Colorado wildfire frequency tied to ocean temperature patterns

Colorado wildfire frequency tied to ocean temperature patterns

9 October 2007

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El Niño vs. La Niña

The periodic shift between warmer-than-normal (El Niño) or cooler-than-normal (La Niña) water in the eastern Pacific is one of the biggest factors driving weather patterns, determining where storms track off the Pacific Ocean and across continental North America. The effect on Colorado’s winter weather is not as clear as in some other regions like the Pacific Northwest, where La Niña frequently results in above-normal precipitation.

SUMMIT COUNTY – For years, skiers have tuned in to long-range weather outlooks to determine whether an El Niño or La Niña might bring a bountiful powder season.

Along with shaping winter precipitation patterns, recent research suggests that the shifts in sea surface temperatures can also be tied to the frequency and intensity of forest fires.

For forests like Summit County’s subalpine lodgepole pines, drought conditions induced by La Niña, and even temperature shifts in the Atlantic Ocean, could be a bigger factor than previously thought.

After studying the historic recurrence of fire in Rocky Mountain National Park and comparing that data with climate records, Forest Service scientists concluded in a recent study that fire occurred more frequently than expected during La Niña conditions.

Another large-scale pattern that may be equally significant for Colorado is a change in Atlantic Ocean sea surface temperatures. The Atlantic multi-decadal oscillation, as it’s known, is not as understood as the Pacific El Niño/La Niña phenomenon. But the shift in temperatures does affect drought conditions in Colorado and other parts of the U.S.

Looking at climate and fire data going back to 1600, researchers found a statistically significant link between Atlantic ocean temperatures and wildfires in Western Colorado. In the subalpine zone – including Summit County’s lodgepole pine forests – fires occurred most frequently when an Atlantic warm phase coincided with La Niña conditions in the Pacific.

Because of a 1998 shift to a warming phase that could last decades, the Western U.S. could be looking a long-term period of higher fire danger, the scientists concluded in a report outlined in Intermountain West Climate Summary, published by the Wester Water Assessment project.

The wild card in all this is climate change, which, along with directly affecting temperatures in the West, could cause as-yet unkown shifts in oceanic temperature patterns.

The research could prove important for land managers as they try to asses the risk of wildfire associated with forests killed by pine beetles.

Some advocates of aggressive large-scale forest management have said that fire suppression has resulted in “unnatural” and “unhealthy” conditions in Colorado’s lodgepole pine zones, and that widespread logging is needed to restore a natural balance. Other studies suggests that drought and climate play a much bigger role in wildfire activity than logging, fire suppression and insect mortality.

Areas just to the west of Colorado, from northwestern Montana down through Idaho, Utah, Nevada and southwestern California are experiencing extreme drought conditions. A predicted La Niña for this winter probably won’t offer much relief for that area, although it suggests near average precipitation for Colorado.

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