The western U.S. has seen more and bigger wildfires over the last 30 years, a trend expected to continue as temperatures rise and droughts become more severe, according to a new study.
The study, accepted for publication in Geophysical Research Letters, which is published by the American Geophysical Union, examined the region from Nebraska to California from 1984 to 2011. Over that period, the number of wildfires over 1,000 acres in size increased by a rate of seven per year, the study says. Total acres burned increased by 90,000 over that time, and the largest wildfires grew by 350 acres per year.
The total area these fires burned increased at a rate of nearly 90,000 acres a year – an area the size of Las Vegas, according to the study. Individually, the largest wildfires grew at a rate of 350 acres a year, the new research says.
The study used satellite data to measure areas burned by large fires since 1984, and also looked at climate variables such as seasonal temperature and rainfall, during the same time. Most areas that saw increases in fire activity also experienced increases in drought severity during the same time period, the study says.
Max Moritz, a co-author of the study and a fire specialist at the University of California-Berkeley Cooperative Extension, says in a statement, “Twenty eight years is a pretty short period of record, and yet we are seeing statistically significant trends in different wildfire variables—it is striking.”
A statement on the study says the trends “suggest that large-scale climate changes, rather than local factors” could be driving increases in fire activity, but the study “stops short of linking the rise in number and size of fires directly to human-caused climate change. Observed changes in fire activity, though, are in line with long-term, global fire patterns that climate models have projected, the statement says.
Philip Dennison, an associate professor of geography at the University of Utah in Salt Lake City and lead author of the paper, says, “We looked at the probability that increases of this magnitude could be random, and in each case it was less than 1%.Most of these trends show strong correlations with drought-related conditions which, to a large degree, agree with what we expect from climate-change projections.”
A research ecologist not connected to the study, Jeremy Littell a research ecologist with the U.S. Geological Survey (USGS) at the Alaska Climate Science Center in Anchorage, AK, who was not connected with the study, says in the statement fire activity reported in the paper resembles what would be expected from rising temperatures caused by climate change, but he says other factors such as a response to decades of fire suppression could also be at play.
“It could be that our past fire suppression has caught up with us, and an increased area burned is a response of more continuous fuel sources,” Littell says. “It could also be a response to changes in climate, or both.”
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