“It took a rather anomalous event to cause those conditions to come together last year,” said Ranil Dhammapala, an atmospheric scientist with the Washington Department of Ecology. “It’s not to say those won’t ever happen again, but those rare events have to kind of gang up on you for that kind of episode to happen again.”
However, smoke events are definitely becoming more common, he added, and have reached a new level of intensity in the past decade. And as a general rule, more seasonal wildfires produce more smoke, leading to more chances for it to find its way into Clark County.
Air quality changes
The local impact of wildfire smoke can be seen in local air-quality metrics.
“We rarely, if ever, had problems with unhealthy air from wildfire smoke in Southwest Washington prior to 2015,” said Uri Papish, executive director at the Southwest Washington Clean Air Agency.
Data from the Department of Ecology’s two Clark County air-monitoring stations — one in Vancouver and one in Yacolt — shows a trend toward more days per year with poor air quality overall, and a trend toward worse quality on the bad days. From 2006 to 2014, local air quality was always rated “Good,” “Moderate” or, at worst, “Unhealthy for sensitive groups.”
“Unhealthy” days appeared for the first time in 2015 and occurred again in 2017, 2018 and 2020. “Very unhealthy” and “Hazardous” days occurred for the first time in 2020. The years 2017 and 2020 were also the only ones in which the overall percentage of “Good” days per year fell below 90 percent at either of the two monitoring stations.
“We used to have our worst air-quality days in the winter months,” Papish said. “That’s when we had inversion layers. And we had air pollution caused by wood stoves and fireplaces — wood-burning — occurring during the winter months.”
That pollution pattern is shifting toward the summer. The Clean Air Agency has measured the levels of PM 2.5 — the dangerous particles from smoke — in Vancouver’s air since 2007. From 2007 through 2014, the highest 24-hour count of the year always occurred in November, December or January. From 2015 onward, it’s been a roughly 50-50 split, with half of the worst days occurring in August or September.
Smoky air is inevitable if a wildfire occurs close to home, Dhammapala said, but the smoke that blanketed Western Washington and Oregon last summer came from farther away. Weather systems can transport smoke to the Portland area from wildfires as far off as British Columbia and California.
The probability of Vancouver being impacted by far-away fires is heavily dependent on the weather. There’s no single weather pattern that makes it happen, he said, but generally sustained high pressure produces east winds that can move smoke from Eastern Oregon and Washington to the western areas — although it takes additional factors to make it stay there.
“You’ve got to have meteorology that doesn’t work in your favor, as in doesn’t dissipate the smoke,” Dhammapala said.
That’s what happened last year. Strong east winds drove smoke from California and Oregon wildfires westward until it hit an area of lower pressure just offshore, where the smoke began to pool into an enormous plume.
Cooler temperatures then brought the plume back onto land above Western Washington and Oregon, but the pressure systems at the time didn’t allow for much more wind, Dhammapala said, so the smoke sat in place for days on end.
The weather pattern itself could have happened without the smoke, he added, but it wouldn’t have been a hazard — it was only because it happened to coincide with the wildfires that it resulted in the creation of a giant pocket of polluted air.
“The bottom line is more fires equals more smoke,” Dhammapala said. “But will that just sit over us for days? Will that smother the entire state? Will that be confined to areas immediately downwind of the fires? Those are the variables that are produced by the meteorology of the day.”
Forests closest to the coast are predominantly spruce and hemlock, transitioning to Douglas fir farther inland. Major wildfires are historically rare among those types of trees, he said, occurring only about every 400 years on average. One example is the 1902 Yacolt Burn, which covered about 500,000 acres across parts of Southwest Washington.
Ponderosa pine forests east of the Cascades see far more frequent fires, Bailey said — more like a couple times per decade — although historically those tended to be lower-intensity surface fires. However, recent eastern fires have grown more intense due to hot, dry conditions.
The probability of smoke traveling to the Portland metro area is weather-dependent, but it is also influenced by the frequency of the fires, and that’s where climate change comes into play.
Climate scientists predict that the warming climate will produce hotter summers and smaller snowpacks in the Cascades and Rockies, Wineke said, which will result in larger and more frequent western wildfires.
Climate change is correlated with an increase in wildfires because it exacerbates some of the factors that determine the probability of whether a wildfire will erupt, Bailey added. Most prominently, warmer weather leads to longer fire seasons with drier fuel that becomes more readily able to burn.
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That’s by no means the only causal factor, he added — residents are also distributed over a wider geographic area, putting more structures in danger and creating more opportunities for people or equipment to accidentally spark wildfires.
Land- and forest-management policy choices also play a role by allowing fuel to accumulate and connect, creating pathways for fire to spread. The Bootleg Fire currently burning in Southern Oregon is an example of that problem, Bailey said.
“But certainly the easy one is just the length of the fire season, which includes how dry the fuels are,” he said. “That has already been happening and is clearly projected to continue longer and longer.”