By Anthony LeRoy Westerling
23 May 2016
(The Conversation) – Dramatic images of out-of-control wildfires in western North American forests have appeared on our television and computer screens with increasing regularity in recent decades, while costs of fire suppression have soared. In 2015, federal spending on suppression exceeded US$2 billion, just 15 years after first exceeding $1 billion. Something has been changing our fire seasons.
There are competing explanations for why wildfires have been increasing, particularly in our forests. I’ve been studying the science of climate and wildfires for more than 15 years and the take-home message from our research is that, while our management of the landscape can influence wildfire in many different ways, it is a warming climate that is drying out western U.S. forests and leading to more, larger wildfires and a longer wildfire season.
A look at the latest data
Ten years ago, several colleagues and I set out to see if we could quantify the changes in wildfire, particularly in mountain forests of the western U.S. We wanted to see if climate might be causing some of the increase in wildfire.
In our paper, we concluded that wildfire had indeed increased substantially in western U.S. forests beginning in the 1980s. We also found that most of this increase was from fires burning primarily in mid-elevation northern U.S. Rocky Mountain forests in years with an early snowmelt.
Our latest research shows that wildfire activity in western U.S. forests has continued to increase, decade by decade, since the 1980s.
We looked at federally managed forests in the Sierra Nevada, Southwest, Pacific Northwest, and northern and southern Rockies. Over the decade through 2012, large fires (fires greater than 1,000 acres or 400 hectares) were 556 percent more frequent than in the 1970s and early 1980s. And the area affected increased even more dramatically: the forest area burned in large fires between 2003 and 2012 was more than 1,200 percent greater than in the period between 1973 and 1982.