A delicate balance: Hydropower and salmon in a changing climate

Written by Marion Davis

Tuesday, 23 August 2011 22:50

Spring-run Chinook salmon are an endangered species, with populations in Central California down to about 16,000 fish. FLICKR/U.S. Fish & Wildlife Service, Pacific Southwest Region

Rising water temperatures threaten the survival of California’s spring-run Chinook salmon, and reducing hydropower production may be the only way to save them.

Wild Pacific salmon populations in California, Oregon, and Washington have been declining for many years, stressed by overfishing, changes in ocean conditions, water quality and habitat degradation, genetic mixing with hatchery stocks, and the damming of rivers.

Spring-run Chinook salmon (Oncorhynchus tshawytscha), which used to be plentiful in California’s Central Valley, are now an endangered species, down from about a million fish to only about 16,000, and limited to a handful of watersheds. And because adults over-summer in freshwater streams before spawning in the fall, they are greatly threatened by climate change.

On Monday, at World Water Week 2011 in Stockholm, SEI-U.S. researcher Marisa Escobar explained how hydropower generation might have to be adjusted to save Chinook salmon, drawing on a case study for Butte Creek, Calif. Her presentation was part of the seminar “Water and Climate in Focus: Enabling Effective Action: Adaptation across Political, Social, and Institutional Boundaries.”

More than 150 dams in California are set to be relicensed in the next decade, Escobar noted, and the conditions placed on those dams could make a difference between survival and extinction.

Quantifying the threat
The Butte Creek study, conducted by Escobar with SEI-U.S. Water Group director David Purkey and colleagues at the University of California–Davis, used SEI’s WEAP (Water Evaluation And Planning) system as well as SALMOD, a specialised salmon population modeling system, to look at how climate change would affect salmon runs.

Without changes in water management, they concluded, the water in the streams will become too warm, and Chinook salmon will likely go extinct in Butte Creek and all of California.

Butte-Creek-MarisaThe study also looked at possible adjustments to hydropower operations to protect the fish: halting the diversion of water from Butte Creek at one major dam during the critical July-September holding period, strategically releasing water from a reservoir, or doing both. They found that halting water diversions could significantly improve the salmon’s survival chances, but at the expense of large amounts of power generation.

“While the physical and environmental regulatory context in Butte Creek is unique, the kinds of tradeoffs between different water management objectives explored here are universal,” says Escobar. “Climate change will exacerbate the situation and make the search for innovation and compromise more challenging, so analyses like this, connecting WEAP to climate and ecosystem assessment tools, will be very valuable.”

Download a copy of Marisa Escobar’s PowerPoint presentation (PDF, 655kb), or read a Q&A with David Purkey about lessons from the Butte Creek project.