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Damming last big rivers on Earth

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We’re damming up every last big river on Earth. Is that really a good idea?

Updated by Brad Plumer on October 28, 2014, 4:05 p.m. ET @bradplumer
brad@vox.com

The Three Gorges discharges water during a flood peak July 08, 2012 in Hubei, China. TPG/Getty Images

Solar and wind power get all the attention these days, but the global hydropower frenzy that’s currently underway could end up being just as consequential for the planet — for better or for worse. Hydropower can provide a source of renewable energy — but also wreak havoc on river habitats Hydroelectric dams are still the biggest source of renewable energy around, generating 16 percent of the world’s electricity. And, according to a recent study in Aquatic Sciences, more than 620 large hydroelectric dams are now under construction, largely in Latin America and Asia — with thousands more in various stages of planning. At the high end, if most of the planned dams were built, global hydropower production could double to 1,700 gigawatts, the study’s authors predict. This would also reduce the number of large free-flowing rivers on the planet by another 20 percent. There are upsides and downsides here. If built, these dams could provide electricity for millions of poor people who don’t have it. But dams can also be extremely controversial. Some projects can end up displacing thousands of people and destroying river habitats — something the United States learned the hard way last century. What’s more, recent research has questioned whether hydropower is always as climate-friendly as once thought…..

And what about global warming? In theory, hydroelectric dams should produce fewer greenhouse-gas emissions than, say, coal plants. But there’s a huge caveat here. Some recent research has suggested that decaying vegetation in stagnant dam reservoirs may end up producing lots of methane, another potent greenhouse gas. For many dams, this can actually offset a big chunk of the climate benefits, especially in tropical countries like Brazil. So hydropower isn’t always as green as it seems. (There are, however, ways to build lower-emitting dams — but it has to actually get done.)….

Obviously no one’s going to tear down the Hoover Dam, which still provides electricity for millions of people in Nevada, Arizona, and California. But many smaller dams are now getting dismantled — including the 108-foot Elwha River dam. (The hunt for carbon-free electricity, however, has complicated this task. Back in 2013, Congress passed a bill to help eke out more power from small rivers and streams, particularly by adding generating capacity to existing dams.) … Among other things, the US was providing aid to Cambodia to study how dam construction would affect the river’s flow. The latest Aquatic Sciences paper, by providing a comprehensive database of the 3,700 largest dams being contemplated, aims to provide a useful resources to planners hoping to address some of these concerns. “Clearly,” the authors note, “there is an urgent need to evaluate and to mitigate the social, economic, and ecological ramifications of the current boom in global dam construction.”

The worldwide dam-building frenzy

Global spatial distribution of future hydropower dams, either under construction (blue dots; 17%) or planned (red dots; 83%). Credit: Aquatic Sciences (DOI: 10.1007/s00027-014-0377-0)

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