The electricity sector faces a dual challenge: decarbonization and adaptation to climate change. In many regions, this challenge is complicated by interdependence of electricity and water systems, through hydropower and energy-intensive water resources. By coupling detailed water and electricity system models, we evaluate how climate change alters pathways to carbon-free generation across the Western Interconnect, emphasizing water interactions.We find that grid planning ignoring climate projections and water linkages underestimates the capacity needed to achieve decarbonization and maintain grid reliability.  Here, we show that to adapt, the region would need to build up to 139 GW of capacity between 2030 and 2050, equivalent to nearly thrice California’s peak demand, and could incurup to $150 billion (7%) in additional costs.  We examine sensitivity of these findings across a range of 15 climate projections for the Western US, noting qualitatively distinct pathways to an optimal grid across the ensemble.  We also note that climate effects tend to compound within the summer months when higher electricity demands and reductions in hydropower supply are both concentrated.

Within the HyperFACETS project, this work also serves as a cases study for one of our co-produced cross-cutting themes.  Through our engagement with resource management practitioners and members of the MultiSector Dynamics research community, we have identified the use of climate information within a hierarchy of multiple sectoral models as a cross-cutting area requiring methodological innovation and expert guidance.  We have conducted a survey of public sector and research community practitioners to systematically understand current practices and common challenges that require fundamental science to address.  Here we also present the rationale and preliminary results from this engagement, showing how the water-energy modeling work serves as an example of common challenges faced by a broader community.