Map of aquifer levels in mainland France on 15 September 2026. Map drawn up by BRGM on 17 September 2026, based on data acquired up to 15 September 2026.
© BRGM
Trends observed on piezometers on 15 September 2026.
© BRGM
Groundwater trends
At 15 September, groundwater levels continued to decrease at 81% of observation points.
The vast majority of aquifers were concerned by this decrease, which is to be expected at the end of summer, even though we should now be coming to the end of the low-water period. The soil remained dry and the isolated showers that occurred in August were above all beneficial for the vegetation but produced little effective rainfall. Moreover, much of the rain in August fell during storm episodes, which tend to generate more surface run-off and therefore less infiltration. Equally, the high temperatures resulted in increased abstractions, which exacerbated the natural decrease in groundwater levels, which is typical at this time of year.
Aquifers with slow response times
Regarding aquifers with slow response times, only those in the limestone formations of Sundgau remained stable. Levels dropped in the chalk aquifers of Artois and Normandy and in the formations of the Paris Basin, as well as in the Vosgian sandstone formations and the Triassic limestone aquifers of Lorraine. The same was true for the aquifers in the Rhône-Saône corridor and in the fluvio-glacial formations to the east of Lyon as well as for the aquifers in the Savoie foothills and in the tawny sand formations of the Armagnac region.
Aquifers with rapid response times
Concerning responsive aquifers, the prevailing trend was downwards. However, levels stabilised in the basement aquifers of the Cévennes, Margeride, Ségala and the Montagne Noire, and in the karst aquifers of the Causses (Quercy and Grands Causses), as well as in the Cretaceous and Tertiary limestone aquifers of Sologne and the Sancerre region. Stable levels were also recorded in several alluvial aquifers and certain related Tertiary basins (the southern plain of Alsace, the lower Rhône and its main tributaries, Limagne, the Corsican coast and the Côte d’Azur, as well as the Hérault, Orb, Aude, Adour and Gaves river basins).
Situation observed on piezometers on 15 September 2026.
© BRGM
Overall groundwater situation
Aquifers with slow response times
The situation in less-responsive aquifers has not changed since 1 September:
- Groundwater levels in the Beauce and Armagnac limestone aquifers remained moderately high.
- The levels in the Pliocene aquifers of the Sundgau and Roussillon regions and in the fluvio-glacial formations of eastern Lyon were around average for this time of year.
- Levels were moderately low in the chalk aquifers of the Artois and Normandy regions, in the formations of the Paris Basin and the Rhône-Saône corridor as well as in the fluvio-glacial deposits of the Bas-Dauphiné and Savoie foothills.
- Finally, the levels observed in the aquifers in the Vosgian sandstone formations and in the Triassic limestone of Lorraine remained low.
Aquifers with rapid response times
As regards responsive aquifers, the situation generally remained stable in August, with some local variations, since the month was generally less dry than previous months.
The situation deteriorated in five areas:
- Water levels in the alluvial aquifers of the Hérault and Orb rivers fell from moderately high to around average.
- Levels decreased from around average to moderately low in the alluvial and Tertiary aquifers in the Lower Rhône and Durance basins, as well as in the basement formations of the Cévennes, Margeride, Ségala and Montagne Noire.
- Groundwater levels in the fluvial and fluvio-glacial alluvial formations of the Upper Rhône and its tributaries fell from moderately low to low.
- Finally, the groundwater levels in the basement formations of Morvan, Livradois, Forez and Vivarais went from low to very low.
On the other hand, the situation improved in five other areas:
- Groundwater levels in the northern Alsace plain went from very low to low.
- The levels in the aquifers in the Plioquaternary formations of the Aquitaine Basin and in the Lower Cretaceous sand formations on the eastern edge of the Paris Basin improved from low to moderately low.
- The level of the alluvial aquifer in the Aude basin rose from moderately low to around average.
- Finally, the level in the Astian sand aquifer in the Valras-Agde area went from high to very high.
In addition to the aquifers in the Morvan, Livradois, Forez and Vivarais regions, the aquifers located in the neighbouring Limousin and Chataigneraie plateau and in the karst limestone formations of Jura continued to show very low levels.
At the other end of the spectrum, in addition to the very high levels observed in the Astian sand aquifer of the Valras-Agde region, high levels were also recorded in the neighbouring Vistrenque aquifer, while moderately high levels were observed in the alluvial aquifers along the coastal area of the Roussillon plain, as well as in those of the lower Rhône basin and its main tributaries.
Forecasts
A predominantly downward trend is expected over the coming weeks, with Météo-France forecasting a high-pressure system over France and generally dry weather in the short term. However, the lower temperatures will reduce abstractions for the supply of drinking water and for irrigation and should ease the pressure on groundwater resources.
Aquifers with slow response times
The forecast for less-responsive aquifers remains uncertain. If too little rain falls, it will only be enough to meet the needs of vegetation, leaving no water to recharge the aquifers. Groundwater levels are expected to reach normal or moderately low levels in these aquifers in the coming weeks. The aquifers in the Vosgian sandstone formations and in the Triassic limestone aquifers of Lorraine will need to be closely monitored, since their levels are already low.
Aquifers with rapid response times
Regarding responsive aquifers whose levels are currently above average, the forecast for the next few weeks is quite positive. For the others, the long-term forecast is much less certain, and whether levels remain satisfactory will depend on rainfall in the coming weeks. Considering the needs of vegetation and abstraction levels that remain relatively high, if there is little rain in the coming weeks, the situation in responsive aquifers whose levels are already very low – such as certain basement aquifers in the Massif Central (Limousin and Chataigneraie plateau, Morvan, Livradois, Forez and Vivarais) and the karst limestone aquifers in the Jura – could deteriorate further.
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). These global indicators reflect general situations and trends and do not take into account possible local disparities.
The "Aquifer levels" indicator (colours) 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-shaded areas are areas where there are no extensive unconfined aquifers and/or no monitoring points. 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).
Data source: ADES (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).