You can fight fire with fire, even in the flammable forests of the western US.
According to an analysis of California鈥檚 record-breaking 2020 fire season, intentionally burning land can reduce the severity and amount of smoke from wildfires that burn those areas later on, even when accounting for smoke from the intentional fires themselves. 鈥淲e show that there is a net benefit,鈥� says at Stanford University in California.
The idea of 鈥減rescribed burning鈥� is nothing new. For millennia, Indigenous societies in California commonly set fires on purpose to manage vegetation. But centuries of fire suppression efforts that followed European colonisation have led to forests filled with unburnt vegetation. Heat and drought from climate change have further primed these forests to burn in ever-larger blazes. Now, fire officials in the western US are increasingly looking at prescribed burns to limit wildfires and their smoke.
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To see how prescribed burns would work in California鈥檚 tinderbox-like forests, Kelp and his colleagues looked at satellite images of fire severity and smoke from 186 areas where prescribed burns took place, which were later burned during California鈥檚 extreme 2020 fire season.
They found that, on average, wildfires were around 15 per cent less severe in areas that had prescribed burns compared with nearby areas that had not been treated. These pre-burned areas also generated about 14 per cent less smoke, even after factoring in the smoke from the initial prescribed burn.
Setting these strategic blazes was also more effective than other fuel-reduction methods, like mechanically thinning out forests. That is mainly because the intentional burns clear out more of the fine fuel and brush, says Kelp. 鈥淣one of this was a given,鈥� he says.
Based on these results, the researchers estimate that intentionally setting fire to 400,000 hectares (one million acres) of California each year would lead to a net reduction in wildfire smoke of around 650,000 tonnes over the next five years, assuming most of that area was burned again within eight years. That is equivalent to cutting wildfire smoke from the state鈥檚 2020 season in half.
at the University of California, Los Angeles, who wasn鈥檛 involved with the study, says this could help address 鈥渧alid air quality-related concerns鈥� around the state鈥檚 efforts to expand prescribed burns.
State and federal agencies conducted prescribed burns on 30,000 hectares (80,000 acres) in California in the past fiscal year, more than twice as much as usual, and they to scale up again in 2025, treating around 160,000 hectares (400,000 acres) with 鈥渂eneficial fire鈥�.
However, even if prescribed burns would reduce overall smoke, more work is needed to understand how communities near prescribed burn areas may be disproportionately affected, says Schollaert. The pattern of frequent, low-intensity smoke from prescribed burns may also have different health effects than infrequent, but intense smoke exposure from wildfires.
There are also regulatory, cultural and political barriers to prescribed burning, given the risk of fires growing out of control and concerns about increased exposure to smoke from the prescribed burns. 鈥淧eople are afraid of fire, and rightly so,鈥� says Kelp.
He says the strategy doesn鈥檛 work as well in densely populated neighbourhoods such as those destroyed in the LA fires this month, where the proximity of people and property makes it more challenging to pull off prescribed burns.
EarthArXiv
