Groundwater storage in Quaternary deposits and bedrock buffers the discharge response of a small alpine catchment to climate change

Abstract Alpine areas play a major role in the water supply of downstream valleys by releasing water during dry periods. Groundwater storage could significantly influence how changing climatic conditions affect the discharge regime. However, these processes are still not well understood in alpine areas. Studies on how climate change impacts water resources in alpine areas rarely consider the influence of geology explicitly. An integrated surface–subsurface hydrologic model (HydroGeoSphere) was used to highlight the effect of groundwater in buffering future summer low flows and to give new insights into the role of geology in controlling discharge. The spatially explicit model allows the quantification of groundwater storage and its variation in different geological formations of an alpine catchment, under current and future conditions. The results suggest that, under future extreme climate change conditions, the average catchment groundwater storage in Quaternary deposits increases in winter and decreases in summer; the annual mean groundwater storage for the entire catchment decreases due to the decrease in mean annual groundwater recharge; and the total catchment discharge decreases and low-flow period shifts from winter to late summer by the end of this century. Future summer low flows will remain higher than the current winter low flows but will approach them closely after very dry summers. Proportionally, the decrease in groundwater storage will be less severe than the decrease in discharge. Finally, a sensitivity analysis illustrates that both Quaternary deposits (especially moraine and talus units) and bedrock play an important role in supporting discharge during low-flow periods.