At some stations, stored water absorbs enough sunlight to offset the station’s carbon savings.
A hydropower station’s dark reservoir can soak up enough solar energy to cancel its climate benefit.
More than 3,700 major hydropower stations are planned or are under construction, and could bolster the world’s supply of low-carbon electricity. But hydropower requires storing large volumes of water, and a hydropower reservoir often absorbs more incoming solar energy than the terrain it replaced.
Georg Wohlfahrt at the University of Innsbruck, Austria, and his colleagues analysed satellite data at 724 hydropower stations around the world and found that the reservoirs were darker than the surrounding landscape and thus absorbed more solar energy. The team then calculated the extra warming from each reservoir as well as the warming that would be avoided at each by generating electricity from hydropower rather than fossil fuels.
The team found that nearly half of the stations produced net climate benefits within four years. But 19% needed more than 40 years to produce such a benefit, and 12% of stations failed to do so within their estimated 80-year lifetime. The authors suggest that reservoir design should account for reflectance changes.