The fire season will soon be here and we all hope it won’t be as devastating as the last few fire seasons were, when fires swept through large swathes of forests and national parks and destroyed entire neighborhoods in the Western US. Now the increase in the number of fires has been linked with global warming, since it brings us an earlier?and drier?spring.
A new study led by scientists at Scripps Institution of Oceanography at the University of California, San Diego, implicates rising seasonal temperatures and the earlier arrival of spring conditions in connection with a dramatic increase of large wildfires in the western United States.
In the most systematic analysis to date of recent changes in forest fire activity, Anthony Westerling, Hugo Hidalgo and Dan Cayan of Scripps Oceanography, along with Tom Swetnam of the University of Arizona, compiled a database of recent large western wildfires since 1970 and compared it with climate and land-surface data from the region. The results show that large wildfire activity increased “suddenly and dramatically” in the 1980s with longer wildfire seasons and an increased number and more potent wildfires. The new findings point to climate change as the primary driver of recent increases in large forest fires.
“The increase in large wildfires appears to be another part of a chain of reactions to climate warming,” says Cayan. “The recent ramp-up is likely, in part, caused by natural fluctuations, but evidence is mounting that [climate change has] been contributing to warmer winters and springs in recent decades.”
Western U.S. wildfires have consumed hundreds of homes and huge areas of forest and national park land in the last 34 years. Fire-fighting expenditures for wildfires now regularly exceed one billion dollars per year.
The scientists compiled a comprehensive time series of 1,166 forest wildfires of at least 1,000 acres that had occurred between 1970 and 2003 from wildfire data covering western U.S. Forest Service and National Park Service lands. To investigate what role global warming might play, they compared the timing of snowmelt and spring and summer temperatures for the same 34 years. The results point to a marked increase in large wildfires in western U.S. forests beginning around 1987, when the region shifted from predominantly infrequent large wildfires of short duration (average of one week) to more frequent and longer-burning wildfires (five weeks).
The researchers established a strong association between early arrivals of the spring snowmelt in the mountainous regions and the incidence of large forest fires. An earlier snowmelt can lead to an earlier and longer dry season, which provides greater opportunities for large fires.
Thomas Swetnam, director of the Laboratory of Tree-Ring Research at The University of Arizona, says, “I see this as one of the first big indicators of climate change impacts in the continental United States. We?re showing warming and earlier springs tying in with large forest fire frequencies. Lots of people think climate change and the ecological responses are 50 to 100 years away. But it?s not 50 to 100 years away?it?s happening now in forest ecosystems through fire.”
Art credit: gimp-savvy.com
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