Massive Wallow Blaze Incinerates Ariz. Forests, but Climate Change Link Remains Unknown

Massive Wallow Blaze Incinerates Ariz. Forests, but Climate Change Link Remains Unknown

07 June 2011

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USA — Arizona’s third-largest forest fire in history was fostered by drought conditions tied to La Niña, strong winds and parched soils and vegetation. But experts say its role as an example of the consequences of climate change is tenuous.

The Wallow fire in Arizona’s Apache-Sitgreaves National Forest has spread throughout the south and west of Alpine, Ariz., incinerating close to 250,000 acres. It began on May 29, and authorities believe it was ignited by human activity. The cost of the damage to date is $7.7 million, with the number expected to rise. The nearby Horseshoe 2 fire in southeastern Arizona, which began on May 3, has caused an estimated $28 million in damages, despite being half the size of Wallow.

A strong La Niña pattern — when cooler Pacific Ocean temperatures cause dry spells in the Southwest and South and heavy rains in the northwestern United States — set the environment for violent wildfire activity, said Robyn Heffernan, a fire meteorologist with the National Weather Service. Strong winds also contributed to the rapid sweep of the Wallow fire, at one point engulfing almost 50,000 acres in 24 hours.

Strong winds are usually a factor in the Southwest and the Southern Plains, said Heffernan, but the combination with dry temperatures is what’s unusual.

“We’ve seen wind conditions that we typically see, with droughts that we don’t typically see,” she said.

Impacts of ‘extreme drought’ compounded by high winds

A lack of snowmelt in the region that restricted the amount of fuel moisture — the percentage of water in vegetation — is exacerbating the rate of spread, said Ed Delgado, program manager for predictive services at the Bureau of Land Management’s National Interagency Fire Center. But the biggest factor was the trough of low pressure that brought sweeping winds over two-thirds of the interior of the western United States.

Despite a slight upward trend in the extent of the fires, Wallow’s link to global climate change is subject to interpretation, said Delgado.

“Overall, we have seen a bit of an increase over the last decade or so,” he said. “Can we attribute it to one thing? I don’t think so.”

There are other factors, he added, like the management of urban interfaces and population growth, that play a role in the severity of forest fires.

The U.S. Drought Monitor has currently designated the drought level around Alpine as “extreme.” In May 2008, as the continent was emerging from a particularly strong La Niña, the same region was only mildly affected by drought.

Indeed, La Niña and its counterpart El Niño — which is characterized by warming temperatures on the Pacific’s surface water — can produce different impacts each year they occur, said David Brown, climate services director for the Southern Region of the U.S. National Oceanic and Atmospheric Administration.

More to come in the future?

“This La Niña event was exceptionally strong,” he said. “That difference made a much more intense drought impact, shifting a lot of winter storms out of Arizona.”

The reason for this variability in patterns is studied intensely, but a concrete cause has yet to emerge, added Brown.

“It’s of course one of the big questions,” he said. “But there’s no clear answer between climate change and climate areas like El Niño and La Niña.”

To ponder the fire’s relationship to climate change, said Anthony Westerling, a professor of environmental engineering and geography at the University of California, Merced, is the wrong question to ask because it is impossible to answer.

“We know that our climate is changing, and that in the future we expect to see more frequent drought and earlier spring in the Southwest,” said Westerling, whose research centers around assessing future scenarios for forest fires. “We can’t rerun our current climate experiment without human-caused changes to our climate system to know whether we would have experienced a La Niña with a drought like this or not.”

A better question to ask, said Westerling, is whether fire-ravaged systems will be able to sustain themselves if climate change continues.

“We do know that Mother Nature is now playing with loaded dice,” he said.

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