Towering nearly 6,000 feet, the West Maui Mountains are a dramatic, defining feature of the Hawaiian island—verdant peaks surrounded by sparkling blue waters. But on August 8, they became deadly, helping to unleash hell on the town of Lahaina. Wind poured down the mountains like an avalanche, accelerating to 60-mile-per-hour gusts that got drier and drier as they descended. The winds sucked away the remaining moisture in already parched vegetation, turning the landscape into tinder. Then all it took was a spark.
“When you get 60-mile-an-hour winds, the fact is you’re not going to stop any fire, period,” says Jack Minassian, the Fire Science program coordinator at Hawaii Community College. “The only thing that stopped that fire was when it reached the ocean and ran out of fuel. The only thing you do when you have 60-mile-an-hour winds is just get people out of the way.”
Many people couldn’t: The death toll stands at 115, with 850 still reported missing. The worst-case fire scenario that’s played out across the continental United States over recent years—the Camp Fire that destroyed the town of Paradise, killing 85, and the Tubbs Fire that tore through Santa Rosa, killing 22—is now tropical Hawaii’s problem as well. While there is no single reason why wildfires have gotten so bad, a common denominator is wind. And of all the drivers of wildfires, it’s the thing we can’t do anything about.
Long before the winds gusted on August 8, invasive grasses had primed Maui’s landscape to burn. European colonizers brought these with them, when they established plantations on the Hawaiian islands. Those grasses have since spread out of control, covering a quarter of the state—growing across abandoned plantations, along roadsides, between houses. They grow rapidly during the rainy season, and wither quickly during the dry season, which is ongoing right now on Maui. The island is also deep in a drought.
Climate change is helping supercharge these sorts of wind-driven fires. Generally speaking, the hotter the atmosphere gets, the more moisture it can hold, and the more moisture it can remove from vegetation that acts as a fire’s fuel. Scientists are still working to figure out exactly how much climate change contributed to the blaze that destroyed Lahaina, but it’s clear that it is a factor: On a warmer planet, droughts become more common and more intense. Between the years 1920 and 2012, over 90 percent of Hawaii saw a drying trend.
So the grass around Lahaina was ready to burn, and in a matter of hours, those dry winds evaporated what little moisture remained. Think of it like letting your hair air-dry for a while, then blasting it with a hair dryer. The same dynamic is also at play in California’s increasingly catastrophic wildfires: An already-dry landscape can be scoured by winds racing down the Sierra Nevada mountains.
Winds blowing at 60 miles an hour not only push the flames along, they also help start new fires. Wildland firefighters on the US mainland regularly struggle with embers blowing miles ahead of the main blaze, starting new ones downwind. The same likely happened across the town of Lahaina, making it impossible to stamp out all the new fires. “That’s probably how most of the fires started, from embers accumulating,” says Minassian. “You can see it in some of the pictures there—they show embers all over the place.”
It is exceedingly difficult to predict where winds might drive a fire, because wind is an exceedingly complex phenomenon. It interacts with the landscape in granular ways: It moves differently over grasslands than it does through wooded areas, where it flows between trees. “How is the wind channelized in the gap between two trees? Believe it or not, that actually matters a lot,” says UC Irvine atmospheric scientist Tirtha Banerjee, who studies how wind influences wildfire. “That has an impact on how the fire burns.” And once those winds reached the town of Lahaina, they poured between buildings in complicated ways, further confounding predictions for where the fire might spread.
Climate change is clearly worsening wildfires due to hotter temperatures and gnarlier droughts, and scientists are now trying to work out how it might tweak the way winds flow. “There’s a lot more uncertainty because wind is so local, and the small-scale variations on the land surface can really change the patterns,” says Banerjee. “Mountainous terrain can create this little local recirculation that can actually make your fires more unpredictable.”
Indeed, fire behavior—the dynamics of how wildfire spreads across the landscape—is getting increasingly chaotic due to the combination of climate change, accumulated fuels, and wind. That’s making wildfires increasingly difficult to fight. “We’ve been seeing a lot of really strong, erratic winds that can just make these fires go from something manageable to something that completely levels a town,” says Kaitlyn Trudeau, a senior research associate of climate science at Climate Central, who studies wildfires. “It’s been really deadly for a lot of firefighters, who have actually gotten encircled by fire because the winds are just blowing in a way that causes a fire to burn around them into a circle.”
Part of the problem is that as supercharged wildfires get bigger and more intense, they start to create their own wind. Fire produces columns of hot air that rise into the atmosphere—sometimes so much of it that smoke thunderclouds form, creating lightning that sparks more fires. As that hot air ascends, air from surrounding areas rushes in to fill the void, creating additional wind. “It’s not like the fire is only responding to the winds, but the fire itself—because of the heat—actually changes the winds,” says climate scientist Ruby Leung, of the Pacific Northwest National Laboratory. “All of this can be very complicated if you want to predict where the winds are blowing.”
There’s simply no controlling the wind—but there are ways to tackle the other drivers of wildfires. In the big picture, humanity needs to dramatically reduce carbon emissions to slow climate change. And in the near term, people need to get better at managing overgrown and dead vegetation, like with controlled burns, so wildfires won’t have the fuel they need to burn out of control. You might have 60-mile-per-hour winds, and you might get a spark from downed electrical lines, but there won’t be enough tinder for a fire to turn into a city-obliterating conflagration.
“We’re seeing fire seasons getting longer, and we’re seeing fire behavior getting more extreme,” says Minassian. “That makes it more difficult to try to suppress. And we need to start thinking about evacuation plans, defensible space, things that communities and homeowners can do to minimize the threat of wildland fire.”
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