“The forested places that burned were intellectually really interesting in terms of the patchiness,” Fleishman says. “But then, you look down and see strange, light-colored squares and realize, ‘oh my gosh, those are concrete pads where homes used to be,’ and that was terribly sobering.”
< Erica Fleishman
Before European settlement, most forest fires were ignited by lightning strikes. “There is very little evidence that [indigenous people] had any effect on the fire regimes of the forest,” says Julia Jones, Distinguished Professor of geography in the College of Earth, Ocean, and Atmospheric Sciences at Oregon State. “Although the Native peoples did migrate seasonally from the [Willamette] Valley up into the mountains, they occupied specific parts of the landscape, particularly wide, low-elevation valleys, and flat broad ridges, such as the upper ridges of the H.J. Andrews Experimental Forest.” In other words, they had no need to set fire to dense forests — that’s not where they spent their time.
Julia Jones >
European settlers, traveling west, brought new ignition sources with them, in the form of campfires. “In the 1850s or so, Europeans began to arrive across the Cascades on the Santiam Wagon Trail, and some of their campfires escaped and blew westward into the forest,” Jones says. “So, we had a new ignition source in forested landscapes.”
For one thing, Oregon experienced what is called a “flash drought” in August and September. O’Neill says: “Around middle to late August and early September, we had one of the warmest periods on record in a lot of Oregon, creating a flash drought. This is basically where you have a heat wave that can last a couple of weeks, and it rapidly evaporates off any remaining moisture. In this case, climate change exacerbated typical summertime drying, and was a contributing factor in creating the flash drought.”
< Larry O'Neill
Those winds can be partially explained by a meteorological pattern called an Omega block. As the name suggests, the pattern resembles the Greek letter Omega, with the round part representing a high-pressure ridge that hung off our coast, and the “feet” representing a low-pressure system. This blocking pattern contributed to strong, dry, easterly winds that stretched from the Canadian border into northern California. The easterly winds whipped up fires already underway and ignited new ones by toppling power lines.
By themselves, the winds were indeed unusual, but scientists are starting to look at the interacting effects of two or more variables — called a compound extreme. Independently, the easterly winds and dryness were highly unusual but not unprecedented. Yet the extent to which these two things coincided had never before been recorded. It was the perfect punch.
“Since spring was historically dry, 2021 has the potential to be another tough and long fire season in much of Oregon, particularly in central and southern Oregon,” O’Neill says. “Compounding this situation in these regions is that they’re into the second consecutive year of severe-to-extreme drought.” In recognition of these conditions, as of July parts of Oregon were placed in an above-normal fire category by the National Interagency Fire Center.
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