Last updated October 10, 2018

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