‘Loading the dice’: Climate crisis could increase wildfires in Southern California | California


A The convergence of hazardous weather, exacerbated by the climate crisis, has set the stage for Southern California to see an increase in catastrophic wildfires in the coming decades, according to a new study.

Southern California, home to 23 million people, has been largely spared the kind of extreme escalation of the fires in the upstate, but models developed by researchers at the University of California, Los Angeles predicted that would change.

Wildfires in Southern California are often sparked by dry winds, low humidity and high temperatures, and the climate crisis is creating the perfect conditions for them to burn hotter, faster and more frequently. Analyze data from 49 climate stations scattered across the southern coast from Santa Barbara to San Diego, the UCLA study found the region could see a doubling of what scientists call “great fire days” by 2100 if greenhouse gas emissions are not reduced.

Even in a more moderate scenario, where heating is slowed, the researchers’ models showed a 60% increase in high-risk days compared to the end of the 20th century.

“Things are going to get worse,” said Glen MacDonald, a UCLA geography professor and lead author of the study.

The researchers analyzed a range of variables that can increase fire risk and found that certain climatic characteristics – particularly air dryness – typically determine when the biggest fires break out. “From there, we found that you could kind of predict when you were going to have your big fire probability in Southern California,” MacDonald said.

After determining the patterns most associated with wildfires, they modeled how those patterns might change in coming decades. They found that not only would the days become drier, but those days would begin to appear earlier in the spring and stay later in the fall, “thereby extending the likelihood to a greater part of the year”, a- he added. They discovered that these high-risk days would likely be going from the 36 days per year documented in the 1970s to the end of the 1990s to 71 days per year in 2070.

These conditions will not only produce more fires, they will also affect fire behavior, making them more destructive and harder to contain.

Southern California landscapes, which are dominated by grasslands and shrublands rather than tall forests, burn and recover differently from their northern neighbours. Decades of land mismanagement and suppression of Indigenous prescribed burning practices have also left northern California forests overcrowded and primed for bad burns – a less common problem in the south.

That’s part of why, MacDonald says, regions have had such different experiences with wildfires. “It’s not like climatologically that we’ve dodged the bullet – but we just haven’t seen the same impact that we see in the more remote areas of northern California and the Sierra Nevada in those forest systems. .”

That doesn’t mean the rest of the state will be spared. A separate study published last year, led by researchers at the University of California, Irvine, looked at temperatures in the Sierra Nevada Range. during 450 fires that broke out there between 2001 and 2020. Their analysis shows that as warming worsens and temperatures continue to climb, fires in the Sierra Nevada could increase by 20% or more over the next 20 years. The amount of land burned will increase even more sharply, increasing by 25% by the 2040s.

The Alisal Fire burned over 16,801 acres in October 2021. Photo: Xinhua/Rex/Shutterstock

“Wildfires are really sensitive to small changes in temperature,” says Aurora Gutierrez, project specialist in the UCI’s Department of Earth System Sciences and lead author of the Sierra Nevada study. The researchers found that for every 1°C (1.8°F) increase in temperature, the risk of fire increases by up to 22%. Over the next two decades, the region expects temperatures to rise by 2°C (3.6°F).

“When it’s hot for a long time, it leads to these megafires that resist fire suppression practices,” Gutierrez says. “In extreme conditions like this, anything that will burn will burn – and there’s not really much you can do to stop it.”

The fires are already exhibiting more extreme behavior, adding new challenges to containment efforts.

A new phenomenon, documented in a study published Wednesday and led by MacDonald’s colleagues at UCLA, is that fires are more likely to burn overnight. The study found that, globally, nighttime fires have increased by 7.2% in intensity over the past two decades thanks to hot, dry conditions that persist after sunset, closing what was once a window. essential to tame the flames.

While MacDonald sees these results as a clear call for immediate action to reduce emissions, he stressed that the models show predictions, not guarantees. There are still ways to avoid a future with even more catastrophic wildfires.

“What we see with the climate system is that we’re pounding the dice,” MacDonald says. “It’s a roll of the dice, but we’re loading them with more and more days where you have this high probability of fire and that spark is more likely to happen when it’s really going to cause damage.”


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