Likelihood of extreme autumn fire weather has increased 40%

Climate change has increased the likelihood of hot, dry, windy autumn weather that can set the stage for severe fires in California and western Oregon, according to new computer models.

The study led by Oregon State University's Linnia Hawkins looked at the role climate change may have played in extreme fire weather conditions that accompanied recent large September, October and November fires in those states.

David Rupp of the Oregon Climate Change Research Institute was part of a collaboration that looked at the weather conditions during big fires caused by strong offshore winds.

The winds were reduced in the two years studied by the modeling. The four study areas were more likely to have extreme autumn fire weather than they would have been without human-caused increases in atmospheric aerosols and carbon dioxide.

Over the last few years, California and western Oregon have experienced their largest and most destructive wildfires ever recorded.

The scientists focused on conditions like those seen during recent catastrophic fires, including Northern California's Wine Country fires in October 2017, the Camp Fire in November 2018, and the North Complex Glass fires in September 2020.

Climate change has increased the likelihood of extremely hot, dry and windy weather in autumn, but it has not increased the likelihood of fire.

The scientists set the atmospheric CO 2 and aerosol concentrations to mid-19th century levels to model a climate without human activity. They performed thousands of simulations with aerosol concentrations that were set to pre-industrial levels.

The researchers compared the likelihood of extreme autumn fire weather conditions to the simulations and found that they would occur once every 20 years.

When CO 2 and aerosols from human activity were included, the chance of extreme conditions was 40% higher in areas of California and Oregon where recent autumn fires have occurred. Climate change slightly decreased the frequencies of strong, dry, offshore winds.

The 40% increase in likelihood is the average across the western United States, and the increase is smaller or larger in specific regions. She stresses that the study only looked at extreme fire weather conditions and only one season of the year.

Climate change has already increased the likelihood of autumn wind-driven extreme fire weather conditions in the west, according to research. Fire risk assessments and fire adaptation efforts can be guided by approaches such as we used here.

More information: Linnia R. Hawkins et al, Anthropogenic Influence on Recent Severe Autumn Fire Weather in the West Coast of the United States, Geophysical Research Letters (2022). DOI: 10.1029/2021GL095496 Journal information: Geophysical Research Letters Citation: Likelihood of extreme autumn fire weather has increased 40% (2022, February 23) retrieved 23 February 2022 from https://phys.org/news/2022-02-likelihood-extreme-autumn-weather.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.