Ensemble modelling of ice cover for a reservoir affected by pumped-storage operation and climate change

Ensemble modelling was used to assess the robustness of projected impacts of pumped-storage (PS) operation and climate change on reservoir ice cover. To this end, three one-dimensional and a two-dimensional laterally averaged hydrodynamic model were set up. For the latter, the strength of the impacts with increasing distance from the dam was also investigated. Climate change effects were simulated by forcing the models with 150 years of synthetic meteorological time series created with a weather generator based on available air temperature scenarios for Switzerland. Future climate by the end of the 21(st) century was projected to shorten the ice-covered period by similar to 2 months and decrease ice thicknesses by similar to 13 cm. Under current climate conditions, the ice cover would already be affected by extended PS operation. For example, the average probability of ice coverage on a specific day was projected to decrease by similar to 13% for current climate and could further be reduced from similar to 45% to similar to 10% for future climate. Overall, the results of all models were consistent. Although the number of winters without ice cover was projected to increase for all one-dimensional models, studying individual segments of the two-dimensional model showed that the impact was pronounced for segments close to the PS intake/outlet. In summary, the reservoir's ice cover is expected to partially vanish with higher probability of open water conditions closer to the PS intake/outlet.