Climate Scientists Warn of Growing Whiplash Effect on Weather Patterns

Californians are all too familiar with flip-flopping weather extremes.

The massive wildfires currently burning in Southern California followed two years of excessive rainfall, the hottest summer on record, major flooding that re-filled a historic lake in the Central Valley, the most severe drought in recorded history, and so on, all in the last decade.

New research cements the idea that California’s weather whiplash is increasing as the atmosphere warms due to human-caused climate change.

“I see the last decade as a preview of what we should expect to see more of,” said Daniel Swain, a climate scientist with UC Agriculture and Natural Resources and UCLA. Except that “the wettest wets and the driest dries we’ve seen recently are not the wettest wets and the driest dries we will see in the coming decades.”

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.

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.

Noah Diffenbaugh, a Stanford climate scientist and coauthor, said the atmosphere is like a yellow kitchen sponge that increases in size as it warms.

“When you wring the sponge out, it’s going to have more water getting wrung out of it,” he said. “But at the same time, it will take more water to fill that sponge.”

In some sense, he said anthropogenic climate change creates “a more thirsty” atmosphere.

“It’s kind of this paradox that as the atmosphere gets warmer, both the amount of water vapor in the atmosphere can increase, and the deficit of water vapor in the atmosphere can also increase exponentially,” Diffenbaugh said.

You don’t have to look too far in the past to see an example of how a super wet period broke up a severe drought. California’s stormy winter of 2022–23 dismantled a three-year drought and is an example of interannual hydroclimate whiplash.

“The silver lining is that we will still get those wet years,” Swain said. “The water did come. It just didn’t come in a nice, gentle, convenient way.”

No more chasing average water years

Abatzoglou said human-caused climate change will increase extremes, but average precipitation totals may not change “a heck of a lot.”

Abatzologu suggests that the state’s leaders plan for “changes in extremes” from wet to dry or vice versa instead of average precipitation totals. While the study shows “a little bit of a shift more toward potentially wetter periods in the future,” he said the extremes are dangerous, as they can cause flooding or drying out issues.

All the study authors, including Abatzolgou, Diffenbaugh, and Swain, have experienced extreme weather whiplash in recent years. Swain hosts weekly YouTube office hours dissecting hydroclimate whiplash, primarily along the West Coast. He discusses sudden changes in weather patterns, like tornados, and has detailed how the state moved from drought to deluge in recent years.

Overall, Swain describes hydroclimate whiplash, which Californians live with year in and year out, “as the flavor of climate change in California” that residents must endure unless the world reduces global emissions that cause atmospheric warming.