The Evolution of Washington’s Wildfire Regime: How climate change, fuel loads, and varied ecosystems contribute to landscape-level changes

Wildfires are so common in eastern Washington that “fire season” has become entrenched in local vocabularies.  The dry side of the state has been the site of repeated megafires in the last decade—fires that have taken lives, destroyed property, and charred hundreds of thousands of acres of forest and shrub-steppe. 

Climate change is one reason that the state’s wildfires have become larger and more frequent, but it is not acting in isolation, said Maureen Kennedy, a fire ecologist at the University of Washington Tacoma, in a recent interview.  Fire regimes are also responding to changes in fuel availability and to the state’s varied ecosystems. 

On its own, said Kennedy, “climate change is increasing the length of the fire season,” creating “more opportunities for fires to actually start and erupt.”  Dead wood and plant litter accumulated during more than a century of fire suppression have created a continuous fuel supply that didn’t exist 100 years ago.  Coupled with the hotter and drier conditions caused by climate change, that fuel build-up “is creating conditions for more intense wildfire,” Kennedy said. 

Native ecosystems also play a role in fire susceptibility.  “The effect of climate change … is really going to depend on what the climate is to begin with,” Kennedy said.  She and her colleagues have found that landscapes where summers are already hot and dry don’t respond as strongly to climate change as cooler, wetter ecosystems where higher temperatures are drying out fuels that might otherwise be too wet to burn. 

Based on predictive models, Kennedy anticipates that, in addition to affecting susceptibility to fire, climate change will alter the ways in which forests grow after they have burned.  High-elevation forests, where short summers limit plant growth, may become more productive.  Hotter, drier landscapes could regenerate more slowly as they face moisture stress induced by higher temperatures and lower precipitation.  At the same time, models suggest that rising temperatures will speed decomposition of dead plant materials.  With less fuel available, those landscapes, now Washington’s most fire-prone, may eventually become less likely to burn. 

As climate change has lengthened Washington’s fire season, it’s also shortened the period during which prescribed fire and other fuel mitigation treatments can be conducted.  Understanding how climate change affects wildfire can inform decisions about land use, fuel-reduction treatments, and fire preparedness, and help land managers make the best use of that reduced window of opportunity.  Fire season is likely to be a fixture in Washington for decades to come.  While we may never be at ease with wildfires and the accompanying smoke, science can help us learn to live with them.