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Floods, droughts, then fires: Hydroclimate whiplash is speeding up globally
New research links intensifying wet and dry swings to the atmosphere's sponge-like ability to drop and absorb water
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Key takeaways
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Los Angeles is burning, and accelerating hydroclimate whiplash is the key climate connection.
After years of severe drought, dozens of atmospheric rivers deluged California with record-breaking precipitation in the winter of 2022-23, burying mountain towns in snow, flooding valleys with rain and snow melt, and setting off hundreds of landslides.
Following a second extremely wet winter in southern parts of the state, resulting in abundant grass and brush, 2024 brought a record-hot summer and now a record-dry start to the 2025 rainy season, along with tinder-dry vegetation that has since burned in a series of damaging wildfires.
This is just the most recent example of the kind of “hydroclimate whiplash” – rapid swings between intensely wet and dangerously dry weather – that is increasing worldwide, according to a paper published Jan. 9 in Nature Reviews.
“The evidence shows that hydroclimate whiplash has already increased due to global warming, and further warming will bring about even larger increases,” said lead author Daniel Swain, a climate scientist with UC Agriculture and Natural Resources and UCLA. “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 fire season, and then by drying it out to exceptionally high levels with the extreme dryness and warmth that followed.”
Global weather records show hydroclimate whiplash has swelled globally by 31% to 66% since the mid-20th century, the international team of climate researchers found – even more than climate models suggest should have happened. Climate change means the rate of increase is speeding up. The same potentially conservative climate models project that the whiplash will more than double if global temperatures rise 3 degrees Celsius above pre-industrial levels. The world is already poised to blast past the Paris Agreement's targeted limit of 1.5 C. The researchers synthesized hundreds of previous scientific papers for the review, layering their own analysis on top.
Anthropogenic climate change is the culprit behind the accelerating whiplash, and a key driver is the “expanding atmospheric sponge” – the growing ability of the atmosphere to evaporate, absorb and release 7% more water for every degree Celsius the planet warms, researchers said.
“The problem is that the sponge grows exponentially, like compound interest in a bank,” Swain said. “The rate of expansion increases with each fraction of a degree of warming.”
The global consequences of hydroclimate whiplash include not only floods and droughts, but the heightened danger of whipsawing between the two, including the bloom-and-burn cycle of overwatered then overdried brush, and landslides on oversaturated hillsides where recent fires removed plants with roots to knit the soil and slurp up rainfall. Every fraction of a degree of warming speeds the growing destructive power of the transitions, Swain said.
Many previous studies of climate whiplash have only considered the precipitation side of the equation, and not the growing evaporative demand. The thirstier atmosphere pulls more water out of plants and soil, exacerbating drought conditions beyond simple lack of rainfall.
“The expanding atmospheric sponge effect may offer a unifying explanation for some of the most visible, visceral impacts of climate change that recently seem to have accelerated,” Swain said. “The planet is warming at an essentially linear pace, but in the last 5 or 10 years there has been much discussion around accelerating climate impacts. This increase in hydroclimate whiplash, via the exponentially expanding atmospheric sponge, offers a potentially compelling explanation.”
That acceleration, and the anticipated increase in boom-and-bust water cycles, has important implications for water management.
“We can't look at just extreme rainfall or extreme droughts alone, because we have to safely manage these increasingly enormous influxes of water, while also preparing for progressively drier interludes,” Swain said. “That's why ‘co-management' is an important paradigm. It leads you to more holistic conclusions about which interventions and solutions are most appropriate, compared to considering drought and flood risk in isolation.”
In many regions, traditional management designs include shunting flood waters to flow quickly into the ocean, or slower solutions like allowing rain to percolate into the water table. However, taken alone, each option leaves cities vulnerable to the other side of climate whiplash, the researchers noted.
“Hydroclimate in California is reliably unreliable,” said co-author John Abatzoglou, a UC Merced climate scientist. “However, swings like we saw a couple years ago, going from one of the driest three-year periods in a century to the once-in-a-lifetime spring 2023 snowpack, both tested our water-infrastructure systems and furthered conversations about floodwater management to ensure future water security in an increasingly variable hydroclimate.”
Hydroclimate whiplash is projected to increase most across northern Africa, the Middle East, South Asia, northern Eurasia, the tropical Pacific and the tropical Atlantic, but most other regions will also feel the shift.
“Increasing hydroclimate whiplash may turn out to be one of the more universal global changes on a warming Earth,” Swain said.
In California this week, although winds are fanning the extreme fires, it's the whiplash-driven lack of rain that suspended Southern California in fire season.
“There's not really much evidence that climate change has increased or decreased the magnitude or likelihood of the wind events themselves in Southern California,” Swain said. “But climate change is increasing the overlap between extremely dry vegetation conditions later in the season and the occurrence of these wind events. This, ultimately, is the key climate change connection to Southern California wildfires.”
Under a high warming scenario, California will see an increase in both the wettest and driest years and seasons by later this century.
“The less warming there is, the less of an increase in hydroclimate whiplash we're going to see,” Swain said. “So anything that would reduce the amount of warming from climate change will directly slow or reduce the increase in whiplash. Yet we are currently still on a path to experience between 2 degrees and 3 degrees Celsius of global warming this century — so substantial further increases in whiplash are likely in our future, and we really need to be accounting for this in risk assessments and adaptation activities.”
The research was supported with funding from The Nature Conservancy of California and the Swiss National Science Foundation.
Climate scientist Daniel Swain joins UC ANR
“We are very excited to have Daniel Swain join UC ANR,” said Glenda Humiston, UC vice president for agriculture and natural resources. “He brings a unique blend of skills and expertise that are crucial to meet the challenge of climate change, here in California and across the globe. Daniel's research – and his ability to clearly explain the latest findings in climate science – can equip fellow academics, policymakers and communities with the vital tools they need to forge effective and sustainable solutions.”
Swain is known for his exceptional science communication skills, explaining weather and climate in terms easily understood by the public.
“I spend a great deal of time engaging directly with the public in California and beyond on weather, climate and disaster-related topics, so I'm thrilled to be joining UC ANR—where broad dissemination of research-based information is a key part of the mission,” Swain said. “I'm grateful for ANR's support for my unusual hybrid climate research and science communication role, and look forward to helping expand ANR's virtual and statewide reach in the years to come.”
In November, Swain was named one of Vox's Future Perfect 50 – “the thinkers, activists and scholars working on solutions to today's (and tomorrow's) biggest problems.” Vox wrote: “Our communities and institutions are largely unequipped to fully understand, let alone deal with, the impacts of climate change. That's where climate experts should, theoretically, come in. But knowing the science is one thing – being able to effectively communicate it is a whole other ballpark. Climate scientist Daniel Swain is that desperately needed liaison.”
On his widely read Weather West blog, Swain has been sharing his perspectives on California weather and climate since 2006. He hosts regular “virtual office hours” for the public on YouTube. On X/Twitter, he has more than 101,000 followers.
The “Weather Whisperer” fields hundreds of calls from reporters every year and has been the single most-quoted expert in recent years at UCLA, where he was a climate scientist in the Institute of the Environment and Sustainability. Last year, when Swain was seeking institutional support that would allow him to do science communication as well as research, a Los Angeles Times columnist wrote, “I certainly rely on Swain and other scientists to tell environmental stories.”
The term "Ridiculously Resilient Ridge" was coined in 2013 by Swain on his Weather West blog to describe the large, formidable high-pressure mass that persisted over the West Coast during winter and diverted storms away from California, contributing to the state's 2013-2017 drought.
Before joining UC ANR, Swain, who grew up in the Bay Area, was at UCLA and held a concurrent appointment as a research fellow in the Capacity Center for Climate and Weather Extremes at the NSF National Center for Atmospheric Research since 2018. While holding a 100% appointment with UC ANR, he will maintain his associations with UCLA and NSF NCAR.
Swain holds a Ph.D. in Earth system science from Stanford University and a bachelor's degree in atmospheric science from UC Davis.
He will be the keynote speaker at the California Irrigation Institute's annual conference on Jan. 27 in Sacramento. His talk is titled “Drier and Wetter in 21st Century California? Managing Increasing Hydroclimate Whiplash in a Warming World.”
In addition to posting on his blog at weatherwest.com, Swain is also on Twitter/X @Weather_West, Bluesky https://bsky.app/profile/weatherwest.bsky.social, YouTube https://youtube.com/@weatherwest, Threads https://threads.net/@weather.west and Mastodon https://mastodon.social/@weatherwest.
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Landscaping with wildfire exposure in mind can protect homes
What can Californians do to improve the chances that their homes will survive a wildfire? Simple actions taken around the home can substantially improve the odds that a home will survive wildfire, according to UC Cooperative Extension advisors.
During wildfire, structures are threatened not only by the flaming front of the fire, but also by flaming embers that are lofted ahead of the fire front and land on fuels such as vegetation or mulch next to the house, igniting new fires. Traditional defensible space tactics are designed to mitigate threats from the flaming front of the fire but do little to address vulnerabilities to embers on or beside a structure.
“Without attention to ember-related risks, defensible space efforts only address a portion of the wildfire threat—especially during wind-driven fires in which embers are the primary source of fire spread,” said co-author Yana Valachovic, UC Cooperative Extension forest advisor in Humboldt and Del Norte counties.
An updated University of California Agriculture and Natural Resources publication describes how embers, radiant heat, and direct flame contact ignite buildings and shares low-cost actions residents can take to create effective defensible space.
“The new publication is up-to-date with the changes in California's defensible space guidance, and it addresses Zone Zero, or the missing ingredient, in defense space,” Valachovic said. “The publication also provides a thoughtful discussion of plant lists and their limitations.”
The odds of a home surviving a wildfire can be substantially improved through careful attention to three things: careful design and maintenance of landscaping; awareness and management of combustible materials on the property such as leaf litter, wood piles and lawn furniture; and incorporation of fire- and ember-resistant construction materials with appropriate installation and maintenance.
“You don't have to spend a lot to protect your home from these wildfire threats,” said Valachovic.
Zone Zero, the area within five feet of the house, is the most vulnerable area around the home, according to the UC Cooperative Extension researchers. “During wind-driven fires, embers are the primary source of fire spread,” Valachovic said.
They recommend removing combustible plants, planter boxes, mulches and wood piles within the five-foot perimeter of the house and beneath attached decks.
“While it may be a radical change, clearing the area next to the house will reduce the risk of ember-caused direct flame contact and radiant heat exposure, which are responsible for many home losses,” she said. “Because embers can accumulate at the base of an exterior wall, it is also important to create a six-inch noncombustible zone between the ground and the start of the building's siding.”
Colorful illustrations in the publication depict the three-zone defensible space strategy and show how spacing out trees on a sloped landscape can prevent fire from climbing from tree to tree to reach a house at the top of the slope.
The 12-page “Reducing the Vulnerability of Building to Wildfire: Vegetation and Landscaping Guidance” is available free for download at https://anrcatalog.ucanr.edu/pdf/8695.pdf.
“Landscaping for fire is part of an overall strategy aimed at reducing risk to the home,” said co-author Steven Swain, UC Cooperative Extension environmental horticulture advisor for Marin and Sonoma counties. “To reduce the risk of home loss, start at the house and work out from there,” he recommended.
Swain, Valachovic and Stephen Quarles, UC Cooperative Extension advisor emeritus, are currently updating a publication on retrofitting houses for wildfire resiliency.
Steps for hardening houses against wildfire can also be found at the Fire in California website: https://ucanr.edu/sites/fire/Prepare/Building.
