What is a dam?
The International Commission on Large Dams (ICOLD) defines a large dam as being over 15 m high. The definition also includes dams between 5-15 m high with a reservoir exceeding 3 million m3.
Dam facts and figures
© International Journal of Hydropower and Dams
The world's largest dam building nations, as highlighted in WWF's report To Dam or Not to Dam. (click here to enlarge image)
How many dams are there?
- There are as many as 48,000 dams over 15m high worldwide. About half of these are in China.[1]
- The aggregate storage capacity of all the dams worldwide is about 6,000 km3.[2]
How many new dams are being built?
- Another 1,600 large dams are under construction worldwide in an industry whose annual turnover is estimated at $50 billion or more.[1]
- Together, China, Turkey, Iran, and Japan accounted for 67% of the total number of dams under construction worldwide in 2003.[2]
What do dams do?
- Large dams generate 19% of the world's total electricity supply. One-third of the countries in the world rely on hydropower for more than half their electricity supply.[1]
- Half the world's large dams were built exclusively or primarily for irrigation. Some 30-40% of the 271 million hectares irrigated worldwide rely on dams.[1]
What are dams’ impacts?
- Of the world's 227 largest rivers, 60% are severely fragmented by dams, diversions, and canals, leading to the degradation of ecosystems.[3]
- An estimated 40-80 million people have been displaced from their homes by dam construction.[1]
How much do dams cost?
- The annual expenditure on large dams during the 1990s was between $32 and $46 billion. Throughout the twentieth century some $2 trillion was spent on dams.[1]
Sources:
1: The World Commission on Dams
2: The International Commission on Large Dams
3: WWF Report. Rivers at Risk: Dams and the Future of Freshwater