Climate change impacts on water availability and hydropower production – a case study from Drammen river basin in Norway 

Close to 90% of the electricity production in Norway originate from hydropower. To match the energy supply with the demand water is stored in reservoirs in summer when reservoir inflow is high and production is high, and released in winter when the demand is the highest and inflow is small. As the management of hydropower reservoirs aims to maximize income, the day-to-day decision of power production, and reservoir release, is based on electricity prices and constrained by minimum and maximum reservoir water levels as well as minimum flow requirements downstream.As a part of the HorizonEurope project STARS4Water, we aim to assess how climate changes might impact reservoir inflows, hydropower production, reservoir operations in the Drammen River basin in southern Norway. In particular we have analyzed the climate change impacts on the seasonality and year-to-year variability of energy inflow to the reservoirs, reservoirs water levels and how much of changes in energy inflow impacts the power production. To assess climate change impacts, downscaled scenarios from several combinations of GCMs, RCMs, and bias correction algorithms from both Coupled Model Intercomparison Project Phase 5 (CMIP5) and CMIP6 are used. We have used two gridded hydrologic models (HBV and LISFLOOD) to simulate runoff for a reference period and two future periods driven by the downscaled climate projections. Thereafter, the energy marked model EOPS (One-area Power-market Simulator) has been used to simulate reservoir operations. EOPS is used for sub-areas or river basins, has a detailed representation of the hydropower system, including environmental restrictions, and requires inflows and energy prices as inputs. Based on the outputs from the hydrological models and EOPS, the changes in water balance, reservoir inflow, water levels, and – outflows, and energy production are analysed and compared.