Assessment of Climate Change Impacts on Water Resources in the Somme River Basin (France)

Modelling the impacts of climate change on water resources in the Somme watershed in northern France is investigated with a multimodel ensemble to probe the sensitivity of hydrologic response to uncertainties in climate projections provided by general circulation models. At the Somme watershed scale, the average decrease in predicted recharge from seven climate models is -18.7%. However, significant disparities appear between simulation results for different climate models. These variations are bounded between -30.4% for the most pessimistic model and-5.6% for the most optimistic model. Moreover, seasonal gaps are markedly important. For all climate models, the impacts on groundwater levels would be greater on plateaus than in humid valleys. The water level changes would be on the order of -10m on the plateaus for five climate models and between 0.2m and 0.5m in humid valleys. The impacts of two other climate models on water levels are rather low. In addition, the monthly average discharge of the Somme River and its tributaries is predicted to decrease by 2065. The seven-model average shows that the low outlet flow rate to the Somme basin would be reduced by 23% but with disparities between models. The decrease would be more severe in the Avre basin, with the minimal discharge reduced by 32%. This study is a first step towards addressing uncertainties in climate models such that an adaptive watershed management strategy could be devised for water resource managers.