Dam facts and figures

The Juturnaíba Dam rel=
The Juturnaíba Dam
© WWF-Canon / Edward Parker
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.

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]
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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
 / ©: 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)
© International Journal of Hydropower and Dams

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