Hydrogeological situation on 1 September 2024
In August, the depletion period continued in virtually all aquifers across the country and the levels continued to decrease on the whole (86%). The situation remained highly satisfactory overall, with 70% of aquifer levels above monthly norms. Only the aquifers along the Roussillon coast, in Languedoc and Cap-Corse and on the eastern coast of Corsica recorded levels that were significantly below monthly averages.
In September, the trends will essentially depend on effective local rainfall and the sensitivity of each aquifer. The depletion should continue through to the low water period, which usually occurs between mid-October and November. The levels of the 2024 low-water period should be particularly high over a large part of the country. However, the situation will need to be closely monitored in aquifers that currently have moderately low to very low levels (Roussillon, Languedoc, Eastern and Northern Corsica).
Map of aquifer levels in mainland France on 1 September 2024.
© BRGM
Evolution of the trends observed on piezometers from January to August 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 the replenishment was insufficient. Spring rainfall helped maintain existing groundwater levels and even contributed to replenishing certain aquifers up until May. The depletion continued during the summer, but often at a slower rate due to rainfall and the negligible impact of groundwater abstractions.
In August 2024, depletion remained the dominant trend, with 86% of levels falling (77% in July). This is not surprising given the lack of rainfall over much of the country during the month of August. Moreover, summer rainfall rarely has an effective impact on groundwater recharge, since any water that manages to penetrate into the ground is almost entirely absorbed by vegetation and therefore does not filter down very deeply.
There was depletion in August in reactive aquifers, which are extremely sensitive to a lack of rainfall. Levels decreased, which is the usual trend during the summer. In certain localised areas, the depletion rate was slowed down by the contribution of occasional, local rainfall episodes (for example: the Armorican Massif from Brittany to Vendée, the southern Massif Central from the Cévennes to the Grands Causses, and in Corsica). These rainfall episodes sometimes resulted in a brief recharge of local aquifers, but they were often insufficient to reverse the monthly trends.
As regards inertial aquifers, the water levels have been falling since April in the Artois region and since May or June in the Paris Basin and in the Rhône-Saône corridor. The centre of the Paris Basin benefited from excess rainfall during the spring and summer. The depletion rate remained slow in August, due to the gradual infiltration of the rain that had fallen over recent weeks. As a result, the overall levels remained stable in the chalk aquifers and tertiary formations from the Brie region to the Tardenois region, in Burgundy and in the Gâtinais and Beauce regions.
Comparison between 1 September 2023 and 1 September 2024
Map of France showing the state of the aquifers on 1 September 2023 (left) and 1 September 2024 (right).
© BRGM
Evolution of the situation observed on piezometers from January to August 2024.
© BRGM
The groundwater situation
The 2023-2024 recharge was far above average over a large part of France. At the end of the winter, the aquifer situation was therefore highly satisfactory on the whole. The rainfall in the spring and summer helped to maintain and sometimes even improve the state of the aquifers, with one exception: the recharge was insufficient in the Pyrénées-Orientales, Aude and Corsica and the state of the aquifers remained unsatisfactory.
This situation changed very little between May and August 2024. In August 2024, the groundwater levels were mostly higher than monthly averages: 17% of observation points were below normal and 13% were comparable with monthly norms, whereas 70% were above monthly averages (identical percentages in June and July).
The groundwater situation was much better than that observed last year (August 2023), when 62% of the levels recorded were below monthly norms. Only the groundwater levels observed in the Pyrénées-Orientales and Corsica remained lower than in August 2023. Indeed, in terms of groundwater, August 2024 was the second wettest August on record over the last 30 years (after August 2001, when 83% of levels were above monthly averages).
As regards reactive aquifers, the way in which the groundwater situation evolves over the summer will depend on local cumulative rainfall and the impact of abstractions. Between July and August 2024, there was little change in the situation. It deteriorated slightly across the central strip of the country, from the Périgord and the lower Garonne area to the Saône valley, as well as in the Cotentin and Boulonnais regions. The aquifers in these areas are very sensitive to a lack of effective rainfall in July and August.
In August 2024, the situation remained very satisfactory in the vast majority of reactive aquifers, whose levels were moderately high to very high. This can be explained by a higher-than-normal recharge in 2023-2024 and the significant contribution of rainfall during the spring, as well as occasional episodes of rain in the summer.
Less favourable levels (from close-to-average to low) recorded in certain aquifers were due to a more marked lack of rain. In the Côtes d’Armor, for example, levels were moderately low to low due to the lack of recharge episodes since April. The aquifers in the centre of the Massif Central (Limagne and the Auvergne volcano region) experienced a lower-than-average recharge in 2023-2024. Their situation improved thanks to the spring rains, but then deteriorated again due to the lack of rain in the summer. Low groundwater can be noted along the Chaîne des Puys and in the Forez plain. Finally, groundwater levels in Provence were close to normal overall, although levels varied locally, notably in the Durance plain.
The situation in the aquifers along the Roussillon coast and western Languedoc remained extremely poor. Groundwater levels in the alluvial aquifers of the Aude, Hérault and Orb rivers were low due to a poor winter recharge. On the Roussillon plain and in the Corbières Massif, the state of the aquifers remains very worrying. Levels continued to fall in August, sometimes reaching historic lows, and the situation is still deteriorating. The deep Pliocene aquifer in the Roussillon region managed to remain at a moderately-low level, due to a significant decrease in water abstractions, which enabled local groundwater levels to rise. However, the levels in several other areas remained very low.
Finally, the state of the aquifers in Corsica continued to vary greatly depending on the area. The levels recorded in Cap Corse and the eastern plains were worryingly low, ranging from moderately low to very low. However, on the western coast, they were higher than normal for the month.
As regards the inertial aquifers in the Artois area, Paris Basin, Sundgau (southern Alsace) and Rhône-Saône corridor, the situation has not changed greatly since June. In the south-east of the Paris Basin the levels are unusually stable for the season, and even rising in some areas. This has resulted in an improvement in the state of the Tertiary limestone and sand aquifers from the Brie region to the Tardenois region, and in the Seno-Turonian chalk aquifers in Burgundy and the Gâtinais region.
The state of inertial aquifers remained very satisfactory on the whole, with most levels above monthly norms. The Beauce, Sundgau, Dijonnais, Bresse and Dombes aquifers have very slow reaction times in terms of recharge. Their situation improved significantly during the 2023-2024 recharge period, which was much more plentiful than average, but their levels remain moderately low to close to normal. Still, the situation varied in certain localised areas where levels were less than satisfactory. For example, the Normandy chalk aquifer to the south of the Seine, the aquifers in the north and east of the Beauce region and the Miocene molasse aquifer in northern Drôme still had near-normal to moderately low levels.
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 August in previous years:
- The reactive aquifers in Albian-Neocomian sand and Jurassic limestone formations around the Paris Basin (Lorraine, Côte-des-Bars, Berry, Brenne and north of the Poitou Watershed) benefited from rainfall episodes during the spring and summer;
- The levels in the reactive Jurassic and Cretaceous limestone aquifers around the Aquitaine basin (south of the Poitou Watershed, Charentes, Périgord and Angoulême basin, Causses du Quercy) were strongly boosted by the spring rainfall;
- Some inertial aquifers in the Paris Basin (Sologne and Santerre, Burgundy and Gâtinais regions, Brie and Tardenois regions) and in the Artois region experienced a 2023-2024 recharge that was significantly more plentiful than usual, and which also lasted longer than usual.
Aquifers in a poor state
The state of several aquifers was far from satisfactory, with low to very-low levels compared to those recorded in August 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 levels locally;
- The levels in the alluvial aquifers of the Aude, Hérault and Orb rivers were low due to a poor 2023-2024 recharge;
- The levels of the multi-layer aquifer in Roussillon and the karst limestone aquifer 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 September, October and November predict higher-than-normal temperatures across the country and drier-than-normal conditions in the south. Elsewhere, no clear scenario has emerged for rainfall.
Several low-pressure fronts, accompanied by rain, have been observed and are expected in September. This rain could recharge certain reactive aquifers (particularly alluvial, karst limestone and basement aquifers). In this event, the trend for the month of September in the areas that receive rainfall could see stable and even rising levels. However, this rainfall should have little impact on inertial aquifers in September, since they take a long time to react to such meteorological phenomena.
The depletion in groundwater levels is therefore likely to continue and the recharge episodes should be relatively infrequent and limited, until the vegetation becomes dormant and the episodes of rainfall become more intense and frequent. The low-water period in aquifers usually occurs between mid-October and the end of November.
Any changes in the levels of the aquifers over the coming weeks will depend mainly on the amount of rainfall. Pressure from abstractions of groundwater during the summer should ease towards the end of this period. Over a large part of the country, the levels in August were positive and the overall situation in September should remain better than or close to normal.
As regards the inertial aquifers, in which changes occur very gradually, the situation is unlikely to change much between August and September. Localised shortages could occur in areas where the low-water point is reached later than usual and where the groundwater levels are already below normal, as well as in areas with high abstraction levels (e.g. in the Normandy chalk aquifer south of the Seine, in Beauce, and in the Miocene molasse aquifer in northern Drôme).
The state of reactive aquifers can change quickly. The groundwater situation in these aquifers could remain the same or even improve, at variable rates depending on the total amount of rainfall in a given area. It could also deteriorate if there is a lack of rainfall and in areas where the groundwater is greatly impacted by abstractions.
In southern France, groundwater levels along the Roussillon coast, in Languedoc and in Eastern and Northern Corsica should continue to be closely monitored. The current state of these aquifers ranges from being unsatisfactory to extremely worrying, and the 2024 low-water point is expected to be very severe. The 2024-2025 recharge period will need to be monitored very closely.
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-October 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 10 September 2024, based on data from the ADES database, acquired up to 31 August 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.