In a Warmer Northwest, There Are More Large Fires

Even under low-emissions greenhouse gas scenarios, the probability of very large wildfires increases by at least 30 percent by 2100 in the West, according to a new study published in Climatic Change and led by Natasha Stavros of NASA’s Jet Propulsion Laboratory. The Rocky Mountain region showed the largest increase in probability, followed by the Pacific Northwest.

The Stavros study, coauthored by CIRC researcher John Abatzoglou, lends important new data to several previous studies linking climate change and variability to wildfire extent in the western United States. Stavros and colleagues used a detailed statistical approach to link very large wildfires (more than 50,000 acres) to weekly variability in weather and weather-derived variables such as temperature, fuel moisture and energy release across eight regions in the western U.S. defined by fire-management agencies.

In most regions there’s a noticeable difference between low-emissions greenhouse-gas scenarios (RCP 4.5) and high-emissions scenarios (RCP 8.5) in the probability of large fire occurrence linked to weather conditions on weekly timescales. The study also looks at how those conditions will change in the future. Unlike studies using only fire-danger indices or changes in annual area burned, the current study derives relationships between climate and the likelihood of large fires directly.

Their approach worked well to simulate past fire occurrence. The authors compared observed past fire occurrence in each of the eight regions with simulated fire occurrence using weather output for the past from climate models. For seven of the eight regions (the western Great Basin being the exception), the modeled and observed probabilities were statistically indistinguishable.

Citation: Stavros, E.N., J.T. Abatzoglou, D. McKenzie, and N.K. Larkin (2014) Regional projections of the likelihood of very large wildland fires under a changing climate in the contiguous Western United States, Climatic Change 126:455–468. doi:10.1007/s10584-014-1229-6
Photo Caption: Lightning strikes the Warm Springs Indian reservation in 1999, photographed by a wildland fire engine crew member.

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