Greenhouse Gases from Reservoirs Fuel Climate Change

Hydropower reservoirs are considered to be major sources of low-carbon electricity that can be used to cut greenhouse gas emissions to combat climate change. But those same reservoirs emit global warming gases, and a team of researchers has now tallied just how much those gases impact the climate.

Globally, reservoirs are responsible for about 1.3 percent of the world’s man-made greenhouse gas emissions each year, or about the same as Canada’s total emissions, according to a study to be published in the journal Bioscience next week.  The findings come from a team of researchers led by Washington State University-Vancouver and the Environmental Protection Agency.

That emissions estimate may not sound like much, but the study says reservoir emissions can contribute significantly to carbon budgets countries use to meet their climate goals.  Reservoirs emit mostly methane, a greenhouse gas about 35 times as potent as carbon dioxide in its potential to warm the atmosphere over the course of a century.

Knowing how reservoirs contribute to global warming is critical because there is a dam-building boom occurring worldwide.  Previous research shows that about 3,700 major hydropower dams were planned or under construction globally as of 2014 as countries scramble to generate renewable energy and find new ways to store water during drought.

“To put these reservoir methane emissions in context, they are similar in size to other major human sources such as biomass burning and rice paddies, hence reservoirs are not necessarily the ‘clean’ energy source they are often thought to be,” the study’s lead authors, Washington State University-Vancouver Ph.D. student Bridget Deemer and environmental sciences professor John Harrison, said in an email.

The study’s greenhouse gas estimates include reservoirs built for all uses, including hydropower, drinking water, farm irrigation, and flood control, among others. 
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Kevin Trenberth, senior scientist at the National Center for Atmospheric Research, said the benefits of building reservoirs in an era of climate change can outweigh the impact of their methane emissions.

“Building reservoirs is essential if we are to manage water — to save the water from the heavier rains that occur for the longer dry spells that are also expected,” Trenberth said. “Water management is a huge issue and this study deals with only a tiny part.”

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