When one reads about the possibility of wildfires in the Northwest and California, the media and others tend to focus on temperature and humidity.
Certainly, warm temperatures, lack of rainfall and dry fuel contribute to wildfires (although excessive rainfall in the previous period can lead to more fuel and wildfires).
But there is another key parameter for starting and growing wildfires: strong winds. And in the western United States, strong easterly winds (from the east) descending on regional topography are of particular importance.
Wind plays a central role in wildfires in the Northwest, with nearly all major events associated with strong winds or rapid wind deflections.
Wind is important for a number of reasons. Strong winds provide plenty of oxygen for the fire. It pushes embers, firewood, and superheated gases toward the front of the flame, facilitating rapid spread. Wind helps dry fuel on surfaces, such as grass and vegetation. High winds can cause fires, such as when winds damage electrical infrastructure causing sparks and flames (e.g. tree branches falling on power lines). Rapid wind changes can kill firefighters, especially if they are in canyons or valleys.
Wind is just as important as other well-known factors that regulate wildfires, such as temperature and precipitation. It turns out that virtually all major wildfires west of the Cascade Peak are associated with strong easterly winds. The largest wildfires east of Washington are associated with strong winds.
Consider the deadliest fires in the Pacific Northwest since 1900 (see table below). The 1902 Yacoult Burn was the biggest killer (65+) and was associated with extreme easterly winds. The famous Great Fire of 1910 killed 38 people and was accompanied by strong winds combined with a cold front (which Tim Egan in his book called Wind Palouse).
The Beachie Creek Fire in 2020 killed five people as strong easterly winds accelerated down the western slopes of the Cascades. The Thirty Mile Fire killed four firefighters when the wind changed direction quickly, while they were on the front line fighting the fire. Similar to Twinp River Fire.
I could continue, but you get the message. Almost all deadly fires in Washington State involve very strong winds or very strong/fast wind deflections.
What about the biggest fires in the Northwest (see below)?
It’s all related to strong winds. The major fires in western Washington and Oregon were both associated with strong easterly winds. The major fires east of the Cascades are accompanied by strong winds but can be slightly weaker as the flames cover lawns or pastures.
Dry, hot conditions and the absence of strong winds rarely cause large wildfires in the region and often cause few deaths.
And for those concerned about wildfire smoke, wind also plays an important role in our region. Consider last fall’s Bolt fire. The fire was started and spread by unusually strong easterly winds, which blew smoke into western Washington.
Key message: don’t underestimate the important role of wind in starting and spreading wildfires in the Northwest.
So, if wind is so important for wildfires, how has climate change changed northwesterly winds? And how will the critical easterly winds change as the planet warms?
My team and others are working on this, and one of my graduate students is examining wind trends. At this point, it seems likely that the historical trend of winds has been relatively small over the past 50 years, and strong easterly winds will weaken (and thus be less likely to support western wildfires) as the earth warms. (see chart from a climate simulation region below for a location near the top of the central Washington Cascades).
Therefore, a major contributor to Northwest forest fires can be reduced by global warming, another example of the nuances associated with wildfires.
