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

The society is adapted to the current seasonality and variations in water balance and water availability. In Norway more than 90% of the electricity production is based on hydropower, and to meet the energy demand, reservoirs are used to store water across seasons as runoff is generally lowest in winter when the energy demand is the highest. The aim for electricity production and operation of hydropower reservoirs is to maximize income for hydropower companies. The day-to-day decision of power production is based on energy demand, electricity prices and water availability. The main constraints for reservoir operations are minimum and maximum water levels as well as minimum flow requirements downstream. To make the best possible decisions for the future, hydrological models are used to provide expected runoff that is used by an energy marked model to suggest reservoir operations. A changing climate might result in changes in both annual runoff and seasonality of runoff, that might lead to changes in energy production and reservoir management.

Here, as part of the HorizonEurope project STARS4Water, we aim to assess how climate changes might impact reservoir operations and water stress in the Drammen River basin. This will be achieved by using two gridded hydrologic models (HBV and LISFLOOD) to simulate runoff for a reference period and a future period under downscaled climate scenarios. . Thereafter the energy marked model EOPS will be used to simulate reservoir operations for the two climate periods assuming that the electricity prices are unchanged. EOPS is used for sub-areas or river basins, has a detailed representation of the hydropower system, and requires reservoir inflows and energy prices as inputs. When prioritizing between the different constraints, the strongest ones are the minimum and maximum water levels in the reservoirs. During droughts, EOPS might deliver less water than required for environmental flows to avoid violating other requirements or limitations.

To assess climate change impacts, the changes in reservoir inflow, water levels and periods with water stress (i.e. the minimum flow requirements are not met) and full reservoirs that might increase flood risk, will be compared.