The devastating wildfires raging across Southern California erupted after weather shifted from wet to bone-dry conditions — a phenomenon scientists describe as hydroclimate whiplash.
New research shows that these sudden wet and dry swings are becoming more frequent and intense due to human-caused climate change, which could exacerbate wildfires, floods and other disasters.
“Southern California is experiencing a wet-to-dry sprain event right now,” said Daniel Swain, a UCLA climate scientist who led the study. “Evidence suggests that hydroclimate whiplash is occurring due to global warming. Already increasing, further warming will bring even greater increases.”
The extreme weather changes in Southern California over the past two years are among many such dramatic swings that scientists have documented around the world in recent years.
Unusually wet winters in 2023 and 2024 nourished scrub and grass on the region’s hillsides, and then came an extreme drought. Warm weather with no rain Vegetation has been dry throughout the Los Angeles area since spring.
Much of Southern California has been in record-dry conditions since October. Swain said this unusual weather change increases the risk of extreme wildfires that will break out this week amid strong winds.
“This whiplash sequence in California doubly increases fire risk: First, it greatly increases the growth of flammable grasses and brush in the months leading up to the fire season, and then it dries out to abnormally high levels,” Swain said. .
“Climate change is already bringing hotter and drier fire seasons to Southern California, which are increasingly extending into the winter,” he said. “This is particularly problematic because of the late fall and winter months in this part of the world. Strong offshore winds are common. When such strong winds overlap with extremely dry vegetation conditions, as is currently the case, very dangerous wildfire conditions can occur.
As the burning of fossil fuels and rising greenhouse gas concentrations push up temperatures, Swain and other scientists predict that extreme weather swings will continue to become more frequent and erratic, with precipitation increasingly concentrated in shorter, more intense bursts. outbreaks, interspersed with more severe drought periods.
In the study published Thursday in the journal Nature Reviews Earth & Environment, researchers examined global weather records and found that hydroclimate whiplash events have increased by 31% to 66% since the mid-1900s, and at some Cases of global warming could more than double to 3 degrees Celsius (5.4 degrees Fahrenheit).
Researchers say human-caused climate change is driving an increase in water, and this is happening because the atmosphere is able to absorb and release more water with each degree of warming. Swain and his colleagues liken the effect to an expanding “atmospheric sponge” that absorbs more water, leading to more severe floods and droughts.
“The problem is that the sponge grows exponentially, just like compound interest in a bank,” Swain said. “For every degree of warming, the rate of expansion increases.”
Swain and eight co-authors said these more dramatic swings bring a greater risk of dangerous wildfires, flash floods, landslides and disease outbreaks.
A vineyard in the San Joaquin Valley was flooded after a series of historic storms.
(Robert Gauthier/Los Angeles Times)
California naturally experiences some of the most dramatic transitions between the world’s wettest weather and drier conditions. As the climate warms, scientists expect these fluctuations to become more extreme.
The scientist also cited another recent example of whiplash in California. Following a severe drought in 2020-22, the state was hit by a series of major atmospheric river storms in 2023, bringing heavy rains and historic snowfall that led to flooding and landslides.
On top of this, scientists point to heavy rains and flooding in East Africa in 2023 after a long drought destroyed crops and displaced people.
“Intensifying hydroclimate shocks may become one of the more pervasive global changes in a warming planet,” Swain said.
Other studies have found that climate change has become a major driver of economic growth. Drought intensifies in western U.S.wildfire weather is occur more frequentlyand global warming has increased Risks of explosive wildfire growth.
Researchers say adapting to these more severe weather extremes in California and elsewhere will require changes in water management practices and infrastructure to respond to droughts and floods rather than treating them as separate hazards. One way, they say, is Restoring natural floodplains Absorb high flows from severe storms, reducing flood risk while recharging groundwater.
Because increased climate volatility is associated with a variety of interconnected hazards, scientists say there is an “urgent need for disaster management, emergency preparedness and infrastructure design” to incorporate the growing risks of these “cascading impacts.”
Swain said the findings also underscore the importance of efforts to limit global warming. “The less warming, the less increase we will see in hydroclimate fluctuations.”
