The formation of these cold pools is most pronounced during clear, calm weather. Since the zone of high pressure that provides California with many clear, calm days is projected to shift northward in a warming climate, the Pacific Northwest may see an increase in cold air pooling in many mountain valleys. This could lead to amplified warming on the ridges of several degrees, compared to that in the valleys.
Ecological and hydrological impacts are likely, but difficult to predict. Douglas-fir forests tolerate a wide range of temperature conditions and are fairly resilient, Daly said, but some plant or animal species that can't readily move may face challenges.
Cool valley bottoms with more stable temperatures could actually act as refuges from the hotter ridge tops for some species, but are not expected to escape the overall warming that will affect the region. Variations in snowmelt between ridge tops and valleys are also likely to become more complex.
"At a larger scale, these changes in regional airflow patterns may also alter the flow of marine air from the Pacific Ocean that helps cool and ventilate the interior valleys during summer," Daly said. "If there are more times when that ocean air flow pattern shuts down, the valleys where most of the population lives could become much hotter than expected."
Similar forces could be found in many Mediterranean climates around the world, such as in Europe, South America and parts of the western U.S., which have climates that are controlled by the seasonal movement of high pressure belts, Daly said.
"There is more we need to be concerned about than overall warming, and we really haven't given these localized issues much consideration," he said.
Research will continue in the Andrews Forest to study these changes as they evolve, scient
|Contact: Chris Daly|
Oregon State University