Aquifers: assessment of changes in groundwater levels in 2024-2025

Situation at the start of the hydrological year

Low-water period 2024 (start of recharge period)

The 2024 lowest-water levels mark the beginning of the 2024-2025 hydrological year. They occurred slightly earlier throughout the country, generally between September and October 2024.

The first recharge events were observed locally in the reactive aquifers during the second half of August and at the beginning of September 2024 with the late summer storms. This effective rainfall temporarily recharged many reactive aquifers, thus slowing the rate of discharge. The 2024 low-water levels for reactive aquifers were recorded during the first half of September over a large part of the southern half of the country and Corsica, and between the end of September and October over the northern half as well as Roussillon, Languedoc and the southern Massif Central.

The 2024 low-water levels for inertial aquifers generally occurred between late September and mid-October. The low-water period arrived later, between mid-November and early December, at some of the more inertial observation points in the Artois Basin and the Paris Basin.

Aquifer situation at the beginning of the recharge period

Aquifer levels were generally higher than usual during the 2024 low-water period. In fact, the 2023-2024 recharge was generally well above normal, and the 2024 discharge was atypical, with strong support from rainfall infiltrated during the spring and, to a lesser extent, the summer. In addition, the abstraction demand was probably low, due to the low temperatures.

For the inertial aquifers of Artois-Picardie, Paris Basin and the Rhône-Saône corridor, low-water levels in 2024 were generally moderately high to high. They reached very high levels in the Artois-Picardy basin, in Champagne, Brie and Tardenois, in Burgundy and Gâtinais and in Sologne and Sancerre. There were still levels comparable to normal to moderately low in the Beauce, Bresse and Dombes and Sundgau aquifers, as a result of their very high inertia.

The reactive aquifers in the northern two-thirds and south-west of the country had higher levels than usual, with low-water levels being generally high to very high. The very high levels during the low-water period mainly concerned the highly reactive Jurassic and Cretaceous limestone aquifers (Boulonnais, Lorraine, Jura, around the Paris Basin and around the Aquitaine Basin), but also the Vosges sandstone aquifers in Lorraine, the basement aquifers in the south of the Armorican Massif, the Plioquaternary formations in the Aquitaine Basin and the alluvial aquifers in the Alpine valleys. Some aquifers that were less reactive or that had been less sustained during the spring and summer of 2024 showed moderately high levels during the low-water period: north-west of the Armorican massif, Avesnois, Limagne plain, volcanoes of the Massif Central and southern plain of Alsace.

Record low-water levels were recorded in several reactive aquifers and in the inertial aquifer in the Tertiary limestone and sand formations of the Brie and Tardenois regions. A short-term risk of flooding due to rising water tables was identified for reactive aquifers. These reactive aquifers can play a direct role by overflowing or discharging into watercourses that are already at full capacity. More often than not, however, they play an indirect role: when the ground and subsurface are saturated, aquifers can aggravate the run-off or overflow of water courses by limiting the infiltration of rain and the evacuation of water.

Around the Mediterranean and Corsica, levels during the low-water period in 2024 were less favourable, ranging from low to moderately high. There was insufficient recharge in 2023-2024 and the aquifers received little support from rainfall in the spring and summer of 2024. Low-water levels in 2024 were again particularly intense, reaching historic lows, in the aquifers of the Roussillon plain, the limestone formations of the Corbières massif and the alluvial deposits of the Aude valley. Cumulative rainfall infiltration during the 2023-2024 hydrological year was far from enough to offset the cumulative rainfall deficit of the previous two hydrological years. It should be noted that the deep Roussillon Pliocene aquifer appeared to be only moderately low in some areas as a result of the sharp reduction in demand for water abstraction, leading to a local rise in levels. In Corsica, the state of the aquifers was very mixed, with worryingly low levels, from moderately low to very low, on Cap Corse and the eastern plains, and levels above monthly averages on the western coast.

Analysis of the 2025 low-water period

Generally speaking, the summer drop in levels is linked to low rainfall, high evapotranspiration and/or vegetation growth, as well as greater demands on groundwater in certain areas (pumping). Generally, from mid-April until autumn, water seeping into the soil is usually completely taken up by vegetation. In this case, drought or rainfall have little effect on groundwater levels. An improved groundwater situation with higher groundwater levels will require significant rainfall, damp soil and vegetation that is more or less dormant. Abundant rainfall can only have an observable effect on the more reactive aquifers, resulting in a slowdown in groundwater discharge or even an increase in levels, which is often temporary. These occasional inflows have a beneficial effect, as they postpone the start of the discharge period to spring and sustain groundwater levels in summer. During the discharge period, the fall in levels can occur much more rapidly in areas where there is heavy demand (abstraction) on groundwater resources.

At the end of the discharge period, aquifers reach their lowest level of the year, known as the “low-water period”. The heavy rainfall and onset of vegetation dormancy enable the water to filter deep into the ground. This results in a reversal of the trend for aquifer levels. These low-water levels are generally observed from October to November, and until December for the most inertial aquifers. But they can occur earlier in reactive aquifers, from the end of August or during September, with the end-of-summer storms that mark the start of recharge.

Aquifer discharge trends

As regards the inertial aquifers, their state deteriorated gradually from the 2025 high-water period, i.e. generally March-April for the Artois Basin, the Paris Basin and the Sundgau (southern Alsace) and April-May for the Rhône-Saône corridor. The situation deteriorated more quickly in the less inertial aquifers of the Artois coast and the eastern edge of the Paris Basin, which were more sensitive to the end of the deficient recharge period. Normally, the discharge of inertial aquifers continues uninterrupted until autumn, when vegetation becomes dormant and the first significant rainfall occurs. Rainfall in spring and summer has little impact on these aquifers. However, abstractions for irrigation were often lower in August 2025 than in previous years. Two factors may explain the early cessation or reduction of these abstractions. On the one hand, there was enough rainfall to cover part of the plants' water requirements. On the other hand, the crops developed early this year, leading to early harvests and therefore less demand for irrigation. A slower-than-usual rate of discharge was observed in heavily used aquifers, such as the Beauce aquifer.

The 2025 discharge period did not set in at the same time for all the reactive aquifers. Discharge began very early, in February 2025, in the northern two-thirds and south-west of the country. It remained very intense during the spring of 2025 for the reactive aquifers in the northern half and centre-east of the country. For the south-western aquifers, recharge events were recorded at the end of April and in May 2025, following excess rainfall or contributions from melting snow. For the aquifers in the south-east and Corsica, the discharge period began late, between April and May 2025. From May onwards, levels continued to fall in all reactive aquifers, as rainfall was no longer effective in generating recharge episodes. Increased demand on groundwater (abstraction for irrigation and tourism) began to be felt locally. However, the stormy spells that occurred during the summer of 2025 reduced the rate at which certain highly reactive water tables were discharged: the north-east in June, the northern half of France, the Mediterranean region and Corsica in July, and the southern two-thirds of France in August. In August 2025, the discharge rate slowed considerably, partly because of small, episodic recharges generated by effective rainfall and partly because of a drop in abstraction demand.

Rainfall in late August and September 2025 led to the first recharge episodes in reactive and inertial aquifers in the south-western Paris Basin and the Rhône corridor. September 2025 marked the transition from discharging to recharging.

Low-water period (end of discharge period)

The 2025 lowest-water levels were recorded slightly earlier, between the end of August and September 2025, in many reactive aquifers in the southern two-thirds and north-east of the country. The first recharge events were observed towards the end of August 2025 with late summer storms. Then the accumulated rainfall at the end of August and September 2025 was sufficient to infiltrate deep down and reverse the trends in aquifers. In addition, the drop in temperatures reduced the amount of water needed by vegetation, meaning more rainfall was able to reach the aquifers. Discharge continued at the end of September 2025 for the reactive aquifers of the Armorican Massif, despite small recharge episodes, and for some aquifers in the centre and west of the Aquitaine Basin, in a context of a lack of effective local rainfall.

In September 2025, a few rising levels were recorded locally in the inertial aquifers of the south-western Paris Basin and the region east of Lyon, as a result of high rainfall accumulation and less abstraction. However, most of the inertial aquifers had not begun to recharge by the end of September, and their levels continued to fall. This scenario is quite normal in September, since it can take several weeks for rainfall to seep deep into the ground.

Aquifer situation at the end of the discharge period

The situation during the low-water period in 2025 depended on the high-water situation in 2025, the duration and intensity of the discharge in 2025, the abstraction demands placed on the aquifers and their cyclicity.

Reactive aquifers, which have annual cycles, are sensitive to drought conditions and their levels were supported by occasional recharges caused by rainfall in spring and, to a lesser extent, summer.

The early start of the 2025 discharge, in February or March, led to a deterioration in the situation of the aquifers in the northern and central half of the country (Boulonnais, Grand-Est, Jura, northern and central Massif Central, northern Armorican Massif). The stormy spells that occurred during the summer of 2025, particularly in the north-east, helped to support water levels and slowed the deterioration in the state of the aquifers. The Massif Central basement aquifers suffered particularly badly from the lack of rainfall over the summer. Fortunately, the 2025 low-water level was reached early, at the end of August, which halted the deterioration so that recorded low-water levels ranged from close to normal to moderately low. There were a few low to very low water levels in the Limousin basement aquifers.

In the southern half of the country (south of the Armorican Massif, the Aquitaine Basin, along the Mediterranean coastline and in Corsica) the discharge period was short and less intensive. Rainfall in the spring and summer of 2025 provided occasional support for water levels. Favourable 2025 low-water levels were recorded, usually as being normal to high. Surplus levels, from moderately high to high, were recorded for aquifers that received support from rainfall in July and August 2025, just before the low-water period (upstream Garonne, western Languedoc, Provence and Côte d'Azur). The situation remained very fragile throughout the 2025 discharge period, resulting in moderately low to low levels during the low-water period in 2025 in the aquifers of the Roussillon plain, the Corbières massif and the Aude valley.

Inertial aquifers, whose cycles cover several years, are not particularly sensitive to the weather conditions that occur during the discharge period: they are highly resistant to drought and rarely react to summer rainfall. The 2025 discharge period was characterised by a gradual deterioration in aquifer states, reaching levels that were generally satisfactory during the 2025 low-water period, ranging from close to normal to high levels. In the Artois and Paris Basin, the 2025 discharge period was long, but levels generally remained moderately high to high. The low-water situations in 2025 were worse for the less inertial marl chalk aquifers on the Artois and Champagne coasts, which were more sensitive to the rainfall deficits that occurred from February 2025 onwards. On the other hand, the situation was particularly satisfactory, with a surplus, in the highly inertial Beauce aquifer. The 2025 discharge of the Sundgau (southern Alsace) and the Rhône-Saône corridor aquifers was not very intense, and their respective situations changed little during the spring and summer. Levels during the low-water period in 2025 were generally comparable to normal to high levels.