Study of the impact of climate change on the availability of water resources in the Somme catchment area

The need

Climate change has an impact on the water cycle and water reserves. Due to the pressures exerted and the hydrogeological context, the surface water and groundwater resources of the Somme catchment area appear to be particularly vulnerable to climate change, the quantitative impacts of which are estimated using the hydrogeological model of the Somme developed by BRGM since 2000.

The results

The climate forcing factors were selected from the DRIAS portal, which provides climate projections by region in various graphical or numerical forms, produced by French climate modelling laboratories (IPSL, CERFACS, CNRM). Given the uncertainties of the climate models with regard to rainfall, a narrative approach has been adopted that considers two contrasting projections (a hot, dry climate and a median climate with limited changes).

The general trend in mean piezometric anomalies and mean flows suggests that in the short term (up to 2040) it will be slightly wetter, while the medium term (2041-2070) shows dry anomalies that become more pronounced or, on the contrary, invert in the long term (2071-2100) depending on the projection: the contrasted projection shows marked dry anomalies over the whole catchment area, while the median projection shows wet anomalies.

Projecting current abstraction rates into future scenarios shows that they exacerbate low water levels and droughts. The resource is highly stressed in some of the management units of the catchment area, intensifying conflicts between different uses (irrigation, drinking water supply and industry) in the context of climate change.

With regard to extreme events (hydrogeological low and high water), low/high water and low/maximum flow episodes become more frequent, longer and more intense from the medium term onwards than over the current period. In other words, current extremes will be normal in the future.

Finally, the implementation of abstraction reduction scenarios (National Water Plan) has shown that it is possible to maintain water resources in their current state in the near future. However, further reductions will be necessary from 2040 and beyond to conserve the water system.