Despite this year's record snowfall in the Pacific Northwest, the amount of water stored as mountain snowpack is projected to drop significantly in the long run, a change that could repaint the face of the region and drastically alter how water is used and allocated, according to University of Washington researchers.
Ocean/atmosphere models, which predict rising temperatures globally, tend to move the snowline in the Pacific Northwest to higher elevations over time, said Dennis Lettenmaier, a professor of civil and environmental engineering at UW. As a result, more precipitation falls as rain at lower elevations and less is stored for summer when it's needed.
According to modeling studies, water stored as snow is projected to decline 23 to 30 percent by 2025. The models indicate a drop of as much as 51 percent by 2055, and 61 percent by 2095.
"That's a lot of water that's not being stored in the mountains," Lettenmaier said. "And that water is what drives all the hydrology and the water resource management concerns. It is a serious issue."
Lettenmaier and UW research engineer Alan F. Hamlet are presenting their findings this week during the spring meeting of the American Geophysical Union in Boston. The research will be discussed during a poster presentation at 1:30 p.m. June 4 in Hall A/B. Also on June 4, Lettenmaier will take part in a news conference on the U.S. National Assessment on the Potential Consequences of Climate Variability and Change project.
As a starting point for their research, Lettenmaier and Hamlet used several models developed for the U.S. national assessment by climate-modeling centers to predict climate change on a global level. Some of the models foresee wetter conditions, others drier, but all indicate an increase in temperatures worldwide, Lettenmaier said.
Information from the large-scale climate simulations was plugged into existing historical precipitation and temperature data sets. Those data sets were then used to drive a hydrology model for the Columbia River Basin. Simulations of natural streamflow from that model in turn were used to drive another model that simulates reservoir operations at the major dams in the basin. The results - reduced snowpack and lower summer streamflow - highlight a number of thorny issues for the region. Water storage is one.
"If you lose the snow storage, you need storage from somewhere else," Lettenmaier said. "But from an environmental standpoint, no one is ready to run out and build more dams."
The boundaries between grasslands and forests could shift, which could affect the animals that live in those habitats. The projected changes could also have an impact on fisheries, hydroelectric power generation and recreational activities.
Given this year's record snowfall in the Pacific Northwest, the findings may seem contradictory to some, Lettenmaier said. That actually underlines an as yet largely unexplored aspect of the issue: the role that natural climate variations, such as the El Niño Southern Oscillation and the more recently documented Pacific Decadal Oscillation, play in influencing climate change on a regional level.
"You look at this stuff and say, 'See, the sky is falling,'" Lettenmaier said. "Then someone says, 'But didn't Mt. Baker just set a snowfall record?' It's hard to understand at the regional scale. What we may see is that these changes are susceptible to being masked by natural variability, at least in the near term."
For more information, Lettenmaier can be contacted through June 2 at the University of Washington at 206-543-2532 or at dennisl@u.washington.edu. After June 2, he can be reached in Boston through the AGU pressroom at 617-954-3094.