The Albedo-Climate Penalty of Hydropower

Abstract:

The establishment of hydropower reservoirs results in a decrease of surface albedo, the darker water surface being enlarged at the expense of brighter terrestrial surface cover. The associated positive radiative forcing offsets part of the negative radiative forcing resulting from the displacement of fossil fuels by hydroelectricity generation. Here we show, by quantifying the difference in remotely sensed albedo between globally distributed hydropower reservoirs and their surrounding landscape, that 45 % of all investigated hydropower plants required less than 4 years for the negative radiative forcing from the fossil fuel displacement to offset the positive radiative forcing resulting from the albedo difference. However, these break-even times exceeded 30 years in 16 % and 80 years, considered the lifetime of hydropower plants, in 7 % of all cases and are shown to depend on the specific combination of climatic (incident solar radiation) and environmental (magnitude of albedo difference) conditions and the power plant design characteristics (electricity generation to reservoir surface area). Given that efforts towards limiting global warming to below 1.5°C imply relatively short time scales, we conclude that future hydropower plants need to minimize the albedo penalty in order to make a meaningful contribution to these targets and avoid a no-win situation for climate and environment.