(Bloomberg) — First came a dry spell that parched the land, then a spark, followed by some wind. Suddenly, swaths of South Carolina were consumed by voracious flames.
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More than 100 fires ignited in the state last weekend — an unusually high total even in the heart of fire season. It was the perfect combination of arid air, dry fuels and gusting winds that combined to spread the flames, said Doug Wood, a spokesman for the state’s Forestry Commission.
The South Carolina disaster is the latest high-profile example of compound weather, or two or more concurrent events that collectively yield a result worse than if each had occurred on its own. It’s a global phenomenon — and its prevalence in a warming world portends the risks ahead.
Malaysia recently struggled with devastating floods that killed at least five people, sent thousands fleeing their homes, crimped palm oil production and caused mudslides throughout the region. In January, a cascading series of weather disasters led to historic Los Angeles wildfires that killed 29.
Texas — the US epicenter of extreme weather — has been hit by a string of compound events in recent years. The great freeze in 2021 that killed at least 200 people has been tied back to a series of compound events, as has last year’s record Smokehouse Creek Fire that had its roots in a massive 2023 drought that hit the Great Plains.
As the planet heats up and weather whiplash spreads, compound weather events are poised to wreak even greater havoc: A study published last year in Nature projected climate damages could cost the global economy $38 trillion (in 2005 dollars) per year by mid-century.
Deborah Brosnan, a climate risk scientist who heads up Deborah Brosnan & Associates, said the Los Angeles fires sharply illustrate the danger of multiple weather events leading to a larger disaster. The Palisades, Eaton and other blazes hit after the state saw two winters in a row of plentiful rains that allowed abundant vegetation growth. Last year was one of California’s warmest on record, which dried out that vegetation and ushered in a flash drought across the state’s southern half. The drought spread from roughly 17% of the state in late December to nearly 32% in early January when the fires started.
“LA experienced normal fires, but compounded by prolonged drought and high temperatures — both of which are associated with climate change — the outcome was worse,” Brosnan said. (Research found climate change made Los Angeles 35% more primed to burn.)
Coming up with direct costs for cascading events can be difficult because damage is often tallied by individual storms or fires. California’s fires unleashed damage that’s projected to reach $164 billion. In comparison, the financial toll of the drought that preceded them has yet to show up in any US government assessments. The compound event didn’t end once the fires were put out, either: The region has seen heavy rains falling on burn-scarred land, resulting in mudslides.
“It’s a good example of how all these things can play together to exacerbate the hazards that we’re all facing,” said Lou Gritzo, chief science officer at industrial insurer FM. “And that was just the alignment of those kind of weather events. You can argue that had any one of those not been in place, the consequences would have been significantly reduced.”
A similar situation occurred in Australia, where drought from 2017 to 2019 was followed by the 2019-2020 Black Summer Fires that tallied insurance claims of up to $1.5 billion.
Compound events have outsized impacts and they are relatively rare, making it difficult to research them, said Doug Richardson, a weather and climate research scientist at the University of New South Wales.
“We need to develop our models to better account for these sorts of interactions between different climate hazards at a spatial resolution that allows us to consider how these hazards might interact,” and to build a larger sample to assess the frequency of potential compound events, he added.
Not all cascading weather ends in flames, though. Flooding can occur when rain saturates soil and loosens vegetation, setting the stage for subsequent showers to have a greater impact. This was part of the mechanics around the Malaysian floods, which also got an assist from extreme tides.
The states of Sabah and Sarawak saw more than 27 inches (70 centimeters) of rain in January, which left soils saturated. Yet another storm hit just as tides reached their highest levels due to the alignment of the sun, Earth and moon, said Nursalleh bin Kasim, principal assistant director of the research and technical development region at the Malaysian Meteorological Department.
One extreme event can also beget another. Drought, for example, saps the soil of moisture. With no excess water to evaporate, the sun’s energy is instead redirected to heating the air. The resulting hotter weather then makes the drought worse.
“There can be a feedback back to the atmosphere,” said Ronnie Abolafia-Rosenzweig, a project scientist at the US National Center for Atmospheric Research.
Larger climate impacts, such as sea-level rise, add to the perils as does building in exposed areas, Brosnan said. Notably, deforestation leads to greater risk of landslides while destroying mangroves and coral reefs worsens coastal flooding.
Events can also be “spatially compounding,” striking multiple regions at once, said Jakob Zscheischler, a compound event researcher at the Helmholtz Centre for Environmental Research in Germany. He pointed to the fall 2024 floods that struck multiple parts of Europe as a prime example. The flooding, fueled by record rainfall from Storm Boris, killed at least 29 people and caused widespread destruction across countries from Italy to Poland to Romania. Munich Re estimated the compound event caused around $4.3 billion in damage, roughly half of which was insured.
“Climate change has already led to an increase in the amount of rain during such events and will continue to do so,” Zscheischler said, “which puts pressure on infrastructure and transnational flood management due to multiple countries being affected at the same time.”
Brosnan warned that siloed emergency management means “we deal poorly with complex events where impacts spread widely through a system.” There are precedents for non-weather disasters, though, that could prove useful if the world is to adapt to more compound events.
Bruce Chong, director of climate and sustainability at engineering firm Arup, said Japan’s culture of earthquake preparedness is one model to turn to.
“They know there are earthquakes,” he said. “At the everyday level, they are already aware and prepared across multiple aspects, including how tasks are shared between local communities and the government. It’s become something that everyone faces together.”
–With assistance from Brian Eckhouse.
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