SACRAMENTO, Calif. — A new report by an international research team examined the historical pattern between weather and wildfires in California.
Increasing temperature due to climate change, heavy fuels in forests, and fire suppression policies are key reasons for the recent worsening of fire conditions over the past century, the study found.
Valerie Trouet is one of the lead investigators on the project that was recently published in the Proceedings of the National Academy of Science of the United States of America. She is a tree-ring scientist and an associate professor at the University of Arizona.
“I spent months traveling in a rental car up and down the Sierra Nevada looking for stumps that had fire scars in them,” Trouet said.
The team recorded information from the rings of thousands of fire-scarred trees in order to date and find the historical severity of wildfires in California dating back to 1600. Researchers cited historical data on temperatures, precipitation and fires in their research.
The team then cross-referenced that information with historical data on the North Pacific Jetstream (NPJ), a high altitude wind pattern that occurs over the Pacific Ocean. The study found a pattern between wildfire and weather activity caused by the (NPJ) between 1600 and 1904.
Winters that brought heavy rain were typically followed by low-activity wildfire seasons, the study found. Dryer than normal winters were typically followed by high-activity wildfire seasons.
“What we found that in recent decades… at about 1980, that connection is gone,” Trouet said.
Researchers say rising temperatures coupled with fire suppression policies have led to worsening conditions seen over the past century.
U.S. fire suppression policies have led to an increased fuel load in forests, Trouet said. Pre-1900 historical data shows that small fires would burn across California every five to 10 years.
“You know we’ve been putting out all of these fires for about a century now,” Trouet said. “So, instead of frequent ground fires, you now get a century of fuel buildup. And now when a fire burns, there is so much fuel that you no longer have these mild ground fires here. You get destructive ground fires that are much harder to control.”
On a global scale, Trouet says people must mitigate rising temperatures as a result of climate change. On a local scale, the state should consider clearing underbrush in forests and prescribed burns to mitigate dangerous wildfires in California.
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