Adapting Hydropower Operations to Support Renewable Energy Transitions and Freshwater Sustainability in the Columbia River Basin

There is unequivocal evidence that the Earth is warming at an unprecedented rate, and that the burning of fossil fuels is the principal cause. This situation is fostering a growing interest in shifting global energy production toward renewable energy sources such as solar, wind, and hydropower. Hydropower plays an important role in meeting global carbon mitigation targets and eventually achieving net-zero carbon emissions, especially within the Mid-Columbia (Mid-C) energy market in the Pacific Northwest (PNW), where hydropower currently comprises 50-65% of its generation. However, other renewable energy sources in the Mid-C market and connected California Independent System Operator (CAISO) power grid are expanding significantly, particularly solar power in California (CA). Thus, hydropower operations at plants within the connected Mid-C market may need to be re-operated to balance the more intermittent supply from renewables in CA so that energy supplies are in phase with demands. In this study, our goal is to re-design hydropower operations in the Columbia River Basin (CRB) of the PNW to achieve a 95% renewable energy power grid in CA and the PNW by the year 2035. This will require not only filling supply gaps from other renewable energy sources, but also balancing other conflicting objectives to be fulfilled by the dam operations, such as minimizing environmental spill violations, maximizing hydropower production, maximizing flood protection, and maximizing economic benefits. We use multi-objective optimization to design alternative operations at four CRB dams to balance these objectives over the historical record. We then simulate their operations over alternative possible future climate change and energy development scenarios to find a recommended set of operations that are robust to these uncertainties. The energy scenarios include the National Renewable Energy Lab’s (NREL) Mid-Case Energy Scenario for the years 2025, 2030 and 2035, which achieve 95% Renewables by 2035, as well as a business as usual (BAU), or base case, scenario represented by the historical energy mix. The four climate scenarios are made from combinations of low or high warming and low or high streamflow for three overlapping time steps: 2020-2029, 2025-2034, and 2030-2039. Our optimization is able to find a robust compromise policy that balances the system’s conflicting objectives well both now and in the future. We close by exploring how this policy coordinates operations across system reservoirs, which could inform reservoir operators in the CRB about how to adapt operations as the system changes in the future.