A forecast for the American West: hot and hotter
Over the summer and on into the fall, images of flames, smoke plumes, firefighting teams and ruined homes have been on replay, and with good reason: As of Aug. 31, this year tied the record for total acreage burned by wildfires, according to the National Interagency Fire Center. More than 8.4 million acres have burned to date — an area larger than the state of Maryland up in flames.
But as intense as the wildfires have been this year, they provide just a glimpse of the future of the American West.
In a new study, my colleagues and I analyzed more than four decades of fire data from the U.S. Forest Service. We found a clear long-term trend toward more and larger fires in 11 Western states.
On average, there are now more than 100 “large” fires (fires that consume at least 1,000 acres) each year on Forest Service land. In the 1970s there were fewer than 50. Compared with an average year in the 1970s, each year during the last decade saw seven times more fires that burned more than 10,000 acres, and five times more fires larger than 25,000 acres.
Many factors help drive wildfires, including land-use practices such as logging and fire suppression, day-to-day weather variability and insect and pest infestations. And humans remain the No. 1 reason fires ignite in the first place. But as temperatures have dramatically increased in the Western U.S., wildfires have gotten more frequent and more intense.
And temperatures in the West have climbed faster than in the rest of the country. In the Southwest and Rocky Mountain states, for example, average summer temperatures have risen by 1.6 degrees since 1970, according to our analysis. Scientists aren’t yet able to say how much climate change has influenced temperature change in the West, but the warming is consistent with changes across North America that have been linked to higher levels of greenhouse gases in the atmosphere. Climate models also show that in the coming decades, temperatures in the Western U.S. will probably keep rising.
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The National Research Council recently reported that for every degree Celsius (1.8 degrees Fahrenheit) in temperature rise, the size of the area burned in the Western U.S. could quadruple. Consistent with the council’s findings and previous studies, our research shows that the years with more large fires typically had higher-than-average spring and summer temperatures.
In recent decades, spring has become longer and warmer, and the snowpack has melted one to four weeks earlier than it did 50 years ago across the West, according to the U.S. Geological Survey. Higher temperatures and earlier snowmelt in turn can increase the volume of dry trees and brush available to ignite and burn, particularly at higher elevations. Not surprisingly, our analysis reveals a clear trend over the last 40 years where wildfires start earlier and burn later in the year, effectively stretching the “burn season” by 75 days, an additional 2 1/2 months of wildfires each year.
These trends are particularly startling for certain states. Since the 1970s, the average number of fires larger than 1,000 acres in a year has nearly quadrupled in Arizona and Idaho and has doubled in every other Western state, from the Rockies to the West Coast, except Washington.
This year, New Mexico endured the largest recorded wildfire in that state’s history. Colorado sustained more than half a billion dollars in 2012 wildfire-related damages . Eight firefighters have lost their lives this year trying to protect homes and the public lands that provide jobs and recreation for millions of Americans in the West.
Limiting wildfires must be a top priority for those of us who call the West home. Developing effective plans and tools to do that, however, means recognizing how climate change is working against us, and that it will probably make the record-breaking fires of 2012 a normal Western summer in the not-too-distant future.
Alyson Kenward is a scientist and analyst at Climate Central, which sponsored the study on Forest Service fire data in the West.
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