Boom-and-bust or should I say bloom-and-burn?

Hydroclimate volatility is increasing. Los Angeles is just the tip of the iceberg.

Wildfires can be more extreme when following extreme wet periods. Photo by Sanath Kumar on Unsplash

We've all seen it but didn't have a name for it. One year, you're being battered by massive rainfall and flooding events, the next by a prolonged drought followed by devastating wildfires.

California is a poster child for these wild swings over recent years. After a long period of drought, 2022-23 saw nine atmospheric rivers hammer the state in three weeks – record-breaking precipitation resulting in widespread flooding and landslides, with disasters declared in 40 of the state’s 58 counties.

2023-24 continued this trend for the southern part of the state. Such conditions result in a massive build up in new vegetation such as grass and brush, which, when faced with prolonged drought and heatwave conditions (as have played out through 2024 and into early 2025), can become tinder dry, fuelling the flames of devastating wildfires.

And here we are. Los Angeles is burning with devastating force. And it's just one more example of what a new paper is terming "hydroclimate whiplash" – rapid swings between intensely wet and dangerously dry weather.

We all knew extreme events were increasing in frequency and magnitude, and expected to increase with continued climate change. I've discussed extreme floods before in this newsletter, for instance. But it seems we need to consider how they link together as this is when they can be particularly devastating. It's not just the isolated floods and droughts we need to be concerned about but it’s the dangerous swings between them.

I've talked before about my concern around compounding extremes (back-to-back events that can have greater impact than standalone events), but these whiplash events are a particular form of event that tend to happen in cycles. They might include "bloom-and-burn" cycles, where vegetation is overwatered followed by overdrying or it might be landslides that occur during rainfall that follows fires, where the soil/plant-root infrastructure has been damaged, for instance. An analogy can be made to New Zealand's problem with landslides following pine plantation clearance.

The paper, led by UCLA's Daniel Swain, synthesises knowledge of hydroclimate volatility in the context of climate change, including defining a metric of hydroclimate whiplash to identify the trends of such events across the world. It’s actually not a new phenomenon, but the paper sheds new light on it, bringing together the research out there and synthesising the trends.

Swain, D. L., A. F. Prein, J. T. Abatzoglou, C. M. Albano, M. Brunner, N. S. Diffenbaugh, D. Singh, C. B. Skinner, and D. Touma. 2025. Hydroclimate volatility on a warming Earth. Nature Reviews Earth & Environment 6:35–50. https://doi.org/10.1038/s43017-024-00624-z

Similar wet-to-dry or dry-to-wet transitions have been widely documented in eastern Australia over recent years. Australia jumped from the massive Black Summer fires to a three-year period very wet La Niña weather systems.

These have caused widespread human health impacts, threats to public safety, food and water security issues, and losses of infrastructure. And the paper identifies many more examples from across the world in recent years.

For instance, torrential rains during the 2023 autumn harvest season in eastern Africa destroyed thousands of hectares of crops and displaced two million people. These events followed five consecutive years of drought, which resulted in food insecurity for over 20 million people.

From original paper: "Global hydroclimate whiplash events. Location, date and impacts of select hydroclimate whiplash events from 2016 to 2023, and the corresponding magnitude of changes in the Standardized Precipitation Evapotranspiration Index (SPEI; shading). The brown shades represent wet-to-dry events and green shades dry-to-wet events. The events do not represent a comprehensive catalogue of all whiplash events but are illustrative of the breadth and diversity of geographies subject to such rapid transitions. Societally and ecologically consequential hydroclimate whiplash events can occur in virtually all land areas globally, and their impacts can be strongly affected by the direction of change (from wet to dry or dry to wet)."

The study finds that these hydroclimate whiplash events have already increased globally by 31% to 66% since the mid-20th century, more than what climate models suggest they should have.

Even more concerning is that they are projected to increase with increasing climate change. And the frequency is projected to increase more on land than in the ocean.

But what is the key driver? Well, it’s the fact that a warmer world is just more forceful when it comes to the climate. For every degree (in Celsius) of warming, the atmosphere's ability to evaporate, absorb and release water increases by 7%. That is, there are "nonlinear increases in the water holding and water evaporating potential of the atmosphere".

“The problem is that the sponge grows exponentially, like compound interest in a bank,” the study's lead author, Daniel Swain said. “The rate of expansion increases with each fraction of a degree of warming.”

What is concerning with these events is not just the precipitation or lack thereof but the fact the atmosphere is thirstier, amplifying drought by increasing the force by which moisture is sucked out of plants and soil.

From original paper: "Projected hydroclimate whiplash trends in a warming climate. a, The frequency of global weighted-average subseasonal (up to 3 months) hydroclimate whiplash events in the CESM2-LE as a function of projected global average temperature change. The solid lines represent the median and shaded areas the 5th to 95th percentile ensemble spread. b, The projected trends in subseasonal hydroclimate whiplash in CESM2-LE at 3 °C global mean warming. c, As in a, but for interannual (up to 12 months) whiplash; note the different y-axis scale. d, As in b, but for interannual whiplash. All global mean temperature increases are calculated relative to the 1940–1980 reference period. Hydroclimate whiplash increases strongly with warming over nearly all global land areas and most global ocean areas outside of the subtropics."

The consequences are huge, and the distribution of threats is unequal. High latitudes and eastwards from northern Africa to South Asia appear particularly vulnerable to increasing hydroclimate volatility.

I've talked already about the impacts of extremes on ecosystems. But this volatility will further amplify the impacts of floods, droughts and associated wildfires, and landslides on ecosystems and people alike. Hydroclimate volatility will increase disease risk too by allowing rapid growth of populations of disease vectors such as mosquitoes.

It will threaten food security for billions of people due to crop failures, and it will threaten lives through the direct impacts of cascading extremes, such as rainfall-induced landslides that follow wildfire events.

From original paper: "Cascading hydroclimate whiplash hazards in a warming climate. The pathways through which hydrological extremes and rapid whiplash transitions between wet and dry states can lead to complex effects in the broader Earth system. The dark arrows represent cascading relationships (in which the initial event causes indirect but substantial downstream effects via an intermediate step or process), and the red vertical arrows show increases or decreases in specific impacts under anthropogenic warming. The processes labelled in blue represent effects caused by wet events alone, those labelled in yellow represent those caused by dry events alone and processes labelled in grey represent those specifically caused by rapid whiplash transitions. Together, natural variability and anthropogenic climate change contribute to meteorological extremes that can cause hydroclimate whiplash events — with subsequent cascading and wide-ranging impacts that are often distinct from wet or dry extremes occurring in isolation."

So, it seems we can't just focus on managing for increasing one-off extremes. The climate is becoming more erratic. Massive pulses of water are hugely problematic for human livelihoods, infrastructure, biodiversity, but so too are the increasingly drier periods in between. Instead, we need to co-manage these events as a system to avoid the worst consequences.

Every fraction of a degree of warming counts. So, of course, the best thing we can do is limit warming. And the best way we can do that is to rapidly and drastically phase out fossil fuels. But there are other things we can do, including prioritising sensible natural climate solutions in both forests and non-forest ecosystems.

This is scary stuff, I know. But it's important to be aware of these threats so we can manage them accordingly.

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