23 Jan 2010, 5:47pm
The 2009 Fire Season
by admin

2009 Fire Season Statistics

The 2009 Fire Season statistics have been posted at the National Interagency Fire Center, Fire Information - Wildland Fire Statistics website [here].

The total acres burned by wildfires nationally in 2009 is reported to have been 5,921,786 acres. That was more than last year, but 3 to 4 million acres less than the record years of 2005, 2006, and 2007. The average over the last ten years is 7.01 million acres.

Total Acres Burned in Wildfires, 1960-2009. Chart by W.I.S.E.

An additional 7,265 acres were reported to have burned in 33 Wildland Use fires (WFU’s). Those numbers are somewhat deceiving, because the WFU designation was mostly dropped in favor of “fires used for resource benefit” (FURB’s). The number of FURB’s and their acreage was not reported (at least not directly). For comparison, in 2007, before the FURB designation was adopted, 341 WFU’s were reported to have burned 419,685 acres, and in 2008 264 WFU’s were reported to have burned 236,834 acres.

Total number of wildfires was 78,792. That is the fewest number of wildfires since 2004 and 2005, and 62% of the average annual fire count from 1960 through 2009. The number of wildfires has been declining since the early 1980’s. That may be an artifact of the counting system. Many small fires started by multiple lightning strikes in the same vicinity are counted as one fire today, while they may have been counted as many individual fires in prior decades.

Total Number of Wildfires, 1960-2009. Chart by W.I.S.E.

In addition, delays in rapid response to small fires may result in those fires merging, and then they are counted as one fire. That can happen to large fires that merge, as well. There are many name changes and mergers of fires during the fire season, which confounds the fire count. Wildfires don’t happen in test tubes in a laboratory, and so the counting system is not as accurate and precise as some scientific studies might lead you to believe.

Another possible explanation for the decreasing number of wildfires is that human-caused and/or lightning-ignited fires are fewer today than 30 years ago. We have no data to either support or refute those hypotheses.

The average size of wildfires in 2009 was 75 acres. That is more than 2008 (66 acres per wildfire), but less than 2005, 2006, and 2007 when the average wildfire size was 131 acres, 103 acres, and 113 acres per fire, respectively.

Average fire size is not a useful statistic, though, because the distribution (number of fires by acreage class) is skewed by a few very large fires (greater than 20,000 acres). The NIFC does not report the distribution, but it is more or less in a “reverse-J” (negative exponential) shape, with many small fires, fewer medium-sized fires, and a handful of megafires out in the tail. The average fire size is also dependent on the total count of wildfires, which may be biased by inaccuracies and imprecision in the counting system, as mentioned above. We present the following chart anyway, because we have the annual data and it was easy to make the graph.

Annual Average Wildfire Size, 1960-2009. Chart by W.I.S.E.



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