Earth Notes
9:38 pm
Thu July 19, 2007

Climate Affects Arizona's Wildfires

Flagstaff, AZ – Almost everyone in Arizona has smelled the smoke and has felt a bit of a panic when fire season strikes close to home.

(Archive NPR newscast) From NPR news in Washington I'm Craig Windom. Fire crews in Arizona say they're running short of resources and time as they try to prevent two major wildfires from merging. If that happens

That's a newscast from five years ago just before the Rodeo and Chediski fires merged creating the largest wildfire in the state's history. The state's largest fires have burned in the last two decades. In 1990 the Dude Fire killed six firefighters near Payson. In 2003 the Aspen Fire destroyed hundreds of homes north of Tucson. Just last year the Warm Fire north of Grand Canyon smoked out hundreds of tourists.

In Peter Fule (fool-LAY)'s office at Northern Arizona University he pulls out a chart that shows many of those fires. Each circle on the diagram represents a fire.

FULE: The bigger the circle the bigger the fire. This is the rodeo chediski right here.

He's a forestry professor at NAU and helps direct the Ecological Restoration Institute. He says it's important to look at past fires to prepare for the future.

FULE: So as you move this way it gets hotter and you move this way it gets drier so here's the Rodeo Chediski in this hot dry corner. And what this arrow shows is the projection based on consensus of climate models of where climate might be expected to change in the coming decades and you'll notice that it's strongly warmer.

Recently a group of scientists gathered all of the data they could find on wildfires in the western United States. They analyzed location, timing and climate. They found the length of the wildfire season has increased by almost 80 days. And where fires used to burn for about a week they're now burning on average longer than a month. They attributed all of this to an increase in spring and summer temperatures along with earlier snow melt.

SWETNAM: With warmer temperatures and droughtier conditions there's likely to be additional large forest fires.

Tom Swetnam was one of the study's authors. He runs the tree ring lab at the University of Arizona. Rings from living trees can tell the history of the surrounding environment and past fires.

SWETNAM: So using the climate history from tree rings and fire history from tree rings we can see that climate variability has driven fire activities for many centuries even millennia.

Tom Swetnam and Julio Bentacourt, a hydrologist with the United States Geological Survey, just returned from a research trip across the southwest. Bentacourt says everywhere they went they saw trees dying off.

BENTACOURT: I mean there are huge areas of western forests that are experiencing tremendous die offs. That's an unusual glut of fuel. My feeling is the fuel dam is getting ready to break.

He says Smokey the Bear, grazing and forest management all play a role. In the past it was normal to put fires out as quickly as possible. That allowed forests to become extremely dense.

To make matters worse Bentacourt says the higher temperatures and the longer warm season make favorable conditions for insect outbreaks.

BENTACOURT: Before they would get only one generation going. Now you can have two generations of bark beetles attack pine forests. This is happening throughout western North America and it makes the fire situation that much worse.

Chuck Maxwell says you can't point to one culprit that's causing more intense wildfires. He's a predictive services meteorologist with the southwest coordination service in Albuquerque. He says Arizona's been in a drought since 1999.

MAXWELL: That has overpowered almost anything else with regard to any kind of climate change signal or anything else that's out there. There's always different cycles ongoing all the time. A 10 year drought cycle that has nothing to do with anything else can become the dominant player at a certain time. That's kind of where we've been the past 10 years. It just happens to be the same 10 years people have been much more aware of climate change. And people are wanting to point to the fire activity over the last 10 years as evidence of that and it may or may not have any relationship whatsoever.

Maxwell says droughts have lasted up to 50 years in the past so evidence must be studied over a long period of time before making any conclusions.

MAXWELL: You can take pictures of a glacier every 10 years and see it shrinking. It isn't quite as simple to look at the forests and ecosystem and see how that changes because it changes in different ways it's very dynamic.

Tree ring expert Tom Swetnam agrees there's a lot of uncertainty.

SWETNAM: I would be the first to acknowledge that we don't really know how much climate is going to change in the southwest particularly rainfall. Rainfall patterns are the least well predicted by the regional climate models ...but the trend arrows are not good the trends are toward increasing numbers of large fires and more fire on the landscape at the same time we have increasing population pressures and other changes occurring in our ecosystems.

Fire has always played a natural role in the ecosystem. But fires have also grown unnaturally big. Scientists aren't yet certain how much of that is because of a changing climate. They agree wildfires will likely continue to get bigger and more frequent.

For Arizona Public Radio I'm Laurel Morales.