Climate change impacts on future snow, ice and rain runoff in a Swiss mountain catchment using multi-dataset calibration

•The hydrological model was calibrated to discharge, snow cover and glacier mass balances.•Multi-dataset calibration yields more realistic simulations, than calibration to discharge only.•Multi-dataset calibration reduces the uncertainty in glacial melt runoff scenarios.•Glaciers in the Gigerwald catchment are projected to disappear as a consequence of climate change.•Discharge will increase during winter and early spring and decrease in summer and early fall.

Study regionThe hydropower reservoir of Gigerwald is located in the alpine valley Calfeisental in eastern Switzerland. The lake is fed by runoff from rain, snow melt and ice melt from a few small glaciers, as well as by water collected in a neighbouring valley.Study focusWater resources in the Alps are projected to undergo substantial changes in the coming decades. It is therefore essential to explore climate change impacts in catchments with hydropower facilities. We present a multi-dataset calibration (MDC) using discharge, snowcover data and glacier mass balances for an ensemble of hydrological simulations performed using the Hydrologiska Byråns Vattenbalansavdelning (HBV)-light model. The objective is to predict the future changes in hydrological processes in the catchment and to assess the benefits of a MDC compared to a traditional calibration to discharge only.New hydrological insights for the regionWe found that the annual runoff dynamics will undergo significant changes with more runoff in winter and less in summer by shifting parts of the summer melt runoff to an earlier peak in spring. We furthermore found that the MDC reduces the uncertainty in the projections of glacial runoff and leads to a different distribution of runoff throughout the year than if calibrated to discharge only. We therefore argue that MDC leads to more consistent model results by representing the runoff generation processes more realistically.