Groundwater tables on 1 September 2022

The groundwater recharging period during the winter of 2021-2022 was short and well below average across the country. Groundwater tables began to empty between January and March, two to three months early, with levels remaining on a downward trend overall throughout the spring and summer. During the spring, discharge was faster than usual, owing to a deficit in rainfall combined with strong demand for water.

In August, levels were low for almost all groundwater tables. Aquifers drain naturally into rivers, thereby maintaining low-water levels, while abstractions continue. The intensity of the depletion process slowed down in many aquifers across France, in July and August. This can be explained by the limits placed on abstraction and by occasional recharging periods following effective local rainfall.

However, the storms in August had little impact on the groundwater tables. The quantity of rainfall infiltrating at depth remains low or non-existent, owing to the very dry soils and the consumption of this water by vegetation. Locally, rainfall led to slight, occasional recharging. As a result, trends are stable on the unconfined karstic limestone aquifers located in the region of Les Causses. In the south-east, rainfall was insufficient to recharge the groundwater tables, even though slight temporary rises were observed.

The 2021-2022 recharging period was short with little rain, leaving the groundwater tables in an unsatisfactory state at the end of winter. The situation deteriorated rapidly during the spring, owing to high demand for groundwater, and more gradually over the summer.

Since July, the state of the groundwater tables has remained virtually unchanged, owing to low local effective rainfall and, more probably, to a decrease in the demand for water. Introducing restrictions on the use of water made it possible to limit abstraction and thus to reduce the pressure on groundwater tables. In August, however, levels remained unsatisfactory, ranging from around the monthly average to very low.

The inertia of the groundwater tables in the north of France and the Rhône-Saône corridor indicates strong resistance to summer droughts. As a result, the situation of these aquifers has remained virtually unchanged since June. Levels are low to around average for aquifers in the Paris Basin. However, the situation often varies considerably at local level, particularly in sectors with heavy demand for abstractions. The levels are more worrying in the Rhône-Saône corridor, ranging from moderately low to low.

Reactive groundwater tables are sensitive to a lack of effective rainfall, with the situation gradually deteriorating between July and August. Levels are currently ranging from moderately low to well below monthly averages in much of the country, which is a cause for concern. They remain satisfactory and close to normal in the south-west.

The situation was relatively positive for several aquifers, where levels in August were close to normal, compared to previous years:

• Since June 2022, levels have remained close to normal for the Tertiary groundwater tables between the Brie and the Tardenois, which are inertial and resistant to drought;
• The alluvial aquifers of the Adour and Gave de Pau rivers and their main tributaries were recharged several times during the spring, so levels remain close to monthly norms;
• The ground water levels of the Roussillon plain are comparable overall to normal levels, but with significant variations, from moderately low on the Quaternary surface groundwater table to high on the deep Pliocene groundwater table.

Many aquifers are in an unfavourable condition, with levels that are low or extremely low, compared to the situation observed in August in previous years:

• In the north-east, the situation is continuing to deteriorate. Levels are low in the Champagne chalk aquifers, the Jurassic limestone aquifers from Lorraine to the Côte-des-Bar, and the alluvial aquifers of the Alsace plain;
• In the centre-west region, the levels of the basement aquifers of the Armorican Massif, the Jurassic limestone aquifers of Bessin, Poitou and Brenne, the Maine sand aquifer and the Touraine chalk aquifer are low, or even very low in some places, as a result of the deficit in rainfall during the winter and spring;
• In the centre-east, the levels of the inertial plio-quaternary gravel aquifers of Burgundy-Franche-Comté, the alluvial aquifers and the river-glacier corridors of the middle Rhône and the Miocene molasse of the Bas-Dauphiné are low to very low, following several successive insufficient recharges and a gradual deterioration since the beginning of the year;
• In the south-east, the levels of the alluvial aquifers and the complex formations of Provence and the Côte d'Azur are continuing to cause concern. Levels remain low to very low, owing to insufficient recharging in both 2020-2021 and 2021-2022. Note that the karstic limestone resources of the Vaucluse and central Var are drying up, heralding a severe low-water period.

According to the seasonal forecasts of Météo-France conditions are expected to remain "hotter than normal" for the next quarter. No clear scenario has emerged for rainfall. However, significant accumulated rainfall, such as intense Mediterranean episodes, could occur locally.

In September, rainfall events are not expected to recharge groundwater tables to any significant extent. The current situation of extremely dry soil and heavy rainfall is more likely to lead to runoff. Further, any rainfall infiltrating the soil will initially moisten the ground and benefit the vegetation. Effective rainfall is not therefore expected to infiltrate deeply into the groundwater table.

This situation is expected to continue during September, or to deteriorate more or less rapidly depending on the demand for water and the sensitivity of the aquifers to drought. In the event of significant local rainfall, the situation could, however, improve temporarily for the most reactive aquifers. However, levels are not expected to rise above September norms in the case of aquifers where levels are currently low to very low.

In the medium term, the process of drainage is expected to continue until the vegetation becomes dormant and significant rainfall occurs. Trends and changes in the situation will mainly depend on effective local rainfall, the demand for water and the inertia/reactivity of the groundwater table.

In the case of inertial aquifers, levels are unlikely to rise before mid-October-November and no improvement is expected before mid-autumn. The situation could become worrying, with severe low-water levels for the inertial aquifers of the Rhône-Saône corridor, as well as for aquifers in the south (Touraine and southern Beauce) and in the north-east (Champagne) of the Paris Basin.

Concerning reactive aquifers, a particularly severe low-water level is expected in many areas, with the exception of those in the south-west. In the event of insufficient rainfall, many reactive water tables could fall to low or very low levels by September-October.

Over the coming weeks, in the absence of sufficient effective rainfall, the only solution for protecting the aquifers and maintaining continuity between groundwater and surface water will be to limit water abstraction. Restrictions on the use of water help to relieve the pressure on water resources. Slowing down the process of discharge avoids rapid deterioration of the aquifers and postpones the occurrence of severe low water in rivers pending the arrival of effective rainfall. However, given the current situation, groundwater levels at the start of the 2022-2023 winter period will be significantly lower than last year, with the majority varying between low and very low.

During the autumn, winter and early spring, it will be necessary to monitor the situation for all groundwater tables across the country, particularly those with severe low-water levels. The replenishment of groundwater reserves and the return to normal levels at the end of winter 2023 will only be possible if resources are abundantly recharged over the autumn and winter. Note that spring rain will also push back the start of the drainage period for the most reactive water tables.