Energy and water systems in the Western US (WUS) are closely connected, with hydropower comprising up to 80% of generation, and electricity to pump, treat, transport, use, and heat water comprising up to 20% of electricity use in certain states. Climate change presents a serious threat to WUS water resources, and because of these energy system interdependencies, is likely to have feedback effects on electricity demand and generation. In order to capture these water-energy dynamics and quantify cross-sectoral vulnerabilities under climate change there is therefore a need for a model that 1) represents and links physical hydrology with water management, 2) estimates climate impacts on both water availability and demand, 3) tracks subsequent hydropower and energy use of the water system, and 4) covers the widespread regional connections of both water and electricity networks.

Addressing these gaps, we develop a climatically-driven physical hydrology and water management system model of the WUS with the Water Evaluation and Planning (WEAP) platform. In addition to characterizing water sector dynamics (watershed hydrology, groundwater, water demand, water supply, and water infrastructure), the model includes 200 hydropower generators with installed capacity greater than 30 MW and calculates the energy use for water, which together can be linked with an electricity system expansion tool to support climate-resilient grid planning. We first calibrate the model with historical climate data to represent observed hydrology, water allocations, and energy use and generation, and then apply the model to an ensemble of 15 climate scenarios out to 2050.

The climate ensemble results show decreasing streamflows in key WUS basins, especially the Colorado. Electricity use for water also increases, driven by higher agricultural demand and shifts to more energy-intensive groundwater to replace declining surface water. Hydropower varies regionally with precipitation, but total WUS generation declines annually and peaks earlier in most cases. With energy use increases concurrent with hydropower generation declines, these findings suggest that climate impacts on the water system will add to energy system risks, and confirm the model’s value in evaluating the climate signal on both water-for-energy and energy-for-water.