The Maui Fires Reveal the Growing Danger of Compound Climate Events
Climate impacts are starting to collide.
The wildfires that devastated Maui on Wednesday were exacerbated by strong winds intensified by a hurricane hundreds of miles offshore, according to meteorologists. While the precise relationship between the fires, the hurricane, and climate change has yet to be determined, these kinds of “compound” events are likely to increase in a warming world, with consequences that are hard to predict.
Hurricane Dora, which formed in the Pacific last week, did not cause the fires, nor did it directly “fan the flames.” The hurricane had become a Category 4 storm by Tuesday night when the fires in Maui ignited, but the storm remained hundreds of miles offshore and its associated rain and wind never reached the island.
As Ginger Zee, chief meteorologist and managing editor of the climate unit at ABC News, explains it, when the hurricane’s low-pressure system ground up against a high-pressure weather system just north of Hawaii, it created a force that amplified existing downslope tradewinds to 40 to 60 miles per hour.
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While the initial cause of the fires is still unknown, the unusually strong, dry winds helped them spread quickly. “It is fair to say that, at least indirectly, these hurricanes south of Hawaii may have contributed to what will probably be the worst wildfire disaster, and potentially one of the worst disasters, period, in the history of the state of Hawaii,” said the University of California, Los Angeles, climate scientist Daniel Swain during a livestream on Youtube Wednesday night.
There are many other factors that contributed to the severity of the fires, including a drought that turned non-native grasses into a tinderbox and the expansion of the urban footprint into fire-prone areas. Swain noted that this wasn’t even that large of a fire in the scheme of things; it just occurred in a highly populated area.
But this isn’t the first time that a hurricane has exacerbated fire conditions in the Aloha State. In August 2018, Hurricanes Hector and Lane brought high winds directly to the islands that fanned a series of major wildfires — some of the largest on record — according to the Pacific Fire Exchange, a wildfire science research group based in Hawaii.
In both 2018 and this week, the confluence of events made emergency response challenging. Helicopters that could have been deployed to put out the fires were grounded due to the winds. The wind also knocked out the power to 13,000 households in Maui on Tuesday night, complicating evacuations.
Scientists call this a “compound event,” when multiple weather or climate-driven factors come together, causing more dangerous disasters than they would individually. The most common example is a drought co-occurring with a heatwave, which can exacerbate fire risk, threaten agriculture, and make water scarce. Hurricanes, by themselves, are another form of compound event, as they can produce both wind-driven impacts like coastal storm surge as well as precipitation-driven flooding.
“Compound event research has blossomed in recent years,” Flavio Lehner, an atmospheric scientist at Cornell University, told me, “because we recognize that some of the most impactful extreme events are because of certain factors coming together at the right time, or at the wrong time.”
Lehner said it’s extremely challenging to predict what’s going to happen in the future with compound events because there’s basically double the uncertainty. Take droughts and heatwaves, for example. Different climate models might disagree about how much warmer it’s going to get in the future and how much it will rain. So it’s very hard to draw conclusions about how much more frequent or severe the chance of simultaneous high temperatures and low rainfall will be in any given region.
That being said, scientists do know the direction these events are trending in. Hurricanes will drop more rain and their winds are likely to intensify. Drought conditions will increase.
“Some of these extreme events, they just bring to the forefront vulnerabilities that have existed that might have been exposed even without climate change,” said Lehner. “So confronting our infrastructure or our plans to adapt in case of an emergency, that's really what I think we have to take away from these kinds of events.”
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