A study describes the effect of summer precipitation on wildfire activity in the western United States. Increases in wildfire activity in the western United States in recent decades have been attributed to increased temperatures and decreased winter snowpack. However, how changes in precipitation drive wildfire activity remains unclear. Zachary Holden and colleagues used satellite-derived maps of forest wildfire areas and quantified summer precipitation changes during the May-September fire season to study the influence of precipitation on wildfire activity in the western United States from 1979 to 2016. The analysis also included data on humidity, snow water, and temperature. The study revealed that summer precipitation and wetting rain days (WRD)--defined as days with precipitation greater than or equal to 2.54 mm--exhibited declines across 31-35% and 36-45% of the study areas, respectively. After accounting for the relative influence of precipitation, snowpack, and temperature on wildfire activity, the authors found that WRD anomalies had a significant effect on wildfire activity, suggesting that precipitation, through wetting and air moisture effects, might act as a primary driver of wildfire activity in the western United States. According to the authors, continued decreases in summer precipitation in combination with increases in summertime aridity might result in elevated future wildfire activity in the western United States.
Article #18-02316: "Decreasing fire season precipitation increased recent western US forest wildfire activity," by Zachary Holden et al.
MEDIA CONTACT: Zachary Holden, United States Forest Service, Missoula, MT; tel: 406-396-3151; e-mail: zaholden@fs.fed.us
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Proceedings of the National Academy of Sciences