The Los Angeles fires have become a stark example of the devastating effects of hydroclimate whiplash, as extreme weather patterns fuel increasingly destructive wildfires.
After enduring years of punishing drought, California was inundated by atmospheric rivers during the winter of 2022-2023, bringing record-breaking precipitation, snow-covered mountain towns, and landslides. Yet, this fleeting relief came with a catch. Another wet winter spurred rampant vegetation growth, which, by the scorching summer of 2024 and a bone-dry start to 2025, became tinder for wildfires. The rapid shifts between soaking rains and intense heat highlight the growing unpredictability of hydroclimate extremes and their dangerous consequences for communities and ecosystems.
At the 2025 California Irrigation Institute, Dr. Daniel Swain, a climate scientist with UCLA and UC Agriculture and Natural Resources, gave a presentation on hydroclimate whiplash and what it means for California.
Changing character of precipitation and evaporation in a warming world
Extreme weather events are becoming more frequent worldwide. On average, precipitation across the Earth’s surface increases by about 2-3% for every degree Celsius (or 1.8 degrees Fahrenheit) of warming. The map on the lower left shows mean precipitation, which reflects a mix of increases and decreases in average precipitation depending on the location. The map on the lower right shows projections for changes in extreme precipitation, indicating an increase of 5-10% for each degree Celsius of warming; this map is predominantly green, highlighting a more uniform increase in extreme precipitation.
“Even in places where the average precipitation either doesn’t change very much or perhaps even decreases, we still project quite large increases in the wettest wets, regardless of what happens on average,” said Dr. Swain. “Almost every populated land area on earth will see an increase in the most extreme rain events that occur in a warmer world.”
The other side of the atmospheric coin – evaporation – is likewise important. Even if the relative humidity doesn’t change that much on average and overall stays relatively constant, there is still an increase in the vapor pressure deficit and, therefore, in the atmospheric evaporative demand.
“So as temperatures rise, even if relative humidity does not change at all, there would still be an exponential increase in the thirstiness of the atmosphere,” said Dr. Swain. “This is not a speculative claim at all. It is a fundamental reality of the thermodynamics of air and water in the Earth system.”
This can be demonstrated with climate models, in a greenhouse, using the Clausius–Clapeyron relation equation that dates back to thermodynamic theory from the 1800s – or even a pair of kitchen sponges.
“What it means in practice is that there’s an increased ceiling on the intensity of both precipitation but also evaporation,” he said. “Much as a progressively larger kitchen sponge, if you spill some water on the counter, you wring it out, it will yield more water. Even if you haven’t spilled that water and there’s nothing to absorb with your oversized sponge, it still has that increased capacity to absorb that water, so it’s going to be demanding that water out of its environment, much as the warmer atmosphere does in a warming climate.”
“So in sum, as temperatures rise, both locally and globally, we have an atmosphere that becomes both thirstier when it’s not saturated and not raining, but also capable of much heavier downpours when conditions are right. So when it rains, it pours, literally and increasingly, in a warming climate.”
Dr. Swain led the review paper, Hydroclimate volatility on a warming Earth, that looked at precipitation and evaporation extremes, wildfires, drought, and agricultural impacts and unified some disparate threads floating around in the peer-reviewed literature. “What we find both in assessing over 200 papers that have been written in the last 10 or 15 years, primarily, and in doing our own analysis using the most recent data, are nearly universal increases in projected hydroclimate whiplash on a warming Earth.”
Hydroclimate whiplash as a function of warming
The term “hydroclimate whiplash” describes the rapid shifts between opposing climate conditions, such as from dry to wet or from wet to dry. This phenomenon is mainly driven by the expanding atmospheric sponge, which extends further into the extremes of the water cycle, affecting both dry and wet conditions. As temperatures rise, the projected increases in these shifts are generally more intense, quicker, and become apparent sooner over land. This is because land amplifies warming and increases evaporation rates.
The projected acceleration in the increase in hydroclimate whiplash is between 1-3 degrees Centigrade of global mean warming. “Currently, we’re somewhere around 1.4 in the multi-year average, but we just had a couple of years that were above 1.5,” Dr. Swain said. “We’re not there yet in terms of our long-term benchmark, but we’re getting closer. We’re right in the middle of that range where we would expect this process to start to take off.”
Looking back at data from the 1980s, 1990s, and early 2000s may not be sufficient to predict what is coming next. Recent observed global increases in subseasonal hydroclimate whiplash have been considerably larger than projected by climate models, yet overall warming levels are quite close to predictions.
“Something else is going on,” said Dr. Swain. “We’re not totally sure what it is yet. It could be related to El Nino and La Nina cycles changing a bit differently than had been expected, but that’s still speculative. So, the research continues, but this is not something that is not happening in a warming world. This is something that is occurring and unfolding faster than we had predicted for this point in time. And that leads to some pretty big questions about what might be coming next.”
What’s going on in California?
In California, the annual average precipitation has remained relatively stable over the years. While there has been a slight decrease in precipitation over the past few decades, particularly in Southern California, overall, the trend in annual average precipitation is not significant. The levels of precipitation are not dramatically lower than the historical average.
“However, there is a substantial increase in the variability of California’s hydroclimate over the same period,” said Dr. Swain. “We’ve also seen a pretty robust trend towards longer and more severe drought. So, all of this is unfolded in an environment with no statistically significant decrease in precipitation. So what’s going on here?”
The slide on the right shows the sequence of the past ten years: In 2015, it was a historically severe drought; then two years later, multiple atmospheric rivers caused damage to the spillway at Oroville Dam. That was followed by one of the hottest periods on record in Northern California, and the deadliest and most destructive wildfire, at least until recently, in Butte County that largely destroyed the town of Paradise. Another drought in 2021, and 2023, reservoirs are full again.
“This is how you can have increases in some of the extremes, even if you don’t have any change in the average because, of course, if you have exactly equal and opposite extremes, if you average over a wide enough window, it’s going to look like nothing has changed,” said Dr. Swain.
Weather whiplash contributed to the devastating wildfires in Southern California. There were two very wet winters in Southern California in 2023 and 2024 – the wettest 18-month period on record in some areas. That was followed by the singularly hottest and driest summer on record across the interior and mountain portions of the southern part of the state. The heat persisted into the fall, and Southern California had no precipitation until the end of January after the devastating fires.
“This was the lowest precipitation period on record for Southern California over a 9-10 month period following essentially the wettest 18 month period immediately preceding and with some record heat in between,” he said. “What this produced was a really pronounced wet-to-dry whiplash event. All the abundant precipitation worsened the wildfire situation by producing abundant growth of herbaceous vegetation, grass, and brush. Then it was kiln-dried with the driest period on record, with some record-breaking heat smashed in there. Then we had a really big wind event and the rain still hadn’t arrived, and we saw what happened. But it is precisely that sequence of vegetation growth and then curing that is a signature of wet-to-dry whiplash, so that, in a sense, the fire risk that resulted this year was greater than the sum of its parts. Had that happened in the reverse order, we may not be even talking about this event right now.”
Precipitation in California: A wetter and drier future?
So the answer to the question, is California wetter or drier in a warming world? is both; it just depends on when you look at it and how you measure it. “Our research suggests that from a precipitation perspective, the wettest wets become wetter and the driest dries become drier. Historically, we’ve seen larger increases on the dry extreme side than on the wet extreme side. But we expect that to maybe not fully even out moving forward, but see a better balance. We will see decades with unprecedented wet extremes in the coming years in California. I just can’t tell you exactly which decade that’s going to be and recently, we’ve seen more dry than wet, especially in Northern California.”
He noted instances such as the extraordinary atmospheric river event in Sonoma County and Northern and Southern California, where record-breaking rainfall events occurred within the record-breaking droughts over the past decade.
In Northern California, the primary moisture delivery mechanism is atmospheric rivers. In a warming climate with an expanding atmospheric sponge, the most extreme atmospheric rivers will become even more so, leading to eventually the emergence of historically unprecedented atmospheric rivers.
California’s other “big one” is a statewide flood event; the paleoclimate records show that these have occurred in California every 100-200 years. The last one was in 1862. So the chance of a similar event is possible, even without climate change, and would be disastrous, even given California’s modern flood control.
“In 2018, we published a study that suggested there’s about a 50/50 chance of an 1862-level flood event in the next 40 years, which is higher than you’d expect, and that is, of course, because of the expanding atmospheric sponge.”
Follow-up work found that climate change has probably already increased the likelihood of an event like this in the past decade, even though there have been periods of extreme drought and wildfire.
“There are some reasons why natural climate variations might have opposed the climate change influence over this period. So we should not be too surprised if there’s a decade or two in the near future where things swing the other way, where natural climate variability pushes us back towards somewhat increased flood risk, which will be superimposed on top of the climate change risk that has accumulated quietly in the background.”
He acknowledged that in any given year, the likelihood is still low. “But even if a rare event is now half as rare as it used to be, that still makes a pretty darn big difference from an actuarial and risk assessment perspective.”
Dr. Swain reminded that in California, the amount of precipitation has not declined dramatically, but the usual amounts of rain and snow don’t go as far as it used to. The worsening droughts are being driven by increasing evaporative demand.
“We’re getting more precipitation on fewer days, there’s more rain rather than snow in the mountains, and also stronger evaporative demand, the dry side of that expanding sponge. Droughts used to be hot or cold; you could get low precipitation in a warm year or low precipitation in a cool year. Now they’re pretty much just all hot because it’s hot more often than it isn’t these days.”
What drives droughts in California often differs from what drives Colorado basin droughts. “The multi-decadal, extremely severe drought, which has been termed a megadrought by some paleo climatologists, has been made about 50% more intense just by the warming, drying, and increased thirstiness of the atmosphere. That’s not a small increase, and it’s argued that it made what would have been otherwise a more moderate dry period into a megadrought. So perhaps we would not even have been a Colorado basin megadrought in the first place without that warming.”
The future: Larger, more intense wildfires; fewer but more intense floods
The dry side of the expanding atmospheric sponge is driving the observed wildfire trends. Landscape-level aridity is the primary connection between climate change and wildfire intensity and severity. As of 2018, the extreme fire weather conditions in California had already doubled – which is not a small number, Dr. Swain noted. This is mainly due to the expanding atmospheric sponge demanding more water from the landscape, from the soil, from both living and dead plants, and not necessarily delivering more water in convenient times and convenient forms, he said. In California, climate change had already more than doubled occurrence of extreme fire weather conditions between 1980-2018.
This leads to a conundrum: if extreme precipitation events are increasing, why haven’t floods increased accordingly? Dr. Swain said that the more common floods either have stayed about the same or decreased because, on average, the atmosphere is thirstier, so it’s easier to re-extract that antecedent water back out of the land surface or out of bodies of water.
But he said a different process seems to be at play for the very most extreme floods. “While runoff is potentially increasing for low to moderate precipitation events, it’s actually staying the same or increasing for the very most extreme events, which are the ones that are increasing the most, but they’re also the rarest. So we’re talking about events that might occur every 50 or 100 years in a stable climate. Since we don’t observe these events as commonly, therefore we’re basing our assumption that floods are increasing primarily off the most commonly observed events that occurred 5, 10, and 20 years ago, but not 100 years floods, which are precisely those which are probably going to increase the most.”
The physical reality is that both the intensity of precipitation and aridity is increasing. There are still the occasional big snow years, but on average, there is less snowpack over a shorter season and more extreme heat and runoff associated with it. So, our historical management paradigms are not always going to be effective.
“In an era of increasing hydroclimate whiplash, flexible and proactive interventions are needed – essentially being able to roll with the punches as they come, irregularly and with increased frequency and intensity. That’s going to have to be the way of the future.”
It also means learning to embrace a gentler version of what you’re afraid of. “From a wildfire perspective, this may mean, for example, more prescribed fire. So, more good fire, beneficial risk, reducing fire on the landscape to prevent wildfire catastrophes, much as we may have to embrace more water on the landscape during the wet and not-so-wet periods with floodplain restoration and even expansion. So letting the water do its thing to a point within some limited bounds, much like letting fire do its thing, to prevent the ones we really don’t want to see.”
There needs to be buy-in and funding for projects that focus on resilience and win-win solutions that are a good idea even without climate change. We need nimble farming practices and irrigation techniques to create flexible application of water and flexible uses of land when either water is unavailable or is scarce, as well as when it is overabundant. California has long been predisposed to droughts and floods even without climate change, and we know that much bigger events are possible just based on the paleoclimate record.
Closing thoughts …
- Climate change has arrived—no longer a prediction regarding the future, but an observed reality in the present.
- A warmer California will be wetter and drier, depending on how you measure it, what time of year you’re measuring it, and also which year you happen to be in due to increasing “hydroclimate whiplash.” Blame the “expanding atmospheric sponge!
- There will be more severe droughts & wildfires, but also more severe floods. We will likely experience both droughts & floods beyond historical experience. There will be droughts; they are getting worse, and they will continue to worsen.
- Eventually, there will be more severe floods, and the lack of a recent increase in floods doesn’t necessarily predict what the future holds in terms of extreme flood risk. There will likely be floods in California in the next three or four decades that are outside of historical experience.
- The big question: how can we effectively and equitably co-manage increasing risks of water scarcity & overabundance
- Interventions that are flexible in both time and space will be key to adapting to our new climate reality.
- There is a great need to more deeply integrate climate change—especially intensifying extremes—into planning, policy, & adaptation. If we don’t do that and focus on changes in the mean or the average, we will completely miss the extremes.
- Farmers (and irrigators of all kinds!), water management agencies, and anyone in the “business of water” generally will be on the front lines of climate change in California (and beyond).
“It has become a little bit easier to acknowledge that in recent years as we’ve seen some of these extraordinary extremes unfold, but I still think we’re working in some respects from behind the curve,” said Dr. Swain. “We’re catching up, and the climate isn’t going to wait for us. So everyone in this room, whether you necessarily thought about it that way or not, is on the front lines of a changing climate, and I think we’re getting a sense, a better sense, of exactly what that looks like in terms of increasing whiplash in a warming California.”
