Very hot summer and autumn. An unusually dry winter. Hillsides covered with bone-dry vegetation. and strong Santa Ana winds.
In the mix of conditions that contributed to the most destructive fire in LA history, scientists say a significant ingredient is human-caused climate change.
A team of UCLA climate scientists said: Analysis If you break down the reasons behind vegetation being so dry as wildfires raged in Southern California this week, global warming may have contributed to a quarter of the drought, one of the factors fueling the fire's explosiveness. The high heat in summer and dry bushes and grasses in the mountains help burn that fuel more vigorously when they burn.
Without the higher temperatures brought by climate change, the fires would have been more intense, but they would have been “slightly smaller and less intense,” the scientists said.
The conditions that made such catastrophic fires possible were like three switches that all flipped at once, said climate scientist Park Williams, who prepared the analysis with UCLA colleagues Alex Hall, Gavin Madakumbura and others. Climate and Wildfire Research Initiative.
“Those switches were very high fuel loads, unusually dry fuels and an unusually strong Santa Ana wind event,” Williams said. “All of these are mostly due to natural disasters.”
But because all those natural switches line up, “now the atmosphere is warmer because of climate change, and then the fuels are drier than they would have been otherwise, so fires are more intense and bigger than they were. It was different.”
The scientists said that comprehensive studies and studies investigating the impacts of climate change and natural factors take time and prepared their analysis as a starting point for deeper research.
A helicopter drops water on a burning ridge in Brentwood during the Palisades fire Saturday.
(Myung J. Chun/Los Angeles Times)
Williams and his colleagues examined the past two wet winters, which fostered the growth of chaparral and grasses across Southern California. They mentioned that they have studied More intense atmospheric river storms are planned Due to global warming, but so far this trend did not appear in the data The impact of climate change on the past two wet years in the western United States is “highly uncertain.”
They studied unusually dry conditions in Southern California, which had not seen significant rain in eight months. A weather station in Los Angeles recorded only 0.29 of an inch of rain from May 1 to January 8, the second driest since 1877, behind 1962-63, which had 0.15 inches. However, the extent to which climate change may have promoted the unusually long dry spell remains “highly uncertain,” the researchers said.
However, the exceptionally warm summer and fall of 2024 are part of a clear trend toward warmer temperatures due to human-caused climate change, the scientists said.
The summer-autumn season ranked as the region's third-warmest since 1895, and occurred in a year of U.S. government agencies. Global warming is confirmed Since registration began in 1880.
The researchers said the heat in Southern California was partly responsible for the dramatic drop in the “fuel moisture content” of dead vegetation, making it the driest January on record, and that the conditions were “more favorable for wildfires.”
They estimated that abnormal heat accounted for about 25% of vegetation drought, while a lack of rain accounted for the other 75%.
When strong Santa Ana winds blew in on Jan. 7, they brought the final piece to a mix of factors that set the stage for high fire danger, as has sometimes been the case this year.
“The clearest way climate change will affect fires in the western United States and California is through the direct influence of warmer atmospheric temperatures,” Williams said. Previous research And Other studies. “A warm atmosphere is a thirsty atmosphere, so all else being equal, fuels will dry out faster in a warmer world.”
Other scientific studies have found that human-caused warming Also causes severe drought and contribution Large and intense wildfires In the western United States
Still, Williams said, there are important differences between areas where wildfires break out in forests with abundant plant fuel and areas like Southern California, where fires often burn shrubs and grasses.
California as a whole has seen a trend toward larger wildfires in recent years. But in coastal Southern California, the data show that there hasn't been a trend toward larger fires over the past four decades, and the number of fires has actually decreased during this period — perhaps because people are accidentally more careful. A shift toward climates or drier average conditions has made plants rarer over the years, Williams said.
“What you see is most years there's no fire, and then some years there's a lot of fire,” Williams said. “Every once in a while, Southern California gets unlucky and all three of those switches get flipped at once.”
Some studies have predicted drier ecosystems in the West, like much of Southern California. Probably less fire is seen on average In a hotter, drier future, more drought reduces the amount of flammable vegetation. However, Southern California is still likely to have wet years that bring more plant growth. As these fires showed, Williams said, “if the previous year was wet, more fires should be expected the following year.”
“In those rare years when all the pieces come together to promote wildfires, the warming of the atmosphere due to human-caused climate change can make many fuels drier than they would otherwise be,” Park said. “This would allow fires during these episodic years to grow larger and more intense than under cooler conditions.”
The cause of the fire is under investigation, and scientists have noted that with the lack of natural sources of ignition this year, the fire is almost certain to occur. Initiated by human activities In some way – sparks from power lines, bursting of firecrackers, arson or any other reason.
The UCLA team prepared the analysis during tense days as they watched losses unfold, from friends and colleagues leaving or homes burning down.
This week, professors are teaching the following classes online University result The campus has poor air quality due to wildfire smoke.
“It's basically a natural disaster. Once you have ignition, we live in a place with very extreme events,” said Hall, another climate scientist who prepared the analysis.
“Climate change is juicing it a little bit. We can't quite quantify it, but it's something,” Hall said. “We know that the heat dried out the plants. We know that a certain part of the lack of moisture we had when the fire started could be responsible for that unusual heat.
Without the influence of climate change, “it probably would have been somewhat smaller and easier to fight,” he said.
A more in-depth look at the influence of global warming will involve studies that further explore the complex dynamics of fires, weather and rising temperatures, Hall said.
These and other attribute studies are growing in California, Hawaii and other states Sue the oil companiesIt seeks billions of dollars in compensation for the effects of burning fossil fuels.
Warmer summer temperatures and drying vegetation are trends seen in recent decades linked to human-caused warming, said climate scientist Julie Kalansky, deputy director of the Center for Western Weather and Water Extremes at UC San Diego's Scripps Institution. Oceanography.
She pointed out Research Higher temperatures in recent decades show increased “evaporative demand,” drawing more moisture from land in the western U.S., the authors point to the need to plan for increased wildfire risks.
As for the LA fires, Kalansky said more studies will be needed to better understand the contribution of climate change and “to be able to put some more concrete numbers on it.”
The UCLA scientists wrote that as climate change continues, “more intense wildfires are expected when all the other conditions necessary for fire occur.”
They called for focusing wildfire mitigation efforts “around the factors we can control and the damage we can prevent,” such as preventing ignition during fire weather, adopting strategies to prevent homes from burning easily, and planning development in low fire risk zones.
Scientists can play an important role in identifying fire-prone areas that should be avoided because of their location or exposure to flammable vegetation, Williams said.
“In the long run, these kinds of extreme events are happening here, and when all the factors are aligned, that should guide decisions about where to rebuild,” he said. “In some places, when the fuels come back, the fire risk will be very high again.”
