What caused the devastating 2020 fire season in California?

California is the most fire-prone state in the United States. In 2020, over 9,900 wildfires burned about 4.3 million acres. A new study from the University of California, Davis has summarized the 2020 fire season and examined what drove the record-breaking fire activity.

The study said 2020 was the first year in recorded history that burned areas in California came close to rates seen before the 1800s, when an estimated 3-4 million acres burned in an average year.

Resource and fire managers have shifted their emphasis from reducing burned area to reducing fire severity and damage, and to restoring ecosystems after fire.

“The problem is that much of the burning we are seeing now is not restorative but destructive. The need to shift management goals is key, as is understanding the very important role that fuels play in driving fire severity,” said study lead author Hugh Safford. 

For the past century, the key measure of success among forest managers has been decreased burned area, but that needs to change as increased fire severity is a greater concern. 

Over the past 40 years, the increases in burned area occurred almost entirely in central and northern California forests, despite extreme warming taking place in Southern California. This is because of decades old fire exclusion policies that led to a huge increase in forest density and fuels, driving an explosion in large, destructive fires.

“In these ecosystems, reducing burned area is a cause of the current catastrophic trends, not a solution to them,” the authors said.

The researchers found that the 2020 fire season followed an accelerating, decades-long trend of increased burn area, severity, size and costs to society and the economy.

• In 2020, fires killed 33 people with overall economic losses of more than $19 billion and firefighting costs of $2.1 billion. 
• The years 2020 and 2021 together burned more area than the previous seven years combined.
• Between 2015 and 2020, total insured economic losses were more than $50 billion, and over 50,000 structures — mostly homes — were destroyed.
• The increase in forest fires resulted in more than half of Californians experiencing unhealthy, and sometimes hazardous, air quality index levels for a month or more. 
• The state’s worst five days of air pollution in history all occurred in 2020, according to CalFire.
• Wildfire-driven air quality in August and September likely also caused 1,200 to 3,000 “excess” deaths among people age 65 or older.
• Overall, the 2020 fires emitted nearly 112 million metric tons of carbon and 1.2 million tons of fine particulate matter (PM 2.5), 120 times more than California’s vehicles produced in the same year.

The study also assessed the severity patterns of the 2020 fire season. Fire severity is a measure of the impact of burning on an ecosystem, measured in this study by losses in vegetation biomass. It was found that fuel load-related variables, along with dryness and wind, are leading to increased severity. 

Nearly 60 percent of the fires were caused by human activity such as arson, vehicles, power lines, campfires or unknown causes, while lightning sparked the rest. However, the lightning-sparked fires burned more than five times the area burned by human-caused fires.

“Extreme weather conditions are certainly playing a role, but climate change isn’t driving all the change we’re seeing,” said Safford. “Fuel loads played a major role in driving fire severity patterns in forested landscapes in 2020, like in other years. High fuel loads are due mostly to human management decisions over the last century or more, and we can do something about this issue.”

Recent agreements between the state and U.S. Forest Service that seeks to increase fuel-reduction activities, and the California Wildfire and Forest Resilience Action Plan appear promising.  But, the researchers urge that “there is no time to lose.”

The research is published in the journal Global Ecology and Biogeography.

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By Katherine Bucko, Earth.com Staff Writer