The future of Swiss run-of-river hydropower production: climate change, environmental flow requirements and technical production potential

Run-of-river (RoR) hydropower is essential in Alpine energy production and highly sensitive to climate change, due to no or limited water storage capacity. Here, we estimate climate change impact on 21 RoR plants in Switzerland, where 60% of the annual electricity is produced by hydropower (30% by RoR). This is one of the first comprehensive, simulation-based studies on climate change impacts on Alpine RoR production, including effects of environmental flow requirements and technical production potential. We simulate three future periods under three emission scenarios (RCP2.6, RCP4.5, RCP8.5). The results show an increase of winter and a decrease of summer production, which in conjunction leads to an annual decrease. The simulated impacts strongly depend on the elevation and the plant-specific characteristics. A key result is that the climate induced reduction is not linearly related to the underlying streamflow reduction, but is modulated by environmental flow requirements, the design discharge and streamflow projections. Stronger impacts are expected if climate change affects streamflow in the range that is usable for production. This result is transferable to RoR production in similar settings and should be considered in future assessments. Future work could in particular focus on further technical optimisation potential, considering detailed operational data.