Multi-scale impacts of climate change on hydropower for long-term water-energy planning in the contiguous United States

Climate change impacts on watersheds can potentially exacerbate water scarcity issues where water serves multiple purposes, including hydropower. The long-term management of water and energy resources is still mostly approached in a siloed manner at different basins or watersheds, failing to consider the potential impacts that may concurrently affect many regions at once. There is a need for a large-scale hydropower modeling framework that can examine climate impacts across ajoining river basins and balancing authorities (BAs) and provide an assessment at regional to national scales. Expanding from our prior assessment only for the U.S. federal hydropower plants, we enhance and extent two regional hydropower models to cover over 85% of the total hydropower nameplate capacity and present the first contiguous U.S. (CONUS)-wide assessment of future hydropower production under CMIP6’s high-end SSP5-8.5 emission scenario using an uncertainty-aware multi-model ensemble approach. We present regional hydropower projections, using both BA regions and U,S. hydrologic Subregions (HUC4s) to consistently inform the energy and water communities for two future periods – the near-term (2020–2039) and the mid-term (2040–2059) relative to a historical baseline period (1980–2019). We find that the median projected changes in annual hydropower generation are typically positive – approximately 5% in the near-term, and 10% in the mid-term. However, since the risk of regional droughts is also projected to increase, the study suggests the potential for severe hydropower reductions that could be overlooked due to the increase in ensemble median hydropower generation. The assessment can inform regional utilities and power system operators in developing drought scenarios in support of designing long-term duration storage and evaluating the reliability of their energy infrastructure under inter-annual and seasonal variability in hydropower, with consistent projections at relevant scale for water managers to evaluate water-energy tradeoffs.