Indicators of thermal alteration in US waters reveal patterns of climate risk at the energy-water nexus

Anthropogenic changes in water temperature can pose significant risk to thermoelectric and hydroelectric generation. In this study, we developed indicators of thermal risk (ITRs) to assess risk to water-dependent electricity generating assets under future climate. We projected future changes in water temperature and quantified ITRs for plants across the conterminous US for a baseline and future period. One goal of our study was to tailor ITRs to measure climate risks mediated by aquatic biota. When using local species’ thermal tolerances as thresholds, we estimated that future conditions would expose an additional 53 GW or 30 % of once-through-cooled thermoelectric power (OTE) capacity and an additional 7.1 GW (10 %) of total hydropower capacity to slightly higher risk. Meanwhile, the future proportion of species exposed to risk increased by 25 % (OTE) and 15 % (hydropower). Because seasonal timing can be important when understanding competing demands for cold water, we developed two metrics of risk timing (median date of exceeding thermal thresholds and the duration of exceedances). Although changes were small (<5 d) for most plants, for some plants timing shifted by +/- five weeks and for others the duration of exceedances increased by 10 to 15 d. Geographically, elevated future risk was highest for plants in the southeastern US, reflecting future exposure to warming and the high aquatic biodiversity of rivers draining to the Gulf of Mexico and South Atlantic coast. We discuss how results from our ITR analysis can be used to plan climate-adaptation measures at both grid and plant scales.