Warming and earlier spring increase western U.S. forest wildfire activity
The authors compared the annual frequency of large wildfires (> 400ha) to hydroclimatic and land surface variables, specifically mean temperature (March-August), timing of spring snowmelt, and fire season length to determine if the fire frequency of large fires has changed and if that change is due to climate factors.
The authors found that large fire occurrence has been increasing in response to earlier snowmelt and increasingly warmer temperatures in the early spring months in many areas of the West since the early 1980's. Fire season length has increased by 78 days since 1970, and annual area burned has also significantly increased by at least six and a half times over the same time period. These increases and the interannual variability were strongly correlated with average summer temperatures and the timing of spring snowmelt.
The authors suggest that the earlier Spring snowmelt and higher early season temperatures may lead to longer and drier dry seasons, providing increased opportunities for fire ignition and spread, and as temperatures continue to warm, wildfires will become larger and more frequent.