Simulating climate change impacts on the thermal structure of lakes at a wide range of altitudes

Climate change is expected to modify the thermal structure and the mixing regimes of lakes, with important consequences for the nutrient and oxygen dynamics as well as lake ecology. Here, we simulated the impact of projected climate change on the thermal structure and the ice cover of 29 Swiss lakes using the one-dimensional, vertically resolved, hydrodynamic model Simstrat. The selected lakes cover a wide range of depths, sizes and water quality and an altitude range from 200 to 1800 m a.s.l. For 27 of the 29 lakes, the model was calibrated with observed temperature profiles. Simulations were performed for the IPCC RCP8.5, RCP4.5 and RCP2.6 greenhouse gas emission scenarios and were forced with a total of 31 GCM-RCM model chains selected from the ensemble of the CH2018 climate scenarios and downscaled to the individual lake locations. The results show a clear altitude- and size-dependence of the sensitivity of different lake thermal characteristics to projected climate change. For example, a larger prolongation of summer stratification is projected for small and high altitude lakes. Conversely, larger and lower-altitude lakes are projected to experience a stronger increase in deepwater temperatures. This variable climate sensitivity needs to be considered when assessing potential climate impacts on physical, chemical and ecological processes in lakes.