Western U.S. wildfire smoke plumes are getting taller, researchers find

The Western wildfire smoke plumes have gotten higher in recent years, with more smoke and aerosols lofted up where they may travel further and have an influence on air quality over a larger area. Climate change is most likely to blame, since the Western United States has more aridity and less precipitation, which exacerbates wildfire activity.

According to Kai Wilmot, a postdoctoral researcher in the Department of Atmospheric Sciences at the University of Utah, "should these trends persist into the future," increased Western U.S. wildfire activity will probably coincide with more frequent air quality degradation on a local to continental scale.

The iNterdisciplinary EXchange for Utah Science, or NEXUS, at the University of Utah provided funding for the study, which was published in Scientific Reports.

Smoke volume

Wilmot and U colleagues Derek Mallia, Gannet Haller, and John Lin modelled plume activity for about 4.6 million smoke plumes in the Western U.S. and Canada between 2003 and 2020 to examine trends in smoke plume height. The researchers divided the smoke plume data into EPA ecoregions (regions with comparable ecosystems, such as the Great Basin, Colorado Plateau, and Wasatch and Uinta Mountains in Utah), and then they looked for trends in the maximum smoke plume height measured during August and September in each region each year.

The research team discovered that the highest plume height grew by an average of 750 feet (230 meters) every year in the Sierra Nevada ecoregion of California. Maximum plume heights rose by an average of 320 feet (100 meters) each year in four locations.

Why? According to Wilmot, the combination of atmospheric factors, fire size, and heat emitted by the fire results in complicated plume heights.

"We're witnessing larger and more severe wildfires throughout the Western U.S.," he adds, "given trends pushed by climate toward rising air aridity, decreased snowpack, higher temperatures, etc." Because of this, there are now more severe flames and greater burn zones.

In order to calculate the mass of the plumes and assess the trends in the quantity of particles being thrown into the atmosphere by wildfires, which is also growing, the researchers used a smoke plume simulation model.

The pyrocumulonimbus cloud phenomena, in which smoke plumes begin to produce thunderstorms and their own weather systems, was also calculated using the smoke simulation model. Six ecoregions saw their first pyrocumulonimbus clouds between 2017 and 2020, and the pattern indicates that this activity is occurring on the Colorado Plateau more frequently.

According to John Lin, a professor of atmospheric sciences, taller plumes carry more smoke to higher elevations where it might spread further.

"Smoke has the potential to be carried over longer distances when it is lofted to higher elevations, reducing air quality across a greater territory," he claims. Therefore, the problem of wildfire smoke can expand from a localized problem to a regional or even global one.

Are the trends picking up speed?

Recent years have seen some of the most severe fire seasons. Does that imply that the rate at which the fire trend is worsening is accelerating? Wilmot claims that it is too soon to say. It will need many years of data to determine whether a substantial change has occurred.

He notes that the years 2017 to 2020 contain many of the most severe data points, with certain 2020 values literally towering above the rest of the timeseries. Furthermore, it seems likely that a study of data from 2021 would further corroborate this result given what is known about the 2021 fire season.

Though plume height and aerosol concentration trends are growing in Utah's Wasatch and Uinta Mountains ecoregion, they are not as pronounced as those in Colorado or California. However, smoke from nearby states frequently overflows into the alpine basins of Utah.

It doesn't seem like Utah is the heart of this problem, according to the plume trends themselves, adds Wilmot. The risk to Utah's air quality from wildfire activity in the West, according to trends in plume top heights and wildfire emissions in California, however, is rising given that we are normally downwind of that state.

Although there are some things that individuals can do to assist, such as minimize human-caused wildfires, Wilmot asserts that climate change is a far bigger and stronger factor that is causing trends of less precipitation, more aridity, and riper fire conditions throughout the West.

Even if we immediately reduce emissions, Wilmot continues, "some of these [climate change] implications are already baked in." "Right now, it feels like we are mostly just along for the trip."

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Materials provided by University of Utah. Original written by Paul Gabrielsen. Note: Content may be edited for style and length.