  The balancing provided by hydropower reservoirs is essential in the transition towards a decarbonised European energy system, but the resource might be impacted by future climate change. In this work, we first analyse the hydropower operation needed to balance a wind and solar dominated European energy system, to signify whether and to what extent hydropower is required to operate differently due to the decarbonisation of the energy system. Second, we apply runoff data achieved with 10 dynamically downscaled climate models with 0.11 x 0.11 deg horizontal and daily resolution to project the future reservoir inflow at three CO2 emissions scenarios: low (RCP2.6), mid (RCP4.5), and high emissions (RCP8.5). We show that the decarbonised energy system increases the ramp rates and seasonality of the hydropower operation. Despite large interannual and intermodel variability, we found a significant change in annual inflow due to climate change in 20 out of 22 European countries at the mid and high emissions scenarios. The seasonal profile, as well as the frequency and duration of droughts and floods, is also projected to be impacted. 
Future operation of hydropower in Europe under high renewable   penetration and climate change