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Burn severity — not just size — from megafires matters.

BY YOOHYUN JUNG | JULY 25, 2022 | UPDATED: JULY 25, 2022 1:28 PM

https://www.sfchronicle.com/projects/2022/california-wildfire-severity-map/


"Many of the largest wildfires in recent U.S. history have happened in California just in the past few years, including last year's Dixie Fire, which burned nearly a million acres across four counties. Seven others in 2021 achieved "megafire" status, surpassing the mark of 100,000 acres burned. No megafires have occured in 2022 yet, but the ongoing Oak Fire, which started on July 22, has already burned more than 15,000 acres and continues to grow.


But size, it turns out, isn't all that matters, according to fire experts. By itself, it's a poor indicator of fire’s actual impact.


"Forests in California have been burning forever," said Scott Stephens, co-director of Berkeley Forests at UC Berkeley and wildland fire science professor.


In a more distant past — pre-1800s, before colonial settlement in California, fire of the highest severity made up only an estimated 1% to 5% of total acreage burned, Stephens said. Recent fires such as Dixie exceeded 40%, which is "off the scale, so much you can't even imagine," he added.


The severity indicates forests' ability — or a lack thereof — to bounce back from fires and withstand prolonged drought conditions, as well as the cascading impacts of climate change.


The Chronicle analyzed the burn severity of some of the most significant wildfires in California in 2021. The burn indices show just how deeply fires such as Dixie and Caldor have scarred their environments in the places they burned most severely, while leaving other portions unscathed. Some blazes, such as the Monument Fire, grew massive without burning as severely, which researchers say can be beneficial to the environment.


Megafires with high burn severity are a reflection of a landscape changed over centuries by exploding populations and suppression-oriented fire management policies and practices — one in which flame-friendly shrubs grow where trees once stood, making the environment even more vulnerable to fires.


"A lot of these forests are not going to be forests again," Stephens said. "I hate to say it, but it's true. I think that our grandkids are going to inherit a forest ecosystem that none of us will recognize."

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