The electricity sector faces a dual challenge: decarbonization of generation and adaptation to changing resources and demands under climate change. In the semi-arid Western United States (WUS), this challenge is complicated by the interdependence of its electricity and water systems: hydropower comprises about 20% of generation, and electricity to pump, treat, and transport water comprises about 7% of electricity use. Climate change presents a serious threat to both surface water availability and water demand, and will likely have cascading impacts on hydropower generation and electricity use related to water, such as for groundwater pumping. Failing to account for these changes in energy supply and demand via the water sector may overlook compounding vulnerabilities, leading to generating capacity shortfalls that jeopardize grid resilience and make meeting decarbonization goals elusive.

We evaluate how climate change alters the pathway to decarbonize the electric generation portfolio of the Western Electricity Coordinating Council (WECC) grid region, with an emphasis on water sector feedbacks. We develop a physical hydrology and water management model of the WUS to estimate changes in hydropower generation and water-related electricity use, under an ensemble of 15 climate scenarios out to 2050. We also estimate the changes in building cooling loads under the climate scenarios. We link all of these changes in load and hydropower under the climate scenarios compared to a historical climate with a grid capacity expansion model of the WECC to optimize the buildout of generation and transmission and reach zero carbon emissions by 2050.

We find that decarbonization planning that ignores climate projections and water interactions underestimates the capacity and investment needed to maintain grid reliability. By 2050, the incremental increase in annual load due to climate change could be up to 3%, while hydropower generation could decrease by up to -21%. To adapt to these changes, the region will need to build up to 140 GW more capacity between 2030 and 2050, adding up to $150 billion, or 7% more, in costs. This suggests that in the worst-case, adapting to climate change could require building almost three times as much generating capacity as California’s current peak demand by 2050.