A group of climate scientists, led by Swain, published a study on Thursday in the journal Nature Reviews that found what they call “hydroclimate whiplash” — fast swings between alarmingly wet and seriously dry weather — is expanding globally.
The phenomenon has grown up to 66% since the mid-20th century, and the authors expect it to nearly double at 3 degrees Celsius of warming above pre-industrial levels. Average global temperatures could surpass a 1.5 degrees Celsius rise in the next five years.
“I’m still hoping we won’t get there at all, but we are right now still on a path to essentially double the amount of warming we’ve already seen,” Swain said.
The team found that a warmer atmosphere has a greater capacity to hold water vapor and store that moisture for longer before it bursts out of clouds as rain and snow. This can create longer dry periods and more intense precipitation.
As a result, global warming deepens droughts, increases storms or a season’s flood potential, and exacerbates wildfire risk, which is a big deal for California, which is already characterized by a boom-and-bust water cycle. The team describes this phenomenon as hydroclimate whiplash.
“It means that California’s already volatile hydroclimate is likely to become even more so, which makes water management even more difficult,” Swain said.
Whiplash increases fire risk
The wildfires burning in Southern California are a prime example of how the changing climate can exacerbate the impact of a swing between wet and dry conditions, according to study coauthor and UC Merced climatologist John Abatzoglou.
Wet conditions encourage the growth of grasses and shrubs, and if a dry period follows, wildfires can flourish. An errant spark and strong winds can light up a mountainside or neighborhood.
“Warmer air can basically pull more water out of plants and the soil, and that’s one ingredient that sets the stage for fire in our forests,” Abatzoglou said. “We’re essentially adding fuel to the fire.”
Much of Southern California experienced its driest start to the water year following a period of record warmth and two back-to-back wet years. Grasses and chaparral have grown to nearly double their regular rate. The preexisting conditions and strong winds caused the fires to explode out of control.
He said the study’s indicators would have categorized Southern California as unusually wet earlier this year.
“Now, like nine months later, they’re unusually dry,” he said. “They’ve got a pretty significant Santa Ana wind bearing down on them, and they’ve already had several significant fires this fall.”
Swain notes that climate change has deepened fire seasons into the winter months in Southern California. This is problematic because natural offshore winds usually occur during this period. When strong winds overlap with dry vegetation, “dangerous wildfire conditions can develop.”
“This, ultimately, is the key climate change connection to Southern California wildfires,” he said.
The Palisades Fire blows smoke over Santa Monica Beach on Jan. 8, 2025, in Santa Monica, Los Angeles County. Fueled by intense Santa Ana Winds, the Palisades Fire has grown to over 2,900 acres and 30,000 people have been ordered to evacuate while a second major fire has emerged near Eaton Canyon and Altadena. (Tiffany Rose/Getty Images)
Defining hydroclimate whiplash
The scientists reviewed 202 peer-reviewed climate studies, and Swain said they went “beyond what’s in the existing literature by formalizing the term hydroclimate whiplash, defining the phrase in two ways: subseasonal and interannual. The first describes rapid transitions between dry and wet conditions within a three-month season, and the second describes whiplash on a year-to-year scale.
The team, which included scientists from two countries and across the U.S., found that three-month-scale observations of hydroclimate whiplash are increasing on the high end of the climate model range and that longer-term episodes of hydroclimate whiplash are falling within what climate models have predicted so far.
“That might tell us something about why it feels like we are just getting this unrelenting sequence of wet and dry extremes alternating back and forth,” Swain said.
The authors also coined a new term: expanding atmospheric sponge, referring to the growing ability of the atmosphere to absorb water and later release it as precipitation. Scientists found that for every degree Celsius the planet warms, the atmosphere can hold 7% more water.
