Groundwater sustains human well-being and the functioning of ecosystems. Many regions in Europe have experienced declining groundwater levels caused by decreasing groundwater recharge (GWR) or increasing groundwater abstractions (GWAs). These changes can lead to groundwater-related stress, threatening both ecosystems and water supplies. Existing groundwater stress indicators estimate stress during a given period but do not address how stress changes or show the uncertainty of future stress. We propose a novel indicator of future groundwater stress (GWSI) due to changes in GWR and GWA and, thus, the alteration of long-term mean annual groundwater discharge (GWD). Groundwater stress is defined as any alteration in GWD since ecosystems are adapted to an equilibrium state. Focusing on decreasing GWD, which is generally more harmful than increasing GWD, we quantified the future GWSI in Europe by integrating scenarios of GWR and GWA in 2070-2099. GWR was evaluated using an ISIMIP2b multi-model ensemble of eight global hydrological models driven by the output of four global climate models under two greenhouse gas emission scenarios. GWA scenarios for irrigation, domestic and manufacturing sectors were combined with the GWR projections to generate an ensemble of GWSIs, simplified into three groundwater stress scenarios (high, intermediate, low). Projected GWSIs vary significantly among the scenarios. For the high-stress scenario, 58 % of Europe's land area is projected to experience a GWD decrease of at least 25 % under RCP8.5 compared to 38 % under RCP2.6, while the respective values are 26 % and 1 % for the intermediate-stress scenario. Groundwater demand management alone cannot prevent GWD declines under the high-stress and intermediate scenarios, in particular under RCP8.5. Therefore, climate change mitigation is imperative for reducing the decline of GWD, especially in Eastern and Southeastern Europe, where changes in GWR are the primary cause of declining GWD (in the high abstraction scenario under RCP8.5). Under RCP2.6, reductions in GWAs by 25-75 % would balance a GWD decline in parts of Spain and Italy where GWAs are high, even in the high-stress scenario. In line with the precautionary principle, we recommend adapting to the high-stress scenario to minimize harm to the beneficiaries of groundwater.

The dataset includes R scripts for processing, analyzing, and visualizing groundwater recharge (GWR), groundwater abstraction (GWA), groundwater discharge (GWD) and groundwater stress (GWS) data for Europe as presented in the paper "Groundwater Stress in Europe – Assessing Uncertainties in Future Groundwater Discharge Alterations due to Water Abstractions and Climate Change", submitted to Frontiers in Water. The filenames of the scripts are numbered in chronological order to reproduce the steps described in the paper. All necessary packages are listed within the scripts. Links to publicly available data used in the scripts are also provided. For any data that is not publicly available, a note is included in the respective code line, indicating that the data can be requested from the author.