Hydropower and the challenge of climate change

Clean hydroelectric plants are meant to help the world fight global warming. But what happens when climate change clouds hydro’s own future?

The Hoover Dam was and is a marvel of engineering, a 700-foot wall of concrete holding back the Colorado River. Its 17 massive power turbines supply electricity for southern California and a chunk of the U.S. Southwest. But in the space of a year, the Hoover power plant will have essentially shrunk in half, from about 2,100 megawatts of generation capacity in early 2014 to about 1,200 megawatts this spring, all because of the impacts of drought caused by climate change.

Big hydroelectric projects like the Hoover Dam are slated to play a leading role in helping the world meet its need for increased supplies of electricity. Huge dam projects are underway in Brazil, Turkey, Ethiopia, the Tibetan Plateau, and Southeast Asia. And since hydropower generates clean energy — with no emissions of carbon dioxide — it is seen as a key player in the world’s bid to both power up and fight the emissions that cause climate change.

But climate change itself is threatening the viability of big hydro projects today and tomorrow. Shifting rainfall patterns and chronic droughts are shrinking river flows and draining lakes, leading to decreased power generation at hydroelectric facilities. California, in the midst of the worst drought in U.S. history, has seen hydroelectric generation shrink to about half its average level.

And looming effects of climate change, including melting glaciers, threaten to make hydroelectric plants an even iffier proposition in the future, especially in Asia. Sorting out just how to divvy up ever-dwindling supplies of water that feed competing needs like power generation and agriculture will stoke even more tension between countries such as Egypt and Ethiopia, or China and its dozen downstream neighbors.

“In some areas, climate change could really compromise the practicability of using hydropower as an energy source,” said David Michel, director of the Environmental Security Program at the Stimson Center. “It’s not a question of an apocalyptic, rivers-are-running-dry scenario, but the tradeoffs with other demands for water could call many projects into question.”

The impacts of climate change are already being felt in many parts of the world today, as Secretary of State John Kerry said in a speech last week. Brazil just slogged through a historic drought that emptied reservoirs to their lowest level of the century and brought water rationing to sprawling cities like Sao Paulo. For a country reliant on hydroelectricity for about 75 percent of its power, the lack of rainfall could lead directly to blackouts. And Brazil’s energy minister recently warned the water and power crisis could get worse.

Water levels in Lake Mead, behind Hoover Dam, are slipping perilously; power generation there has dropped 10 percent since 2001. The lack of rain in California has slashed hydro generation there and increased the state’s reliance on fossil fuels. New Zealand, which gets half its power from hydroelectricity, is reeling after a record drought. Russia’s Lake Baikal, the world’s largest freshwater lake, has the lowest water levels in three decades, straining nearby hydro projects.

But the real challenge for hydropower still lies ahead. Some regions, such as the U.S. Southwest, are preparing for a much drier future, which means there will be less water available to run turbines, water crops, and fill up city reservoirs. Researchers at the University of Wisconsin estimate that future droughts will cut the Colorado River’s hydro generation by up to one-fifth. The U.S. Bureau of Reclamation, which oversees the Hoover Dam, is rejigging some of the power plant’s turbines to try and keep operating in a drier world.

Brazil’s ambitious plans for the Belo Monte hydroelectric project could well be imperiled due to lower future water flows. “They may not be able to ever run that facility in such a way to generate enough power to get back their huge INVESTMENT,” Michel said.

Other Latin American countries that rely on hydropower, such as Ecuador and Colombia, are worried that climate change will dent their energy and environmental options in the future. Colombian researchers concluded that climate change will lower hydroelectric output, force more reliance on pricier fossil fuels, and increase the country’s greenhouse gas emissions. For Ecuador, falling rainfall in the Andes could force the country to import more electricity from its neighbors.

Likewise, countries in southern Africa are banking on dams on the Zambezi River to provide decades of clean electricity. But with climate change expected to cut into rainfall, experts fear the biggest hydro projects will struggle to work as designed; environmental group International Rivers warned the region is “moving toward the edge of a hydrological precipice.”

Rising temperatures are also gnawing away at glaciers, the ultimate source for many of the world’s biggest rivers and essentially the long-term powerpack for many of the world’s biggest hydroelectric projects. In the short term, that can actually be a boost for hydropower, because the melting sends more water downstream, giving countries the options to either produce more power or store water for future use.

But melting glaciers present their own problems, as well. There will be less meltwater available for those watersheds in future decades, which means lower stream flows — which translates into lower power generation potential or a pinch on other water uses, such as agriculture. A small decline in river flows due to glacial melt could have an outsized impact on power generation in the Tibetan Plateau, researchers have found.

Even in the short term, melting glaciers present a headache. Hundreds of glacial lakes in the Hindu Kush have formed in recent years, backstopped by icy moraines. When they burst, as several have, they can send a catastrophic torrent downstream, damaging dams, hydropower facilities, and farmland.

“India, Pakistan, Nepal, Bhutan, all have enormous hydropower capacity still waiting to be developed, so they could theoretically derive huge benefits. But they confront those potentially difficult decisions about how to manage and operate those facilities in the face of climate change,” Michel said.

To be sure, climate change will make some areas wetter. The Pacific Northwest and British Columbia will likely see a boost to hydroelectric generation in decades to come as the years get wetter. But in general, competing users for water within countries and among countries could well stoke tensions, especially in already unstable parts of the world.

Turkey’s huge bet on dams and hydropower, the Southeastern Anatolia Project, or GAP, is meant to bring electricity, jobs, and irrigation to an impoverished corner of the country. But a score of dams and hydroelectric facilities at the headwaters of the Tigris and Euphrates rivers will choke off water supplies to downstream neighbors such as Syria and Iraq, which have already been fighting the effects of years of drought. The Ataturk Dam, one of Turkey’s biggest, cut downstream flows in the Euphrates River by one-third; GAP’s last big dam, still under construction, will likely cut water flows in the Tigris River in Iraq by 50 percent. Those water fights are exacerbating already strained political tensions between Ankara and Baghdad.

Likewise, China’s big hydropower development appears to be curtailing water flows in the Mekong River and has downstream neighbors anxious, even ones like Laos who are building their own dams and making their own neighbors nervous. The battle between power generation, fishing, and agriculture that is already shaping up on the Lower Mekong will likely only intensify as water flows diminish in future decades high in the Tibetan Plateau.

That could be a source of perennial tension between neighbors who in many cases are already at odds. Or, in a best-case scenario, Michel says water stress could end up focusing minds and forcing countries to work together.

“In many cases, the prospect of these ramifications of climate change could encourage these countries along shared water systems to think harder about how to cooperate,” he said.