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Box 3-2 Climate change will lower groundwater levels in the Loire and southwestern France

Sources: (Maréchal and Rouillard, 2020; Delgoulet, 2015)

The Explore 2070 project has developed and assessed strategies to adapt to climate change impacts on hydrological systems and coastal environments in mainland and overseas France up to 2070, based on different climatic, demographic and socio-economic scenarios. Rises in temperature (and consequently evapotranspiration) combined with decreasing rainfall, will lead to a decrease of effective precipitation in the future. The application of seven climate models using the median Green House Gas (GHG) emission scenario (A1B, fourth GIEC report) enabled an estimate of the change in natural recharge rates. With predicted recharge variations of +10 to −30% in the optimistic scenarios, and −20 to −55% in the pessimistic scenarios, a decline of similar proportions in groundwater levels would be expected, and therefore groundwater resources are likely to decline significantly overall by 2070. Two areas which are likely to be more severely affected are the Loire basin with a 25–30% recharge decline across half of the basin area, and the south-west of France with a 30–50% decline in recharge. All of the scenarios also show a decline in average river flow by 2065, which varies from a 10 to 40% reduction in the northern half of the country, and a 30–50% reduction in the southern half, with local extremes of up to 70%. Despite this relative decline in river flow, some models show that very high surface water levels are nevertheless possible during the winter in some catchments (e.g. the Somme and Rhine Rivers), confirming the likelihood of lengthy periods of flooding.

Furthermore, water balance studies have shown that many catchments and aquifers present high structural water deficits, impacting environmental flows, leading to the imposition of abstraction caps on water users, in particular agricultural irrigation. In addition, over the last twelve years, more than 50% of the French departments concerned by restriction orders of use - watering, filling swimming pools, cleaning vehicles, etc. - in 2003, 2005, 2006 and 2011. The recurrence of these episodes of water stress has made it necessary to reinforce the security of the supply of drinking water services.