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The Age of Western Wildfires

Research Report by Climate Central

Report Summary

Screenshot from Climate Central's Interactive Wildfire Tracker. Click here to check it out. 

The 2012 wildfire season isn’t over yet, but already this year is shaping up to be the one of the worst on record in the American West. According to the National Interagency Fire Center, with nearly two months still to go in the fire season, the total area already burned this year is 30 percent more than in an average year, and fires have consumed more than 8.6 million acres, an area larger than the state of Maryland.

Annual number of wildfires greater than 1,000 acres on U.S. Forest Service Land has been increasing. Click image to enlarge.

Yet, what defines a “typical” wildfire year in the West is changing. In the past 40 years, rising spring and summer temperatures, along with shrinking winter snowpack, have increased the risk of wildfires in most parts of the West.

Studies show that continued climate change is going to make wildfires much more common in the coming decades.

The National Research Council reports that for every degree Celsius (1.8oF) of temperature increase, the size of the area burned in the Western U.S. could quadruple. According to the IPCC 4th Assessment Report, summer temperatures in western North America could increase between 3.6oF and 9oF by the middle of this century.

Key findings

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Our analysis of 42 years of U.S. Forest Service records for 11 Western states shows that:

The number of large and very large fires on Forest Service land is increasingly dramatically.  Compared to the average year in the 1970’s, in the past decade there were:

  • 7 times more fires greater than 10,000 acres each year
  • Nearly 5 times more fires larger than 25,000 acres each year
  • Twice as many fires over 1,000 acres each year, with an average of more than 100 per year from 2002 through 2011, compared with less than 50 during the 1970’s.

Wildfires larger than 10,000 acres are about  seven times more common now than they were 40 years ago on U.S. Forest Service Land. Click image to enlarge.

In some states the increase in wildfires is even more dramatic.  Since the 1970’s the average number of fires over 1,000 acres each year has nearly quadrupled in Arizona and Idaho, and has doubled in California, Colorado, Montana, New Mexico, Nevada, Oregon, Utah and Wyoming.

On average, wildfires burn twice as much land area each year as they did 40 years ago.  In the past decade, the average annual burn area on Forest Service land in the West has exceeded 2 million acres — more than all of Yellowstone National Park.

The burn season is two and a half months longer than 40 years ago.  Across the West, the first wildfires of the year are starting earlier and the last fires of the year are starting later, making typical fire years 75 days longer now than they were 40 years ago.

Average annual temperatures overlaid with number of fires. Click image to enlarge.

Rising spring and summer temperatures across the West appear to be correlated to the increasing size and numbers of wildfires. Spring and summer temperatures have increased more rapidly across this region than the rest of the country, in recent decades.  Since 1970, years with above-average spring and summer temperatures were typically years with the biggest wildfires.

Previous research reveals that climatic changes, including increasing temperatures and the earlier onset of spring snowmelt, have been linked to increasing levels of atmospheric greenhouse gases and are likely influencing these damaging fire trends. As average global temperatures rise, researchers project that the risk of wildfires in America’s West will accelerate.

Interactive Wildfire Tracker

Comments

By Rich Fairbanks (Jacksonville Oregon 97530)
on September 27th, 2012

I worked on some of the fires that went into this analysis. In total I worked 32 years for the Forest Service. During my tenure as a fire management worker the agency went from a policy that relied heavily on direct attack to a policy known informally as “back off and backfire” after the South Canyon tragedy.  I cannot judge whether this change is the right thing to do, but I can suggest that it may influence final fire size.  I would humbly suggest that you be careful in relying on Forest Service statistics.

Reply to this comment

By Bryan Bird (Santa Fe, NM)
on January 16th, 2013

http://www.nasa.gov/topics/earth/features/beetles-fire.html

Beetle damaged forests are actually less susceptible to wildlife.

Reply to this comment

By RealOldOne2
on March 23rd, 2013

The whole premise of this article is flawed. If wildfires were driven by climate (increased temperature), the number of wildfires would increase. The empirical data says they have decreased, not increased. The change in acres burned is due to forest management practices, not increasing temperatures.

Over the last 50 years, the number of wildfires in the U.S. has been dropping by ~1500 fires per year. Source: http://www.nifc.gov/fireInfo/fireInfo_stats_totalFires.html

While the acres burned per fire is increasing, this is a result of misguided forest management practices, not increased temperatures and global warming.
“Modern management practices designed to protect forests (for example, restricting thinning or excessive harvesting) have produced increasingly dense vegetation. In recent years, wildfires occurring in overstocked forests consumed brush and smaller trees (ladder fuels), growing into larger, more intense fires involving hundreds to thousands of acres.” Source: http://www.energy.ca.gov/2009publications/CEC-500-2009-080/CEC-500-2009-080.PDF

This wildfire story is just a global warming alarmist meme.

Reply to this comment

By AlexR
on May 3rd, 2013

Obviously there can be more than one influence on the number of acres burned, but it makes sense that increasingly wide swings between wet and drought will at least affect regional wildfire ‘intensity’. I don’t see why the ‘number’ of wildfires should necessarily have already increased over the past 50 years, when suppression activities (and more sophisticated detection) are still often the rule. And I’d think overall the number of fires is more related to ignition events, while the background conditions (including forest health, climate, and interactions therein) affect fire size and intensity.

Reply to this comment

By Billovitch (UK)
on July 4th, 2013

@Realoldones,

Before dismissing the arguments as “alarmist meme” (sic) you would do well to check the pedigree of the NIFC figures you quote. It turns out that NIFC don’t believe there has been the fall in fires that you are claiming. If you scroll down to the end of the URL you quote you will see the following:

“The National Interagency Coordination Center at NIFC compiles annual wildland fire statistics for federal and state agencies. This information is provided through Situation Reports, which have been in use for several decades. Prior to 1983, sources of these figures are not known, or cannot be confirmed, and were not derived from the current situation reporting process. As a result the figures above prior to 1983 shouldn’t be compared to later data”.

....and it is at 1983 that there is a sudden fall in the number of fires per year.

So, your claims are untenable. A quick search of anti-AGW sites indicates that the meme that YOU, realoldones, are propagating based on this dataset is certainly a popular one.

Reply to this comment

By billovitch (UK)
on July 4th, 2013

@realoldone2

Another point: the quotation that you give in your post is not to be found in the California Energy Office paper that you claim as its source. I suggest you check your references before dismissing the arguments to which you clearly take exception.

Reply to this comment

By Christopher Smith (97301)
on November 20th, 2013

Would it be possible to post the detailed statistical results associated with the figures in this report? I see that the best fit lines associated with each of the regressions look persuasive, but I can’t tell whether these associations are actually statistically significant without more information (say, for example, p-values, test statistics, r-squared values)

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