It was the perfect storm of fuel, heat and oxygen — the three elements that spark a fire.

The fuel, in the form of hundreds of acres of dry brush at the height of Hawaii’s hot summer, paired with ramped-up winds as Hurricane Dora passed south of the isles resulted in a deadly combination. Once ignited, Maui’s fires spread swiftly.

While some say these fires came as a surprise, scientists have warned of these potential risks.

In a study following Hurricane Lane in 2018, scientists from the University of Hawaii at Manoa and East-West Center noted that despite never making landfall, the storm resulted not only in severe flooding, but multiple fires on the islands of Maui and Oahu.

“There are so many similarities between this event and that one,” said Alison Nugent, an associate professor in atmospheric sciences at UH-Manoa. “Mainly, I think the thing that’s not surprising to me at all was the fact that both times, fires occurred on the leeward sides of the islands.”

During Lane, three wildfires broke out on Maui, including one near Lahaina, and one by the Kahe Point power plant on Oahu.

Hurricane Lane, they said, was a textbook example of compounding hazards that can be produced by a single storm.

While heavy rain is a familiar feature of tropical storms, subsiding air around the storm’s periphery is warm and dry — and combined with intense winds — increases the fire hazard. Lane brought winds to dry lands.

More importantly, the fires ignited in land dominated by nonnative grasses that replaced what used to be pineapple plantations and sugar cane fields, according to Nugent, one of six authors of “Fire and Rain: The Legacy of Hurricane Lane in Hawaii,” published in 2020.

There was also a very wet season prior to the onslaught of drought that increased vegetation to “prime the fuel,” she said. Add in the mountain effect, or the acceleration of downslope winds, and that’s a recipe for a rapid-spreading fire.

What’s unique to Hawaii, Nugent said, is that hurricane season coincides with the dry season, increasing the potential for fires.

With a death toll of at least 96, thousands of structures destroyed and the town of Lahaina obliterated, the Maui wildfires are considered Hawaii’s deadliest natural disaster since statehood.

“I’m certainly shocked in terms of the severity,” she said, “to see a place that’s so beloved and so beautiful, with so much history, to just be wiped off the map in one night. That’s shocking, and there’s no word for it.”

Fuel for fires

Clay Trauernicht, an ecosystem fire specialist at UH-Manoa, has for years warned of the growing acreage of invasive, fire-prone grasses and brush that provide fuel for wildfires.

The list includes guinea grass, fountain grass and the ubiquitous haole koa that have overtaken abandoned agricultural lands.

The haole koa is notorious for seed pods that lift into the air, he said, allowing fires to jump across rows. The invasive grasses usually grow in savannas where native grazers keep them down, but in Hawaii, they have quickly taken over.

“We’re off the charts when we talk about the quantity, especially guinea grass, which is one of the prime suspects around Lahaina,” Trauernicht said.

These vast tracts of nonnative grasses on unmanaged lands make Hawaii particularly vulnerable to fires.

“We’ve had glimpses of this,” he said, citing West Maui fires in 2018 that resulted in the loss of 21 homes followed by more brush fires in 2019. “We’ve had glimpses of fires burning like this on Maui, Oahu — pretty much all islands have had fires at this scale.”

Wildfires are now burning through four times more acres in Hawaii than in previous decades, according to Trauernicht — 20,000 acres versus 5,000 acres, on average.

“We’ve seen a 300% increase in annual area burns,” he said. “That, I’m confident to attribute to the decline in agricultural production and the proliferation of these grasslands.”

Most of these fires, so far, have threatened mostly watershed forests and wildlands, without damage to homes and structures. It’s a testament to how well firefighters have done their jobs, he said.

The best line of defense are management projects to mitigate these fuels and their connectivity. This includes the creation of mowed “fuel breaks,” targeted grazing by animals such as goats, cattle and sheep, and the restoration of Hawaiian loi, or taro patches less vulnerable to fires.

They need to be done at large scale, with coordination across various land ownerships and boundaries. But they need to be done well before a red flag warning, not during one.

“Even with the best forecasting, it’s not enough time to do the work that needs to be done to prevent those fires,” he said. “Management is months ahead, years ahead.”

Lahaina at risk

The question on many minds includes whether the fires were predictable.

The National Weather Service had issued a red flag warning for increased fire danger for leeward areas several days prior to the flames that broke out Tuesday in Upcountry Maui and Lahaina.

There were multiple weather alerts, including high-wind, high-surf and high-gale warnings as Hurricane Dora traveled past.

Based on a weather service summary, peak winds reached up to 82 mph in Hawaii County, where firefighters also battled fires in North and South Kohala. Peak winds were measured at 67 mph in Kula, Maui. No records were available for Lahaina.

Winds that strong are unusual for the summertime, according to weather service meteorologist Genki Kino, when trades usually range from 15 to 25 mph. The relative humidity in Kula on Tuesday also dropped to an unusual low of 11%.

Elizabeth Pickett, co- executive director of the Hawaii Wildfire Management Organization, has worked for years to raise awareness about the state’s wildfire problem.

Lahaina is considered extremely vulnerable to wildfire risks, she said, due to its topography and proximity to grasses.

It’s all detailed in the Western Maui Community Wildfire Protection Plan from 2014, complete with hazards assessments, maps and recommended actions.

Lahaina town, with its low rainfall, dense population and position downslope of fallow agricultural lands and the West Maui Mountains, was rated a high fire environment hazard, while mauka areas were rated as extreme.

The nonprofit has published wildfire protection plans for communities statewide, including Upcountry Maui, West Oahu and North Hawaii.

The plans also look at issues such evacuation, communications and alert notifications. Among its recommendations for Western Maui was a second egress road in case of road closures.

Climate change

Many point to climate change as a factor in the increasing frequency of natural disasters worldwide — from record-high temperatures to floods and weather events that swing from one extreme to another.

A pivot from a wet and rainy winter to sudden dryness, as happened this year, results in more fuel for fires.

“It’s like a one-two punch,” Trauernicht said, “and I have papers where we show heavy rainfalls in the year prior to a fire incident can contribute more so than drought during the fire. That’s because of this big fuel buildup.”

Hawaii also has some of the highest recorded number of fires per square kilometer per year, the study noted, caused primarily by human activity.

Pickett said Hawaii’s ecology has changed over the decades into a fire-prone state because of the proliferation of invasive species, along with increases in drought episodes.

That’s expected to continue. The NOAA Climate Prediction Center has warned of lower rainfall, with worsening drought conditions to persist in the next few months.

The authors of “Fire and Rain,” including Trauernicht, noted hurricane risk in Hawaii and the Pacific region in general is expected to increase as a warming climate fuels stronger storms and rains.

Hurricane Lane brought the risk of compounding hazards to light, they said, which is worth examining as they are likely to increase with a changing climate.

Even as someone who studies fires and knows the risks, Trauernicht was horrified by images of Lahaina’s destruction.

“We were fearful,” he said. “We knew the potential for bigger impacts. We knew it was there. I don’t think anyone would have imagined it would have been this horrific.”