Hydrogeological situation on 1 November 2024
The 2024-2025 recharge period began between September and October. In October, with the heavy rainfall and onset of vegetation dormancy, 71% of aquifer levels showed an increase.
A groundwater surplus was observed in October, with 78% of aquifers above monthly norms. The situation nevertheless remains worrying, with very low aquifer levels in the Roussillon region.
In November and during the winter, trends will depend primarily on rainfall. Recharging should continue in areas experiencing rainfall. In the event of insufficient rainfall, depletion could resume, leading to the deterioration of the most reactive aquifers.
Particularly abundant recharging of the water table could have a significant impact on the surface environment, contributing to the overflowing of watercourses or flooding by rising groundwater. The greatest risk in the short term concerns reactive water tables with high to very high levels in October.
Map of aquifer levels in mainland France on 1 November 2024.
© BRGM
Evolution of the trends observed on piezometers from November 2023 to October 2024.
© BRGM
Groundwater trends
The 2024 depletion period was unusual in that it was short and of low intensity. Rainfall in spring and summer helped to maintain water and even replenish some aquifers. In September, the trends differed depending on rainfall and the responsiveness of the aquifers.
In October 2024, the recharge period concerned most aquifers. 71% of the points monitored experienced rising levels (27% in September).
September and October are generally a transitional period for the aquifers. The heavy rainfall and onset of vegetation dormancy enabled the water to filter deep into the ground. This has resulted in a reversal of trends concerning groundwater levels. In recent years, the recharge period has been pushed back as a result of the vegetation remaining active for longer, owing to the mild temperatures and insufficient effective rainfall. In 2024, the conditions for recharge episodes were present from the end of the summer in many areas: wet soils and low temperatures limited evapotranspiration and allowed vegetation to become dormant. The winter recharge therefore began a little early, as early as September in areas experiencing rainfall and with reactive water tables, and more widely in October.
In October 2024, rising water levels were observed in most aquifers. Stable or falling levels can be seen in more inertial aquifers and areas with insufficient effective rainfall. For example, the levels in the chalk aquifers of the Artois-Picardy, Picard Plateau and Normandy regions stabilised in October, following slow infiltration of the effective rainfall in September. In the Adour-Garonne region, recharging is more difficult in the less reactive aquifers of the upstream Garonne and the Oligocene limestone aquifers of the Entre-deux-Mers region, where levels are stable or still falling. Last, the reactive water tables are responding to the lack of rainfall in October. Levels are stable in the Jurassic and Cretaceous limestone water tables in the Côte-des-Bars region, from the Bessin to the Sarthe, in the Périgord and Angoulême basin, and in the alluvial and tertiary aquifers of the Bas-Rhône, Vistrenque and Roussillon regions.
Comparison between 1 November 2023 and 1 November 2024
Map of France showing the state of the aquifers on 1 November 2023 (left) and 1 November 2024 (right).
© BRGM
Evolution of the situation observed on piezometers from November 2023 to October 2024.
© BRGM
The groundwater situation
Groundwater levels remained above monthly norms overall, during the 2024 depletion period. This can be explained by a higher-than-normal recharge in 2023-2024 and the significant contribution of effective rainfall during the spring, as well as occasional episodes of rain over the summer. The only exceptions were the Pyrénées-Orientales, Aude, Cap Corse and the plains of eastern Corsica, where groundwater levels remain low after insufficient recharging in 2023-2024 and little or no rainfall during the spring and summer of 2024.
In October 2024, a surplus was observed in groundwater levels across much of the country: 12% of observation points were below monthly norms, 10% were comparable and 78% were above monthly norms, compared with 17%, 10% and 73%, respectively, in September 2024. Between September and October 2024, the situation improved or remained stable for all aquifers.
The situation is much improved on a year ago, in October 2023, when 65% of the levels observed were below monthly norms. Pyrénées-Orientales is the only area where aquifer levels are lower than in 2023. October 2024 was the second wettest October on record over the last 30 years, after October 2001, when 83% of aquifer levels were above the norm for that month.
The very high levels in October mainly concerned the reactive basement aquifers in the south of the Armorican Massif and the Massif Central, the Triassic sandstone aquifers of Lorraine, the Cretaceous and Jurassic limestone aquifers of the Jura, the area around the Paris Basin and the Aquitaine Basin, the plioquaternary formations of the Aquitaine Basin and the large alluvial plains of the Saône, the upper Rhône, the Garonne, the Adour and their main tributaries. Record low-water levels are observed from time to time. As a result, local levels are seeing lows that usually occur only once in twenty years in the Tertiary limestone and sand aquifers in the Brie Tardenois region, the Jurassic limestone aquifers in the Berry and around the Aquitaine Basin, the alluvial aquifers of the Garonne and Dordogne rivers and their main tributaries, the plioquaternary formation aquifer of the Aquitaine Basin and the basement aquifers of the Limousin plateau.
Concerning reactive water tables, high to moderately high levels were observed in areas experiencing insufficient rainfall in October, such as the Jurassic limestone aquifers in Lorraine and the Cévennes region, the basement aquifers in Brittany and from the Cotentin region to the Mayenne, the Auvergne volcano aquifers and the alluvial and karstified limestone aquifers of the Bas-Rhône and Provence regions.
In the inertial aquifers of the Artois-Picardy region, the Paris Basin and the Rhône-Saône corridor, the situation has gradually improved over the past hydrological year. Levels were comparable overall to normal-to-high monthly figures. Less favourable levels, with normal to moderately low figures, can still be observed locally in some areas of the central-west Paris basin (Normandy chalk and Beauce), Bresse and Dombes and Bas-Dauphiné (Miocene molasse). Levels remain moderately low for the Sundgau aquifer, owing to its very high inertia.
In the south, the situation remained sensitive over part of the summer for several aquifers along the Languedoc coast, Cap Corse and the plains of eastern Corsica. Rainfall in September and October improved the condition of the aquifers concerned. In October, levels ranged overall from moderately low to moderately high. However, some areas of the Languedoc region remain sensitive locally with piezometers still showing low to very low levels: upstream Aude, Orb, the sand aquifers of Valras-Agde, and the Vistrenque region.
Last, water levels remain very low in the aquifers of the Roussillon plain and the Corbières Massif. The rain seen in recent weeks has not been sufficient to compensate for the lack of rainfall accumulated over the past two years. Some levels are still at historic lows.
Aquifers that are in a very good state
Many aquifers are showing a surplus with high to very high levels, compared to the levels recorded for October in previous years:
- The inertial to slightly reactive aquifers of the chalk and tertiary formations in Artois-Picardy, Champagne, Burgundy and the Gâtinais, Touraine, Sologne and Sancerre, and the Brie Tardenois region;
- The reactive aquifers around the Paris Basin, in Lorraine and Alsace, the Jura, the Massif Central, the Armorican Massif and the Aquitaine Basin received significant rainfall in spring and summer rainfall with further inflows in September and October.
Aquifers in a poor state
The situation was unfavourable in several aquifers with moderately low to very low figures compared to the levels recorded for October in previous years:
- The Sundgau aquifer (southern Alsace) is changing very slowly, owing to its significant inertia, with overall levels remaining moderately low;
- The situation remains sensitive locally with very low levels upstream of the Aude alluvial aquifer and moderately low to low levels for the Orb alluvial aquifer, the non-coastal part of the Valas-Agde Astian sands aquifer and the Vistrenque aquifer;
- Water levels in the multi-layer aquifers in the Roussillon region and the karst limestone aquifers of the Corbières Massif remain very low, owing to a severe lack of rainfall over the past 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 November and December 2024 and January 2025 indicate higher than usual temperatures across the whole of France. No clear scenario has emerged for rainfall.
Vegetation became dormant in October, the soil is damp and the recharge period has begun. The conditions were right for recharging to continue in November. The trends over the next few weeks will depend exclusively on the level of rainfall infiltration and therefore the rainfall totals, and the inertia of the aquifers.
In the event of sufficient total rainfall in November, this effective rainfall should result in recharge episodes. The impact of the rain should quickly be visible on reactive aquifers and more slowly and gradually on inertial aquifers. In cases where surpluses are already observed, levels could remain high to very high. The least favourable situations should then start to improve, particularly where there is a high level of total rainfall infiltration and where the aquifer is reactive. A number of low-pressure fronts, accompanied by heavy rain, were observed in late October and early November and are still expected in southern France, particularly the Mediterranean coastal area. Intense episodes are not conducive to optimum rainfall infiltration and thus recharging of the aquifers. Nevertheless, total effective rainfall could be sufficient to compensate for local deficits in the Languedoc region.
In the event of insufficient rainfall in November, the most reactive water tables could be depleted again, and the situation could then deteriorate. Concerning inertial aquifers, the recharge is likely to slow initially and then cease if the lack of rainfall continues over several weeks.
In the longer term, forecasts clearly indicate that areas where groundwater levels are currently above monthly norms will not experience a winter drought. Groundwater levels in reactive aquifers in early spring 2025 remain uncertain, and will depend on the overall recharge observed in autumn and winter. Note that spring rains will also be essential to delay the start of the depletion period. Concerning inertial aquifers, given the satisfactory low-water level and an early start to the recharge period, levels in spring 2025 will probably be satisfactory, close to or above the norms. Last, forecasts for the aquifers in the Roussillon region are not very optimistic for the coming months. The 2024-2025 recharge period will need to be particularly long and abundant to replenish reserves over the long term.
Given the high to very high levels observed in October and the early start to the recharge period, a particularly plentiful recharge could have a significant impact on surface environments.
The short-term risk of flooding from rising groundwater concerns reactive water tables. These aquifers can play a direct role by overflowing or contributing to the recharge of watercourses that are already flooding. More often than not, however, they play an indirect role: when the soil and subsoil are saturated, aquifers can aggravate the run-off or overflow of water courses by limiting the infiltration of rain and the evacuation of water. Particularly close attention should be given to reactive aquifers, which reached very high levels in October and could soon reach or remain at historically high levels, particularly in areas prone to flooding as a result of rising water tables:
- Basement aquifers of the Armorican Massif in Brittany and the Pays-de-la-Loire region;
- Massif Central basement aquifers in the Limousin region;
- Jurassic limestone aquifers in the Berry and Brenne (Centre-Val-de-Loire), the Poitou watershed and the Charentes region;
- Plioquaternary formation aquifer in the Gironde region;
- Alluvial aquifer of the downstream Garonne and downstream Dordogne rivers in the Gironde region.
Concerning the more inertial aquifers, the risk of flooding by rising groundwater is still largely uncertain overall, as it depends on the total rainfall received by the aquifer over the entire 2024-2025 recharge period. Changes in inertial aquifer levels will therefore need to be monitored particularly closely during the autumn and winter, with a greater risk in the spring of 2025. However, less inertial water tables in the Paris Basin saw high to very high levels in October and could reach historically high levels as early as November or December. Increased surveillance is recommended in these areas over the coming weeks:
- Semi-inertial Turonian chalk marl aquifer in the Champagne region;
- Semi-inertial Tertiary limestone and sand aquifer in the Brie Tardenois region.
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-December 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 7 November 2024, based on data from the ADES database, acquired up to 31 October 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.