Dams are one of the most pervasive human modifications of the planet, dating to at least the fourth century B.C.E. They are built to improve navigation, control flooding, irrigate crops, provide water for people and industry, and most recently generate electricity. The Global Dam Watch database catalogs more than 40,00 dams in all continents except Antarctica, including thousands of hydroelectric plants with a capacity of more than 1 megawatt (MW).1 There are tens of thousands of additional smaller dams.
The world’s first hydroelectric project was used to power a single lamp in the Cragside countryhouse in Northumberland, England, in 1878. The first plant to serve a system of private and commercial customers was opened in Appleton, Wisconsin in 1882 with an output of about 12.5 kilowatts. Within a decade hundreds of hydropower plants were in operation.2 The construction of new hydroelectric plants accelerated after World War II, initially in the United States and Canada, but then rapidly spreading to other parts of the world.
In 2023, there were about 2600 operating hydroelectric plants in the world with a capacity of at least 75 MW.3 Those facilities had a combined nameplate capacity of about 1.1 TW hours, equivalent to about 14% of the world’s entire electric generation capacity. China accounts for 29% of the world’s installed hydroelectric capacity, followed by Brazil, the United States, and Canada.
In the recent past, the dynamics of hydropower capacity additions have been shaped by mega projects. In China, the Baihetan (16,000 MW) and Three Gorges Dam (22,500 MW) projects anchored the country’s six-fold increase in hydroelectric generating capacity from 2000 to 2023. Similarly, the 14,000 MW Itaipu hydroelectric plant in Brazil and Paraguay by itself increased capacity in the region by 67% when it commenced operation in 1984.
There are more than 1000 large hydroelectric projects in the world in various stages of planning, preconstruction, and construction. The low cost and low carbon benefits of electricity from hydropower must be balanced with the significant impacts of large projects. Dams and reservoirs disturb riparian ecosystems, dislocate marginalized populations, and induce seismic activity. Research indicates that methane emissions from reservoirs are significant and somewhat diminish hydropower’s climate benefit relative to conventional wisdom.4 Rigorous environmental assessments and inclusive decision-making are necessary to mitigate these impacts.
1 Zhang, A.T., Gu, V.X. “Global Dam Tracker: A database of more than 35,000 dams with location, catchment, and attribute information.” Sci Data 10, 111 (2023). https://doi.org/10.1038/s41597-023-02008-2
2 International Hydropower Association, “A brief history of hydropower,” https://www.hydropower.org/iha/discover-history-of-hydropower
3 Global Energy Monitor, “Global Hydropower Tracker,” May 2023 release, https://globalenergymonitor.org/projects/global-hydropower-tracker/
4 Mingxu Li, Nianpeng He, “Carbon intensity of global existing and future hydropower reservoirs,” Renewable and Sustainable Energy Reviews, Volume 162, 2022, 112433, https://doi.org/10.1016/j.rser.2022.112433