Author(s): Jesse Roman. Published on November 1, 2016.

Dry & drier

A new study quantifies the impact of human-generated climate change on the threat of wildfire in the western U.S.


FOREST MANAGERS HAVE NOTICED a disturbing trend that statistics unfortunately corroborate: the wildfire problem across the United States, especially in the Western states, is growing worse.

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It is well understood that extended droughts and increasing temperatures over the past several decades have measurably increased the “fuel aridity” of the landscape—essentially, the dryness of the forest and climate—but to what extent and how humans have contributed to the problem have been lesser known. A study published in October in the Proceedings of the National Academy of Sciences suggests the human impact has been profound.

In the study, “Impact of Anthropogenic Climate Change on Wildfire Across Western U.S. Forests,” researchers from the University of Idaho and Columbia University estimate that human-caused climate change contributed to nearly 10.4 million acres, or more than 16,000 square miles, of additional forest fire area during the period 1984–2015, nearly doubling the forest fire area expected in the absence of human-related climate change, according to the study.

While both normal climate variations and human-caused climate change are working in tandem to dry out the landscape, computer climate models used in the study estimate that human-caused activity has “significantly enhanced fuel aridity.” Researchers used eight metrics to measure the dryness of the climate and wildlands themselves, factors that correlate with wildfire risk. Overall, from 2000 to 2015, climate change has caused 75 percent more forested area to have high fire-season fuel aridity and has led to an average of nine additional days per year of high fire potential, the researchers found.

Wildfire statistics seem to bear out the increased fire risks described in the study. In 2015, a record 10 million acres burned across the nation, and for the first time in its history the U.S. Forest Service spent more than half of its annual budget on suppressing wildfires. All told, more than $1.7 billion was spent suppressing wildfires, according to the Forest Service.

The wildfire problem has also been exacerbated by increased human settlement and suppression activities, which have led to higher fuel loads across the landscape, the study noted. With the heating climate serving to make that fuel load ever more tinderlike, wildland blazes would be expected to grow larger faster and burn with more ferocity than they did decades ago. That’s exactly what is happening.

“People tell me that they’ve never seen fires as active as what they’re battling right now,” Dr. A. Park Williams, one of the study’s authors and an assistant research professor at Columbia’s Lamont-Doherty Earth Observatory, told The New York Times in October. “What we’re seeing in fire world [today] is much different than what we saw in the 1980s, and in the 2030s, fires will be unrecognizable to what we’re seeing now.”

JESSE ROMAN is associate editor for NFPA Journal.