The devastating wildfires that have ravaged Southern California have erupted following a dramatic shift from a wet to a very dry climate – a phenomenon scientists describe as hydroclimate whiplash.
New research shows these sudden changes from wet to dry and dry to wet, which can fuel wildfires, floods and other hazards, are increasing and intensifying due to human-induced climate change.
“We're in a whiplash event right now, wet-to-dry, in Southern California,” said Daniel Swain, the UCLA climate scientist who led the study. “Evidence shows that hydroclimate whiplash is already increasing due to global warming, and further warming will bring about an even greater increase.”
The extreme climate change over the past two years in Southern California is one of the most dramatic changes that scientists around the world have documented in recent years.
Unusually wet winters in 2023 and 2024 fed brush and grass growth on hillsides throughout the region, followed by a cold winter. warm and rainless weather from the spring that has left boiled greens all over the Los Angeles area.
Since October, most of Southern California has been baking in dry conditions. This unusual whiplash in weather has increased the risks of the kind of extreme wildfires that have been fueled by strong winds this week, Swain said.
“This whiplash sequence in California has increased fire risk twofold: first, by greatly increasing the growth of flammable grass and brush in the months leading up to the fire season, and then by setting it at much higher rates,” Swain said.
“Climate change is already bringing hotter and drier fire seasons to Southern California that continue into the winter months,” he said. “This is very problematic because strong coastal winds usually occur in late autumn and winter in this part of the world. When such strong winds pile up with very dry vegetation, as is the case now, there can be very dangerous wildfire conditions.”
As the burning of fossil fuels and rising levels of greenhouse gases increase temperatures, Swain and other scientists predict that extreme climate change will continue to become more frequent and erratic, with rain increasingly concentrated in short, intense bursts, interspersed with more severe dry spells.
In their study, published Thursday in the journal Nature Reviews Earth & Environment, the researchers examined climate records around the world and found that hydroclimate whiplash events have already increased by 31% to 66% since the mid-1900s, and are likely to increase further. of double the situation. when the world reaches 3 degrees C, or 5.4 degrees F, of warming.
The researchers said that human-caused climate change is causing the increase, and it is happening because with each additional degree of warming, the atmosphere is able to absorb and release more water. Swain and his colleagues liken this effect to an expanding “atmospheric sponge” that can absorb more water, leading to more severe floods and droughts.
“The problem is that the sponge is getting bigger, like compound interest in the bank,” Swain said. “The growth rate increases with each fraction of the warming rate.”
Swain and his eight co-authors said this extreme variability brings greater risks of dangerous wildfires, floods, landslides and disease outbreaks.
A vineyard remains inundated in the San Joaquin Valley after a series of historic storms.
(Robert Gauthier / Los Angeles Times)
California naturally experiences the world's most dramatic transition between very wet and dry periods. And with more warming, scientists are designing a scenario to see these changes become even more extreme.
The scientist also pointed out another recent example of whiplash in California. Immediately after the severe drought of 2020-22, the country was hit by a series of large atmospheric river storms in 2023 that brought heavy rains and historic amounts of snow, leading to floods and landslides.
Among other examples, scientists point to heavy rains and floods in East Africa in 2023, followed by a long drought that destroyed crops and displaced people.
“Increasing hydroclimate whiplash may be one of the most global changes in a warming world,” Swain said.
Another study found climate change to be the leading cause drought that is getting worse in the western USthat wildfire weather is like that which happens oftenand that global warming has increased wildfire risk.
Adapting to these extreme conditions in California and elsewhere, the researchers say, will require changes in water management practices and infrastructure to plan for both drought and flooding rather than treating them as separate hazards. Another way, they say, is to do it replace natural floods absorbing high runoff from light storms, reducing flood risks while recharging groundwater.
Because increasing climate change is associated with a variety of related risks, scientists say there is an “urgent need for disaster management, emergency preparedness, and infrastructure development” to contain the growing risks of these “degrading impacts.”
The findings also underscore the importance of efforts to limit global warming, Swain said. “The less warming there is, the less hydroclimate whiplash we're going to see.”
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