Washington: Warming and Wildfires

• Published: September 2nd, 2009

Program Summary

In recent years, the state of Washington, like other Western states, has seen a significant increase in wildfires. So far, almost twice as much land has burned this decade than during the 1970’s, 1980’s and 1990’s combined. Almost all of this activity has been on the drier east side of the Cascade Mountains.

Why is it happening? For a number of reasons, but at least one, say scientists, is climate change. Since the 1950’s, temperatures in the state have been rising; spring temperatures, in particular, have gone up nearly three degrees on average. Natural variability still makes some years warmer, some cooler, but the overall trend has been upward. And in years with unusually warm temperatures, more acreage tends to go up in smoke.

This warming trend leads to more fire damage in several ways. First, warmer springtime and summer temperatures make leftover winter snows melt sooner. That makes forests dry out earlier in the summer than they once did, and lengthens the overall potential fire season. Beyond that, warmer summers put more stress on vegetation, leading to an increase in mortality. Dead vegetation can be easier to ignite than living plants.

Warmer temperatures also lead to another source of disturbance in the forests of Washington and much of the West. Spruce beetles and mountain pine beetles are voracious pests that thrive in warmer weather, and which find it easiest to attack trees that are already under stress. By eating their way into the vital tissues of spruces and pines, the beetles kill trees by the thousands, creating dead, dry fuel that can easily be ignited by lightning strikes or careless humans.

Massive beetle infestations during the past 10 years may in fact have set the stage for the so-called Tripod Complex fire that swept through the Okanogan-Wenatchee forest in 2006, burning some 180,000 acres of woodland, destroying wildlife habitat and costing the state tens of millions of dollars. It can take a full century for the scar of a wildfire like the Tripod — or even a smaller blaze like the Oden Road Fire, which burned 10,000 acres in the same forest in late August of this year — to disappear completely.

In the short run, say local residents, there’s also the problem of property damage and lost revenue, as the fires and their aftermath keep wilderness enthusiasts away. The smoke from wildfires, moreover, can irritate the eyes and air passages of people living nearby, and can trigger or worsen asthma, bronchitis and other pulmonary diseases, especially in young children and the elderly.

This is not to say that warming temperatures are the only factor in more frequent and severe fires. Another may be the fact that the U.S. Forest Service has traditionally fought fires aggressively, which allows both dead vegetation and young, living trees to build up rather than burn off. Over time, that makes it more likely that fires will happen more often and burn longer. Newer Forest Service policies try to counteract the problem by thinning trees, prescribing burning and letting some natural fires burn to consume the excess fuel. Washington authorities are also considering another strategy: clearing out woody debris, such as trees killed by beetles, and converting that biomass into fuel.

If temperatures in Washington continue to warm, however, the extent to which new forest management practices can counter the effects is unclear. Under threat from fires and beetles, the fate of forests in the Evergreen State is an open question.

Credits: National Interagency Fire Center, Noblèt Productions, WA DNR, US Forest Service, NASA, Rich Wood, Nick Mickel, Russ Armstrong