Groundwater storage in alpine catchments and response to climate change: the importance of geology and snow cover

Alpine areas play a major role in the water supply of downstream valleys by releasing water, and especially during dry periods. The response of catchment discharge to climate change can be significantly influenced by groundwater processes. However, these processes are still poorly understood in Alpine areas. In this study, we use isotopic monitoring of a small alpine catchment to investigate the evolution of snowpack isotopic composition and its implications for groundwater recharge assessment. The results highlight the dominant contribution of snowmelt to recharge processes in the studied alpine catchment located in the Swiss Alps. This finding is critical for improving the evaluation of alpine hydrological responses under future climate change.Then, we apply an integrated surface–subsurface hydrological model to assess the role of groundwater in buffering future summer low flows and to provide new insights into the influence of geological controls on discharge dynamics. The spatially explicit modelling framework enables the quantification of groundwater storage and its variability across different geological units within an alpine catchment under both present and future climate conditions. In parallel, conceptual hydrological models are used to assess future changes in spring discharge in different alpine settings, these resources being particularly relevant for drinking water supplies. The used climate scenarios were CH2018 RCP 8.5 and 4.5.The results suggest that under future extreme climate change conditions: the average groundwater storage in quaternary deposits at the catchment scale increases in winter and decreases in summer as well as spring and catchment discharges. Annual groundwater storage for the entire catchment decreases due to a reduction in mean annual groundwater recharge, and total catchment discharge also decreases. In relative terms, the modelled decrease in groundwater storage was less severe than the simulated decrease in discharge in the analysed climate change scenarios. This study demonstrates that both quaternary deposits (especially moraine and talus units) and bedrock play an important role in sustaining discharge during low-flow periods.