The hydrogeological situation on 1 February 2025
In January 2025, groundwater recharge continued, with 71% of observation points showing an increase in levels. As a result of excess rainfall across the northern two-thirds of France, the south-west and Corsica, the situation remained stable or improved, with high groundwater levels.
In the south-east, aquifers are suffering from a lack of rainfall, with levels below the monthly norms. Groundwater levels in the Roussillon region remain low to very low.
With winter coming to an end, future trends and developments will depend primarily on the amount of rainfall. In view of the winter recharge, satisfactory levels can be expected across much of the country as we move towards the spring. However, forecasts remain uncertain for reactive aquifers, as they depend on rainfall in late winter and early spring.
Carte de France hexagonale de la situation des nappes d'eau souterraine au 1er février 2025.
© BRGM
Evolution of the trends observed on piezometers from February 2024 to January 2025.
© BRGM
Trends
In rainy parts of the country with reactive aquifers, the winter recharge period began in September 2024, extending to virtually all aquifers in October. Overall, the recharge was extremely dynamic in October, but slowed significantly in November. It then picked up again from December, except in the south-east.
In January 2025, the recharge continued, with 71% of levels showing an increase (67% in December).
Across the northern two-thirds and south-west, the levels of reactive aquifers generally increased. Two recharge episodes were observed at the beginning and end of the month. These recharge episodes were particularly abundant in the aquifers of the Armorican Massif basement. Water levels remained stable in areas experiencing less rainfall: the Jurassic limestone aquifers in the Côte-des-Bars and Berry regions and the Limagne aquifer. The inertial aquifers of the Paris Basin, Sundgau (southern Alsace) and the Saône corridor are continuing to recharge. The inertia of these aquifers means that it takes several weeks for rainfall to seep down through the unsaturated zone.
The aquifers in the south-east have not received sufficient accumulated rainfall over the last three months. Levels are therefore down or stable overall. This applies equally to the inertial groundwater in the Rhône corridor, from the east of Lyon to the Bas-Dauphiné, and the reactive aquifers in the south of the Massif Central and around the Mediterranean. A rise in aquifer levels can be seen only in the Roussillon area. In Corsica, following surplus rainfall in mid-January, aquifer levels rose across the eastern and south-western coastal plains, while remaining stable across Cap Corse and the north-west.
Comparison between 1 February 2024 and 1 February 2025
Map of France showing the state of the aquifers on 1 February 2024 (left) and 1 February 2025 (right).
© BRGM
Evolution of the situation observed on piezometers from February 2024 to January 2025.
© BRGM
Aquifer situation
The recharge period began between September and October, reaching particularly high levels. Although levels deteriorated slightly in November and December 2024 , they nevertheless remained above normal. Only the aquifers in the Roussillon region and locally in the south-east and Corsica showed very low levels.
In January 2025, aquifer levels began to rise again, continuing to show a surplus: The levels recorded at 18% of the observation points were below monthly norms; 14% were comparable and 68% were higher (compared with 17%, 22% and 61% respectively in December 2024). Note that 16% of the points monitored reached very high levels in January (14% in December).
The situation was slightly better than last year, in January 2024, when 56% of the levels observed were above monthly norms. For most aquifers, levels are higher than in 2024. This is particularly true of the inertial aquifers, whose condition has gradually improved over the last 12 months.
Concerning this type of aquifer, levels in the Paris Basin and Artois Basin are high to very high upstream (east and south) and moderately high downstream (west). A few piezometers are still recording moderately low to near-normal levels in the highly inertial Normandy Chalk and Beauce aquifers. Aquifers in the Sundgau (southern Alsace) and Saône corridor have remained moderately low with levels comparable to normal since the summer of 2024, owing to their considerable inertia. However, local situations can vary greatly. Concerning the inertial water tables in the Rhône corridor, levels are more satisfactory upstream (eastern Lyon and Savoyard foothills) and moderately low downstream (Bas-Dauphiné), owing to varying levels of rainfall in recent months.
In the reactive aquifers of the northern two-thirds and south-west, the situation has not changed since December, although levels are rising across the Armorican Massif and western Massif Central owing to very high rainfall. These aquifers are showing a surplus, with levels moderately high to very high overall that remain comparable to norms in the centre of the Massif Central (Limagne and volcanoes), since in these areas they are less reactive. The reactive aquifers in the basement formations of the south-eastern Armorican Massif have remained with very high levels since May 2024; These aquifers may have contributed to the flooding observed in January in Brittany, either directly by overflowing or feeding into rivers already at flood level, or indirectly by limiting the infiltration of rainfall and water run-off.
In the south-east, the impact of the lack of rainfall over the last three months can be clearly seen. The situation here is less satisfactory, with levels varying between moderately low and close to normal. However, local situations can vary greatly. Levels are above normal in the upstream (northern) areas of the Massif Central basement and limestone aquifers, but moderately low to low in the south (around the Cévennes and Montagne Noire). Some local situations remain sensitive, with low levels across the Provence aquifers and the upstream part of the Astien aquifer at Valras-Agde.
Levels in the aquifers of the Roussillon plain and Corbières Massif remain low to very low. The rainfall of recent months has failed to compensate for the accumulated lack of rainfall over almost three years in the Pyrénées-Orientales département.
Last, excess rainfall in January helped recharge the aquifers in Corsica. The contrast between western and eastern Corsica is diminishing. Nevertheless, levels remain low to very low in a few spots on the Tarco and Fium'Orbu coastal plains.
Aquifers with surplus water
Several aquifers showed surplus levels, with high to very high levels, compared to those recorded for January in previous years:
- The state of the mixed to inertial aquifers upstream (east and south) of the Paris Basin continues to improve slowly with levels that are high to very high;
- The reactive aquifers in the basement formations of the south-eastern Armorican Massif receive frequent rainfall and have remained at very high levels since May 2024;
- Levels are very high in the reactive aquifers of the Combraille basement and Millevaches plateau and in the Jurassic limestone formations from the Poitou region to La Brenne and Le Berry.
Aquifers with low water levels
The situation was unfavourable in several aquifers with moderately low to very low levels compared to those recorded for January in previous years:
- Concerning the aquifers along the Mediterranean coastline, from Languedoc to Provence, levels remain moderately low to very low locally, after three months of insufficient rainfall.
- Levels in the karst limestone formations of the Corbières Massif are rising but remain low;
- The situation of the aquifers in the Roussillon multilayer formation remains critical, with low to very low levels, despite stable or rising levels.
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 the months of February, March and April 2025, predict higher-than-normal temperatures across the country and drier-than-normal conditions in the south of France and Corsica. No clear scenario has emerged concerning rainfall across northern France.
With regard to inertial aquifers, winter rainfall should continue to infiltrate slowly, bringing about a gradual improvement in the situation. The state of the aquifers should then stabilise or gradually improve in February.
With regard to reactive aquifers, the rainfall of late January and early February, particularly in the south-east, should lead to a recharge episode. In the event of significant accumulated rainfall, the most reactive aquifers (basement, karst limestone, alluvial) could experience sharp rises in water levels. The Languedoc and Provence regions have seen particularly high levels of rainfall and the groundwater situation is expected to improve in early February. If rainfall is insufficient during the rest of the month, however, the recharge process is likely to slow in the reactive aquifers concerned and the situation could then deteriorate more or less rapidly.
In the longer term with the period through to spring and the regrowth of vegetation, trends and changes in the aquifer situation will depend on rainwater infiltration, and hence total rainfall, as well as the reaction time of the aquifers (reactive/inertial). Nevertheless, forecasts continue to indicate that virtually all the areas around the country in which groundwater levels are currently above monthly norms are unlikely to be affected by a winter drought.
The situation of the inertial aquifers in the Artois region, Paris Basin, Sundgau (southern Alsace) and Rhône-Saône corridor should continue to improve slowly or remain stable over the coming weeks. The levels in spring 2025 will probably be satisfactory, close to or above the seasonal norms. Forecasts are more uncertain for the Bas-Dauphiné aquifer. If seasonal forecasts from Météo-France are confirmed, levels could remain moderately low or even deteriorate, or – in contrast – rise to levels close to seasonal norms in the event of excess rainfall.
Concerning the reactive aquifers, the start of the winter recharge indicates satisfactory levels at the end of the winter in much of northern and south-western France. In the south-east, levels could return to above-normal levels, in the event of well-distributed rainfall episodes over the coming months. Melting snow could also recharge some water tables. Nevertheless, the situation in reactive aquifers can change rapidly and forecasts will remain uncertain through to the end of the winter. Groundwater levels in the summer of 2025 will depend on an abundant winter recharge continuing into the spring. This would push back the start of the depletion period. Last, sustainable replenishment of aquifers in the Roussillon plain appears unlikely over the next few months. Levels are expected to remain below normal until spring, and even low to very low for the deep Pliocene sands aquifer.
The short-term risk of flooding from rising groundwater levels appears to be receding in the case of reactive aquifers. It cannot be neglected entirely, however, as it depends on recent rainfall. Concerning the inertial aquifers of the Artois Basin and Paris Basin, this type of risk remains possible in late winter and early spring, if total rainfall totals over the next few months is higher than average. However, current overall levels are below those of January 2001. Water levels in the semi-inertial Tertiary limestone and sand aquifer in the Brie Tardenois region were very high in January and could reach historically high levels by the end of the winter. Close monitoring is recommended in these areas over the coming weeks.
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-March 2025.
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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Carte établie le 7 février 2025 par le BRGM, à partir de données de la banque ADES acquises jusqu’au 31 janvier 2025.
Source des données : banque ADES (ades.eaufrance.fr) / Hydroportail (hydro.eaufrance.fr) / Fond de carte © IGN. Producteurs de données et contribution : 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).
Cette carte présente les indicateurs globaux traduisant les fluctuations moyennes des nappes. Ils sont établis à partir des indicateurs ponctuels relevés au niveau des points de surveillance du niveau des nappes (piézomètres).
L'indicateur "Niveau des nappes" compare le mois en cours par rapport aux mêmes mois de l’ensemble de la chronique, soit au minimum 15 ans de données, et jusqu'à plus de 100 ans. Il est réparti en 7 classes, du niveau le plus bas (en rouge) au niveau le plus haut (en bleu foncé).
Les zones grises correspondent à des secteurs sans nappes libres, c'est-à-dire avec une couche imperméable ou semi-perméable au-dessus de la nappe, et/ou des secteurs comportant une très faible densité de points de suivi. Ce dernier cas concerne notamment les zones montagneuses dont les nappes sont petites et hétérogènes.
L'indicateur "Évolution des niveaux" traduit la variation du niveau d'eau du mois échu par rapport aux deux mois précédents (stable, à la hausse ou à la baisse).
Ces indicateurs globaux rendent compte de situations et de tendances générales et ne tiennent pas compte d'éventuelles disparités locales.