What is impacting transboundary aquifers? Climate or global changes?

In Eastern Belgium, one of the main groundwater reservoirs is located in Cretaceous chalk geological formations. The recharge zone of this aquifer corresponds to the Hesbaye chalk aquifer of the Geer basin, in the Walloon region of Belgium (Groundwater body BERWM040). In Flanders, the chalk layer deepens to the North-West where it becomes confined under Tertiary sediments (Groundwater body BLKS_1100_GWL_1M).

Groundwater from this chalk aquifer has been exploited for decades by different water companies, through pumping wells and galleries. These last decades, groundwater level time series have started to exhibit decreases, particularly in the recharge zone, when comparing the 1960-1990 and 1990-2020 periods. These decreases have been mostly attributed to first signals of climate change, with observed temperature increase and precipitation decrease, inducing a decrease of recharge. However, hydrogeological budgets calculated over different time periods for the Walloon part of the catchment have indicated increased water losses, attributed to a probable increase of groundwater abstraction in the Flemish part of the aquifer.

All these results are reanalysed here in terms of water budget, evolution of groundwater levels and changes in indicators reflecting the pressure of groundwater abstraction on the evolution of groundwater reserves. Conclusions show that climate change is indeed a driver but increased anthropogenic pressure is also likely to be a key controlling factor. Based on this analysis, conclusions are drawn in terms of the need for efficient integrated transboundary management of such very important groundwater resources in a context of global change.