Declining snowpack could change Northwest

Models indicate that in either a wetter or drier climate — a source of debate among climate researchers — rising temperatures will result in a reduced snow pack and lower summer stream flow

June 7, 1999
Web posted at: 3:00 PM EDT

Mountain snowpack is projected to drop significantly in the Pacific Northwest over the next several decades and change the way the region's water is managed, according to University of Washington researchers.

Climate simulation models 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 the University of Washington. As a result, more precipitation falls as rain at lower elevations and less is stored for summer when it is 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," said Lettenmaier. "And that water is what drives all the hydrology and the water resource management concerns. It is a serious issue."

The results of the modeling studies indicate that in either a wetter or drier climate - a source of debate amongst climate researchers — rising temperatures will result in a reduced snowpack and lower summer stream flow.

"If you lose the snow storage, you need storage from somewhere else," said Lettenmaier. "But from an environmental standpoint, no one is ready to run out and build more dams."

The changes may result in a shift in the boundaries between grasslands and forests, 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, said Lettenmaier. 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.

"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."

Lettenmaier and his colleague Alan Hamlet presented their findings Friday at the spring meeting of the American Geophysical Union in Boston, Mass.

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