The implications of future climate change on the blue water footprint of hydropower in the contiguous US*

As the largest renewable energy source, hydropower is essential to the sustainability of the global energy market. However, a considerable amount of water can be lost in the form of evaporation from the associated multipurpose reservoirs, and hence enlarge the blue water footprint (BWF) of hydropower in a warming climate. To facilitate the sustainable management of both water and energy resources under the impact of climate change in the contiguous United States (CONUS), the BWF values of 143 major multipurpose reservoirs were evaluated during the historical period (1985-2014) and two future periods (2020-2049 and 2070-2099). The historical reservoir evaporation loss was calculated using the Landsat-based reservoir surface area and a new evaporation rate algorithm that considers the heat storage effect. Future projections of runoff availability, hydropower generation, and reservoir evaporation were estimated based on the downscaled climate model ensemble from phase 5 of the Coupled Model Intercomparison Project. It was found that the BWF for the CONUS is highly spatially heterogeneous, with an average value of 26.2 m(3) MWh(-1) in the historical period. In the future, the BWF values are projected to increase under both Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios. This is especially noticeable under RCP 8.5, which has an average BWF value of 30.2 m(3) MWh(-1) for 2070-2099 (increasing by 15.3% from 26.2 m(3) MWh(-1)). The uncertainty ranges increase even more, from 3.4 m(3) MWh(-1) during 2020-2049 to 5.7 m(3) MWh(-1) during 2070-2099. These findings can benefit water and energy resources management in identifying suitable environmental, economic, operational, and investment strategies for multipurpose reservoirs in a changing environment.