A wicked convergence of blustery wind and prolonged drought has prompted devastation in Southern California, as wildfires in Los Angeles have killed at least 28 people and destroyed more than 16,000 structures. According to a new World Weather Attribution analysis, this grave toll was caused partly by humankind’s burning of fossil fuels.
The hot, dry, windy weather driving the fires was made 1.35 times more likely by human-caused climate change, while the lack of rainfall in preceding months may have been made 2.4 times more likely, the analysis released January 28 shows.
“All the pieces were in place for a wildfire disaster — low rainfall, a build-up of tinder-dry vegetation and strong winds,” UCLA hydroclimatologist Park Williams said in a statement.
Southern California’s fire season typically ends when rainfall arrives in October, November or December. But a paucity of precipitation in late 2024 prolonged the drying of the region’s vegetation, priming the landscape to burn. The drawn-out dryness lingered long enough to coincide with a powerful showing of the Santa Ana winds — a seasonal phenomenon in which hot, arid air from inland desert areas blows toward the California coast. Upon arriving in the City of Angels, Santa Ana winds reaching up to 160 kilometers (100 miles) per hour further desiccated the area’s shrublands, fanned the flames of active blazes and spread embers through the air.
Keen to measure the influence that climate change had on these fire conditions, researchers with World Weather Attribution, or WWA, compared the probability of occurrence with and without modern climate warming. Since 2014, WWA researchers have used local weather data and climate simulations to produce dozens of reports estimating how much climate change has affected the probability and intensity of extreme weather events.
For the new study, the WWA team drew from decades’ worth of data on temperature, relative humidity, wind speed and precipitation in Southern California to conduct several analyses of how hot, dry and windy conditions varied daily from year to year. The researchers also looked at how October-December rainfall patterns varied between years and when drought conditions ended each year.
Timing overlap
As climate change continues to warm the planet, arid weather conditions that desiccate vegetation are becoming more likely to coincide with powerful Santa Ana winds — seasonal winds that blow hot, dry air from inland desert areas to the California coast. The convergence of these factors increases the risk of wildfires.
Change in how drought conditions align with peak Santa Ana winds
After comparing the data to nearly a dozen different climate simulations, the researchers concluded that climate change made the warm, arid and windy conditions in January about 35 percent more likely and 6 percent more intense compared with the preindustrial period, which was on average about 1.3 degrees Celsius cooler than today. Such fire-prompting conditions are expected to occur once every 17 years on average, the researchers report. But if global warming rises to 2.6 degrees C above preindustrial levels — which is projected to occur by 2100 — the conditions will be about 1.8 times more likely than today.
Additionally, the Los Angeles dry season now lasts roughly 23 days longer than in preindustrial times, the data indicate. This suggests that human-caused climate change is helping to delay the end of drought conditions, thereby promoting an overlap with the Santa Ana wind season.
The researchers were unable to clearly simulate the link between climate change and the low seasonal rainfall rates or lengthening dry season using computer models, partly due to the relatively small size of the Los Angeles area compared with the broad level of detail in the models. That meant the team could not definitively blame climate change alone for the diminished rainfall leading up to the fire, or for the extra 23 days of dry conditions.
But other studies that have assessed the broader Southern California region have indicated that climate change is delaying the end of the dry season, climatologist Friederike Otto of Imperial College London said at a January 28 news briefing.
“We can officially say that climate change does play a role in this,” Otto said.