Basin and in the eastern Massif Central.
The situation remained very satisfactory where aquifers are reactive, with many levels recorded as moderately high to very high. This can be explained by a surplus recharge in 2023–2024 and a strong contribution from spring rainfall. However, the lack of rainfall in July had a local impact on certain areas. In the Côtes d’Armor, for example, levels were moderately low to low due to the lack of recharge events since April. In the Pyrenees and central Massif Central, there was a shortfall in recharge, and levels close to normal to moderately low still occurred in the upper valleys of the Adour, Gave de Pau and Garonne rivers as well as in the volcanic formations of the Massif Central. Lastly, groundwater levels in Provence were close to normal overall but varied significantly depending on local cumulative spring precipitation.
The situation remained less than adequate along the western coastline of Languedoc and in Roussillon. Groundwater levels in alluvial formations of the Aude, Hérault and Orb rivers were low due to poor winter recharge. In the Valras-Agde Astian sands, they were moderately high, mainly due to low abstraction pressure for drinking water, tourism and irrigation. In the Roussillon plain and the Corbières massif, rainfall over the last few months was not enough to cover the shortfall in recharge of the last two years. Groundwater levels deep below the surface in the Roussillon Pliocene formation were observed to be moderately low in July. However, many groundwater observation points in this area were still showing very low levels. This can be explained by a recovery of groundwater levels locally, due to significantly reduced abstraction pressure.
Finally, in Corsica, groundwater levels varied widely, from moderately low to very low in the Cap Corse area and the eastern plains, to close to normal to very high along the western coastline.
For the less reactive aquifers of the Artois Basin, Paris Basin, Sundgau (southern Alsace) and Rhône-Saône corridor, groundwater levels stayed the same between June and July, and even continued to improve for the least reactive of them.
Levels were generally very satisfactory, from moderately high to high. At highly unreactive observation points in Beauce, Bresse-Dombes and Sundgau (southern Alsace), levels were recorded as moderately low to close to normal.
There were local variations, and some water levels were less than adequate. In the northern Drôme for example, the central-western and southwestern part of the Paris Basin (in the limestone formations south of the Seine, northern Beauce and the Cenomanian sands of Sarthe), water levels were observed to be close to normal to moderately low.
Aquifers that are in a very good state
Observation points indicated a very good state of groundwater storage, with very high water levels compared to the levels recorded for July in previous years:
- The more reactive groundwater bodies in Jurassic limestone formations around the Paris Basin (Cote-des-Bars, Berry, Brenne and north of the Poitou watershed) showed a positive response to rainfall events in July;
- Groundwater levels in the reactive Jurassic and Cretaceous limestone formations in the northern Aquitaine Basin (south of the Poitou threshold, Périgord and Angoulême Basin) were strongly boosted by spring rainfall;
- Groundwater levels in the basement of the Vilaine Basin in the Vendée bocage region benefited from significant effective rainfall during the winter and spring.
Aquifers in a poor state
Several observation points showed less than adequate states with low to very-low levels compared to those recorded in July of previous years, due to an extreme lack of rainfall over the last few months or years:
- The state of aquifers in Cap Corse and the eastern plains of Corsica remained poor, with moderately low to very low groundwater levels locally;
- Observation points in the alluvial formations of the Aude, Hérault and Orb rivers showed low groundwater levels;
- Groundwater levels in the multi-layer aquifer in Roussillon and the karst limestone of the Corbières massif remained poor, with very low levels, due to a lack of rainfall for more than 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 August, September and October predict higher-than-normal temperatures across the country and drier-than-normal conditions in the southern third of the country. Elsewhere, no clear scenario has emerged for rainfall.
Summer precipitation does not usually lead to aquifer recharge. The water that seeps into the ground is usually taken up by vegetation and, furthermore, summer storms result in more run-off and less effective rainwater infiltration. The lack of rainfall and high temperatures could also lead to agricultural drought and could increase the water requirements of vegetation and abstraction. As a result, the situation is likely to deteriorate fast, particularly for reactive groundwater bodies that are heavily used.
Reactive aquifers, particularly alluvial, basement and karst formations, are sensitive to weather conditions. Trends and changes in groundwater levels in August will mainly depend on effective local precipitation and on the level of water use. Therefore, the lack of effective rainfall combined with significant abstraction will cause the seasonal decline in groundwater levels to persist. This situation could deteriorate further without the contribution of precipitation. In areas receiving rainfall and where groundwater levels respond quickly to precipitation, periods of recharge are expected to occur. However, rainfall infiltration at depth is likely to remain localised and not very intense until the autumn.
Over much of the country, July groundwater levels were good. Levels in August are expected to remain close to normal levels. However, the situation could worsen rapidly, with levels below normal in August in areas affected by intense drought or significant abstraction, in connection with high temperatures. Caution is therefore required, especially where groundwater bodies are very reactive to these changes.
In southern France, groundwater levels along the Roussillon coastline, in Languedoc and in Corsica should continue to be closely monitored. The state of groundwater in these areas is a cause for minor to serious concern, and levels are expected to decline further in the next few weeks if no precipitation occurs and if summer abstraction persists at current high levels in some areas.
In the Artois Basin, Paris Basin and the Rhône-Saône corridor, where groundwater bodies have a delayed response to precipitation, the seasonal decline is expected to continue until vegetation becomes dormant and abundant precipitation occurs. Levels are therefore expected to keep falling until mid-autumn and the beginning of winter, barring exceptional rainfall events.
Groundwater levels are expected to stay the same or decline very gradually. The rate at which this occurs will mainly depend on the volume of groundwater abstraction, and areas with heavy water use could see a more rapid worsening of the state of groundwater. The situation in August should generally remain similar to that in July, with moderately low to high levels. Local shortages could occur in areas where water levels are currently below normal, or in areas with high abstraction levels (e.g. in the Normandy chalk formations south of the Seine, the Cenomanian sands of the south-western part of the Paris Basin, in northern Beauce, and in the Miocene molasse formation in northern Drôme).
Next groundwater tables status report
Our groundwater report is now published every month, in the middle of the month.
The next issue will be published in mid-September 2024.
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.
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Map drawn up by BRGM on 8 August 2024, based on data from the ADES database, acquired up to 31 July 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.