Science Source

Decreasing fire season precipitation increased recent western US forest wildfire activity

States that increases in area burned by wildfires in the western United States have been widely attributed to reduced winter snowpack or increased summer temperatures
Shows that previously unnoted declines in summer precipitation from 1979 to 2016 across 31–45% of the forested areas in the western United States are strongly associated with burned area variations
Shows that the number of wetting rain days (WRD; days with precipitation ≥2.54 mm) during the fire season partially regulated the temperature and subsequent vapor pressure deficit (VPD) previously implicated as a primary driver of annual wildfire area burned
Uses path analysis to decompose the relative influence of declining snowpack, rising temperatures, and declining precipitation on observed fire activity increases
Results suggest that precipitation during the fire season exerts the strongest control on burned area either directly through its wetting effects or indirectly through feedbacks to VPD