Monster wildfire in Arizona: A glimpse of what climate change could bring
Even as the Wallow fire threatens to alter the Arizona landscape for a long time to come, some scientists say climate change may be fueling a trend toward larger wildfires in the American West.
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As La Nina weakens, and the rainy season begins in the Southeast, forecasters at the National Oceanic and Atmospheric Administration's Climate Prediction Center say they see some easing of drought conditions in many regions along the southern tier – but in many cases not enough to erase the drought itself.Skip to next paragraph
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But the longer-term trend in large, longer-lasting fires looks to be driven at least in part by global warming, which most atmospheric scientists attribute to a build-up of carbon-dioxide in the atmosphere – released through burning fossil fuels and through land-use changes.
Researchers documented the change in a study published in 2006 – in the middle of a four-year period when wildfires consistently consumed more than 8 million acres a year in the US. The increase in larger fires began somewhat abruptly in the mid-1980s, according to the study, which analyzed fire, climate and hydrological data between 1970 and 2004.
"This jump means something more than just the fuels," says Swetnam, a member of the research team, referring to a buildup in scrub growth and brush in some terrain that has also fueled wildfires.
The increase in larger, longer-lasting fires was most pronounced in the northern Rockies and at high elevations.
"That argued more in favor of a climate effect than a Smokey Bear effect" in which humans have contributed to a buildup in fuels by interfering in natural fire cycles, he says. The climate change manifests itself as warmer temperatures and earlier springlike temperatures, which increases the likelihood of longer dry spells.
Subsequent work the team has done since then has reinforced the earlier study's conclusions, Swetnam says.
As a fire ecologist, he says he's keeping a close eye on Arizona's Wallow fire, which has torched more than 300,000 acres in northeastern Arizona. It stands to dramatically alter the landscape for some time to come, he says.
Fears for Ponderosa forests
Arizona's fires – especially the Wallow fire – are burning their way through Ponderosa Pine forests, and "from the tree-ring record, these events are very strange," Swetnam says.
They are creating extremely wide gaps in a forest whose trees do not respond as well to fires as did Yellowstone's lodgepole pines following a devastating fire there in 1988.
Ecologists were stunned at how quickly the forest began its recovery following that blaze, which scorched nearly 800,000 acres. Burnt Lodgepoles respond to fire by dropping their pine cones after a fire passes, allowing the seeds in the remaining pine cones to find fertile soil.
Pondserosa's don't do that, Swetnam explains. They produce seeds erratically and drop them right away, with long stretches of time between seed production, dramatically slowing the recovery of the forest.
Instead, vegetation in the burnt Ponderosa areas could well convert to wild grasslands and shrubs that could dominate the landscape for a long time to come, he says.
IN PICTURES: Arizona's Wallow fire