Exploring the Implications
of Global Warming

Global warming of the earth's atmosphere will significantly affect all living things that depend on water for survival - humans, plants, animals, and fish. Scientists at Battelle-managed Pacific Northwest National Laboratory (PNNL) have developed models to estimate the impact of global warming on water resources in the western United States, where managers are looking toward scientifically based solutions to address increased demands on their agencies. "Our modeling techniques can help them make better decisions by illuminating potential tradeoffs between cost and risk," said Mark Wigmosta, chief scientist with PNNL's hydrology group. These researchers have developed a modeling system that links diverse but related models. "We were one of the first to link regional climate models with distributed watershed models and are now the leader in carrying that linkage all the way through fisheries habitat," Wigmosta said.

Applying the models to the Yakima River Basin in Washington State, scientists created a historic climate simulation based on observed carbon dioxide emissions from fossil fuel combustion, and compared the results with three future climate simulations based on likely increases in global population, economic growth, and energy production. All three simulations indicated that there would be more rain than snow in fall and winter, causing increased winter runoff and decreased winter snowpack. "We'll see a major shift in timing of runoff due primarily to an increase in air temperature," Wigmosta said. More precipitation as rain in fall and winter would mean a decrease of natural water storage in the snowpack, and less winter snowpack would lead to an earlier runoff, with water levels peaking as early as March, rather than May as in past years.

This change may significantly impact fish populations in the Yakima River. For example, adult fall Chinook begin their upstream migration in the autumn. The resulting salmon smolt migrate downstream the following spring, but under future climate scenarios, stream temperature remains high later in the fall, which may delay upstream migration of adult salmon. In addition, if spring snowmelt occurs more than a month earlier than in the past, time available for spawning, incubation, and rearing of smolt before they migrate downstream is further compressed. Other fish species, even other Chinook salmon runs, will be impacted differently.

Storing increased runoff in the fall and winter and releasing it during the time of the historical spring snowmelt may be one approach to solving this problem. However, as water resource managers consider changes in operating procedures, they must also consider other, often conflicting, water uses such as irrigation. "We believe the research we're doing will help water resource managers make increasingly difficult decisions about how to use water resources in the future," Wigmosta said.

For additional information, please contact Mark Wigmosta, 509-372-6238, mark.wigmosta@pnl.gov or Joe Devary, 509-376-8345, joe.devary@pnl.gov.