Climate change could increase winter inversions

By 2100, mountaintops could warm by 14 degrees, says an OSU study

An Oregon State University research project suggests winter air inversions in Southern Oregon could intensify as the region's climate changes.

Researcher Chris Daly said Wednesday that Southern Oregon's winter inversions provided the inspiration for him to study how climate changes might affect local weather in steep mountainous terrain. He had noticed the wide winter temperature variations between Medford and Sexton Mountain, and he wanted to find out whether similar temperature differences could occur over much shorter distances.

To say that temperatures will increase, for example, 5 degrees on average over the next century doesn't mean every site will see the same amount of warming, he said.

"We are finding that the potential effects of climate change may be more complicated than we ever thought they would be," Daly said in a telephone interview.

A team of OSU researchers looked at temperature data from hill and valley sites at the H.J. Andrews Experimental Forest near Blue River, east of Eugene. They ran the data through computer models based on a 5 degree average temperature increase for Western Oregon by 2100 and concluded that some sites, such as mountain ridgetops, could warm by as much as 14 degrees at some times.

Temperatures in the cold-air pools in the valleys would likely increase closer to the predicted 5-degree average, he said.

The wide temperature variation could have major implications for plants and animals that inhabit those areas, Daly said. The findings also have meaning for Southern Oregon, where steep ridges and narrow valleys provide the topography for substantial inversions to develop across relatively small distances.

Daly is an OSU professor of geosciences and director of OSU's PRISM Climate Group. He said most computer models indicate Oregon could have more cold, clear winter days as the climate changes. Cold clear weather provides the conditions for inversions to develop, but there has been little research so far about how much weather will vary at specific sites.

The report is to be published by the International Journal of Climatology under the title "Local atmospheric decoupling in complex topography alters climate change impacts."

Reach reporter Bill Kettler at 541-776-4492, or e-mail

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