New Research Finds 472 Million People Worldwide Have Potentially Been Affected by Dams

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First Ever Global Analysis Examines How Dams Have Impaired Food Security and Livelihoods, Offers Pragmatic Solutions for Mitigating Dam Impacts

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At a time when global dam-building is rampant, we need to be smarter about planning for and operating dams in ways that alleviate harmful human and ecological impacts.

Today, The Nature Conservancy and partners released a new report calling attention to the large number of river-dependent people that have been affected by dams around the globe. Published in a special issue of the Water Alternatives journal recognizing the 10th anniversary of the World Commission on Dams, the findings reveal that at least 472 million people have potentially experienced negative consequences to their incomes and livelihoods.

“There are many places where dams have undeniably provided economic benefits such as flood protection, irrigation, and hydropower, but as this report shows they have also caused serious consequences for some of the world’s most vulnerable people,” said Brian Richter, The Nature Conservancy’s Global Freshwater Program Director and lead author of the report. “At a time when global dam-building is rampant, we need to be smarter about planning for and operating dams in ways that alleviate harmful human and ecological impacts.”

While previous studies have focused on the number of people displaced by dam building projects, this paper, “Lost in Development’s Shadow: The Downstream Human Consequences of Dams,” provides the first ever analysis of the populations located downstream of dams whose livelihoods have been adversely affected by dam-induced changes in river systems. These changes can include altering the natural patterns of water flow, blocking movement of fish trying to reach spawning and feeding areas, and damaging human livelihoods such as fisheries, flood–recession agriculture, or floodplain grazing. Alterations in a river’s natural rhythm can and frequently do cause lifecycles and natural processes to break down, hurting not just the environment and species but also human communities and economies.

To calculate the number of potentially affected people, the report’s authors created a database documenting dam effects on people living along more than 120 rivers in 70 countries, and used geospatial analysis and case-studies to examine the populations located downstream of the world’s 7,000 largest dams.
Findings from the database include:

  •     Globally, a total of 472 million people living along dam-affected rivers have potentially experienced impacts to their fishing and other river-dependent activities.
  •     91 million of these people live along rivers that have been “most severely” impacted by dams.
  •     On the Kafue River in Zambia, 50 percent of the fish catch once consisted of the commercially-important three spotted tilapia, but after the Kafue Gorge and Itezhitezhi Dams were built, this figure was reduced to only 3 percent.
  •     On the Senegal River flowing through Mali and Senegal, fish catches before the Manantali and Diama Dams averaged 23,500 tons per year; after the dams were built, the fish catch was reduced by 50 percent.
  •     Asia clearly emerges as the epicenter of dam impacts; more than half of the world’s population and more than half of all large dams built to date can be found in this region, specifically in China, India, and Southeast Asia.
  •     In the Lower Mekong River, which spans Cambodia, Thailand, Laos and Vietnam, 40 million people are dependent on river and floodplain fisheries. In the Sunderban Delta in Bangladesh, 73 percent of all households are involved in floodplain fisheries.
  •     In the Mun River in Thailand, the Pak Mun Dam has caused a 60-80 percent decrease in fish catch, and 50 fish species have disappeared entirely.

While the economic benefits of riverine and floodplain fisheries can be difficult to calculate across impoverished, vast, and politically sensitive regions, the few studies that have been conducted suggest that the economic value of healthy, free-flowing river systems can be substantial and that their omission from dam planning can cause significant negative impacts to downstream communities. The paper’s authors point out that pragmatic, scientifically-sound and well-demonstrated approaches and solutions are already available and can be utilized today, not only at the dam planning phase but also retroactively, to adjust the operations of an existing dam.
"It is unacceptable that half a billion people have been essentially ignored," said Thayer Scudder, Ph.D., Professor of Anthropology Emeritus, California Institute of Technology. "At least that many have seen their lives adversely affected by large dams that were planned and built without sufficient concern for those living downstream. If the full scope of potential economic and personal costs of proposed new dams were calculated, fewer would be built."

The authors point to the example of the Penobscot River in Maine as a successful model to be replicated on a widespread scale. In the case of the Penobscot, scientists and dam managers are implementing solutions that produce hydroelectricity and enhance local development without destroying fisheries or flood-dependent crops.

Among the solutions outlined in the paper:

  •     Dam planning needs to occur at a river-basin scale, to ensure that interactions between the environment, economic development, and people dependent on the river are all evaluated, and that the people with an interest in the river’s health or development are all consulted. Planning at the river-basin scale can help direct dams away from the most sensitive or vulnerable areas.
  •     Dam engineers need to incorporate design features that protect ecosystems, such as ensuring that a dam will release adequate water downstream to sustain river species, especially during natural flood seasons, which are often breeding, migration and germination periods for species.
  •     To alleviate the downstream impacts of dams, additional health programs and local economic opportunities should be integrated into dam development projects to help raise living standards of rural communities.

Contributors to “Lost in Development’s Shadow: The Downstream Consequences of Dams” include The Nature Conservancy, the Global Water Policy Project, the California Institute of Technology, McGill University, and the University of Virginia’s Department of Landscape Architecture. The full report can be downloaded here:


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