Tobias Wechsler , Florian Lustenberger, Andreas Inderwildi, Jacob Hirschberg, Bettina Schaefli, Massimiliano Zappa

Alpine regions are particularly sensitive to climate change due to the pronounced effect on snow and glacial melt. In this context, large perialpine lakes play a crucial role in modulating climate change impacts on water resources, which brings together diverse interests. However, climate change studies on river systems rarely include lakes or lake level management. An open question is how to incorporate lake level management effects into hydrologic simulations to project climate change impacts. This study focuses on four perialpine lakes in Switzerland, with different levels of lake level management. We combine the hydrologic model PREVAH with the hydrodynamic model MIKE11 to simulate lake level and outflow scenarios from 1981 to 2099, using the Swiss climate change scenarios CH2018. The hydrological projections at the end of the century show pronounced seasonal changes in lake levels, characterised by an increase in winter and a decrease in summer when water demand is highest. Without climate mitigation measures, this summer decrease ranges from -0.04 m for a regulated lake to -0.4 m for an unregulated lake. In addition, the simulations indicate more frequent drought events. The projected changes intensify with time and missing climate mitigation measures. Future work could focus on interannual variability to explore regulatory strategies under changing conditions.