Global use of hydropower increased more than 5 percent between 2009 and 2010, says new research published last month by the Worldwatch Institute for its Vital Signs Online publication.

Hydropower use reached a record of about 3,400 terawatt-hours, or 16 percent of global electricity consumption, by the end of 2010, continuing the rapid rate of increase experienced between 2003 and 2009.

The cost of hydropower is relatively low, making it a competitive source of renewable electricity. The average cost of electricity from a hydro plant larger than 10 megawatts is 3 to 5 cents per kilowatt-hour. Hydropower is also a flexible source of electricity since plants can be ramped up and down quickly to adapt to changing energy demands.

Yet there are many negative aspects associated with hydropower: For example, damming interrupts the flow of rivers and can harm local ecosystems, and building large dams and reservoirs often involves displacing people and wildlife and requires significant amounts of carbon-intensive cement.

"In the future, hydropower is likely to continue to grow—despite the environmental challenges involved in expanding it—because of its competitive price and climate benefits, which make it an attractive option as countries seek to lower their greenhouse gas emissions," says report author Matt Lucky, a Worldwatch sustainable energy fellow.

China was the largest hydropower producer and is expected to continue to lead global hydro use in the coming years. The country produced 721 terawatt-hours in 2010, representing around 17 percent of domestic electricity use. China also had the highest installed hydropower capacity, with 213 gigawatts at the end of 2010. It added more hydro capacity than any other country, 16 gigawatts in 2010, and plans to add 140 gigawatts by 2015. This is equivalent to building about seven more dams the size of China's Three Gorges Dam, currently the largest in the world.

"While hydropower energy production helps reduce reliance on fossil fuels and avoids much of their carbon dioxide emissions, this form of electricity generation is rarely without social and environmental cost and risk," says Worldwatch President Robert Engelman. "Hydro-power is indeed low-carbon renewable energy, but new hydro development nonetheless needs to pass rigorous tests for its environmental and social impacts."

Hydropower is produced in at least 150 countries. The Asia-Pacific region generated roughly 32 percent of global hydropower in 2010. Africa produces the least hydropower, accounting for 3 percent of the world total, but is considered the region with the greatest potential for increased production.

In 2008, four countries—Albania, Bhutan, Lesotho, and Paraguay—generated all electricity from hydropower, and 15 countries generated at least 90 percent. Iceland, New Zealand, and Norway produce the most hydropower per capita.

Micro-hydropower, which is defined as a plant with an installed capacity of 100 kilowatt-hours or less, has grown in importance over the last decade and can be an effective means of providing electricity to communities far from industrial centers. As of 2009, roughly 60 gigawatts of small hydro was installed worldwide, accounting for less than 6 percent of the hydropower total. Small hydro is likely to expand, especially as populous countries continue to pursue rural electrification.

Five countries—China, Brazil, the U.S., Canada, and Russia—accounted for about 52 percent of the world's installed hydropower capacity in 2010.

There are now three hydropower plants larger than 10 gigawatts: the Three Gorges Dam in China, Itaipu Hydroelectricity Power Plant in Brazil, and Guri Dam in Venezuela.

A total of $40 billion to $45 billion was invested in large hydropower projects worldwide in 2010.