Los Angeles wildfires: Why a wetter atmosphere is making California blazes worse

For years, California has oscillated between torrential rain and dry, tinderbox-like conditions - setting the stage for the fires raging across the Los Angeles area and forcing thousands to evacuate.

Now, a study released Thursday in the journal Nature Reviews shows that this trend is growing worldwide, thanks to warming temperatures and a thirsty atmosphere that pulls water from plants and soils. So-called “weather whiplash” conditions have increased 31 to 66 percent across the globe since the mid-1900s, the researchers found.

“This is really, I would argue, a signature of climate change that is going to be experienced almost everywhere people actually live on Earth,” Daniel Swain, lead author of the paper and a climate scientist at UCLA, said in an interview.

Under normal conditions, the atmosphere acts as a sponge - soaking up water from land and oceans and wringing it out in the form of rain or snow. But as the climate warms, that atmospheric sponge increases exponentially, sucking up even more water. For every 1 degree Celsius rise in global average temperature, the atmosphere can hold 7 percent more water vapour.

Scientists have long pointed to this phenomenon as a reason for extreme precipitation, such as the rains that devastated North Carolina during Hurricane Helene last year. But the new paper argues that it can also set the stage for devastating droughts and wildfires.

As the size of that “sponge” increases, the atmosphere can suck more and more water from soils and land - drawing out any excess moisture and gathering it in the air. That leaves trees, brush and other vegetation dry and ready to burn.

Swain said Southern California is experiencing one of these whiplash events. A heavy wet season in the winter of 2022-2023 spurred the growth of grass and brush, which then dried out quickly in summer 2024 as the weather became hot and arid. “There was a bunch more fuel for potential fires to come, and now we’ve kiln-dried it, and we’re getting a big wind event in January,” Swain said. “And it still hasn’t rained.”

“It’s clear from the devastation caused by the current wildfires in L.A. that rapid changes in the volatility of precipitation and evaporation can have a large impact,” Brian Hoskins, a meteorologist who chairs the Grantham Institute at Imperial College London and was not involved in the study, said in an email.

California and parts of the U.S. Southwest have always experienced some form of whiplash; dry seasons followed by wet ones are part of the local climate. But the study analyzed changes in what scientists call the Standardized Precipitation Evapotranspiration Index, which tracks drought and wet conditions. The researchers observed the magnitude of shifts in that index from the mid-19th century to today.

That index showed that global whiplash, measured in three-month periods, has increased by 31 to 66 percent. Year-to-year whiplash, meanwhile, has increased by 8 to 31 percent.

“This is an excellent review of recent studies that address the concept of weather whiplash of various types,” Jennifer Francis, senior scientist at the Woodwell Climate Research Center, said in an email. Francis, who was not involved in the study, noted that the switch from wet to dry conditions in the Southwest occurred about eight months ago - meaning that the whiplash helped create the fuel for the fires but cannot be directly blamed for the blazes themselves.

“But if it does flip from the existing drought to prolonged rains, it could spell trouble to fire-scorched areas,” she added. “They are highly susceptible to flooding and mudslides.”

For now, the Los Angeles area is still burning - and as temperatures warm, it could get worse. For every degree that the planet warms, Swain noted, the shifts will become more and more extreme.

Diana Leonard contributed to this report.

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