Climate change is making wildfire and hurricane seasons longer


Climate change is extending natural disaster seasons from wildfires to tornadoes to hurricanes

Just after 11 a.m. on Dec. 30, sheriff’s deputies and fire crews headed out to investigate reports of a blaze near Boulder, Colorado. Six hours later, after 100-mile-per-hour winds hurtling down off the Rockies fanned the flames across dry grasses and suburban enclaves, more than 1,000 homes in the towns of Louisville and Superior were reduced to ash.

It was among the most destructive fires in the state’s history, and it occurred about as far outside what is generally considered “wildfire season” as possible.

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In much of the American West, fire is considered a summer problem, when hot temperatures and dry forests combine to offer up perfect conditions for wildfires to spread. As the climate has changed, those warm and dry months have expanded into the “shoulder seasons” of spring and fall. The chances of anomalous major fires springing up in December and January have also increased.


And it isn’t just fires: The changing climate is rewriting the entire concept of disaster seasons, from wildfire to tornadoes to hurricanes, and forcing the nation to reassess its relationship with risk.

Policymakers and the public are understandably struggling to keep up. Resources from money to personnel that tend to be allocated on a seasonal basis may need to be made available year-round. People in vulnerable locations need to stay vigilant and plan for the worst on an expanded scale.

“There’s a huge amount of education that needs to happen,” said Crystal Raymond, an expert on fire and other climate change-related impacts at the University of Washington. “Just because you get the first snowfall of the fall or the winter might not mean you’re out of the woods.”

One study has found that climate change helped western U.S. fire seasons grow by 78 days, or 64 percent, since the 1970s. But even that is now wildly out of date; the study is from 2006, and nearly every year since then ranks among the top 15 hottest years on record. A more recent study found the average fire season length globally increased almost 19 percent between 1979 and 2013. Another analyzed fires in California from 2000 to 2019 and 1920 to 1999 and found the state’s fire season is starting earlier and lasting longer. The evidence is overwhelming that fire season is not what it used to be.

Several factors came together to prime Boulder’s southeast suburbs for the devastating late December fire. The previous spring had been particularly wet, spurring growth of the grasses that dominate the foothills east of the Rockies. The remarkably dry late summer and fall that followed turned all those grasses a crispy brown. Throw in an intense wind storm, with powerful gusts blowing down from the mountains, and fire was just a spark away. (That spark might have come from a Christian sect known as Twelve Tribes, not climate change, but climate change set the stage.)


“The drought, the long-term dryness — that climate setup enables it to happen,” Raymond said. In early December, the National Drought Monitor reported that almost 55 percent of the country was in either severe or extreme drought conditions. The new normal is a tinderbox.

Beyond fires

But climate change isn’t just raising the risk of wildfires. Only a few weeks before the Boulder disaster, an outbreak of severe storms in the Midwest spawned several long-track tornadoes. One of them tore through more than 160 miles mostly in Kentucky, causing widespread damage; all told, the storms killed at least 76 people. And just like the Boulder blaze, the tornadoes appeared well outside their traditional season, generally considered to peak from April through June.

It’s important to note that the climate change-tornado connection isn’t remotely as solid as that for fires or heat waves or some other disasters. But that doesn’t mean the connection isn’t there.

“We expect there to be an earlier season — March being a lot more active than in the future compared to historical time periods,” said Stephen Strader, an assistant professor who studies severe weather and tornadoes at Villanova University. “And we expect it to go later.”

While out-of-season tornadoes have certainly happened before, the warming climate does seem to be setting up the winter months for more of this mayhem than what was once typical in the U.S. This past December set a number of records for tornadoes, with the preliminary count of 202 twisters recorded far exceeding any previous December; it was also the 10th-deadliest month for tornadoes in the modern record, which dates to 1950. Research suggests we are priming the atmosphere to unleash that particular brand of disaster more frequently in the theoretical offseason.

And then there’s hurricanes. The only natural disaster that has an official, government-defined season is straining at those bounds thanks to climate change. Atlantic hurricane season stretches from June 1 to Nov. 30, and while there have been outlier storms in the past, they seem to be increasing in frequency. According to data from the National Oceanic and Atmospheric Administration, no decade has had as many storms form in May than the 2010s, with six. There have already been three in the first two years of the 2020s.

As with tornadoes, some of that increase may be due to better technology used to spot the storms. The modern satellite fleet and other tools can see relatively small or short-lived tropical cyclones that might have gone unnoticed before. “Even if you exclude, basically, weak crap that’s lasting less than 48 hours, you still see this increasing, you still see a shift earlier in the season,” said Phil Klotzbach, a meteorologist at Colorado State University who contributes to hurricane season forecasts.

The basic mechanism is fairly simple: The ocean’s surface has warmed substantially over the past century — and especially over the past few decades. That means the conditions required for tropical cyclones to form exist for more of the year. Because hurricane season does have official start and end dates, this is the first of these shifting periods that may provoke an obvious policy response: a change to those dates.

In fact, NOAA said in early 2021 that it had begun discussions on whether to shift the start of hurricane season to May 15, reflecting the likelihood of earlier storms. A spokesperson told Grid that those discussions, involving experts from the agency’s National Hurricane Center and National Weather Service, are ongoing, but that no such change will kick in for the 2022 season. NOAA did start issuing its Atlantic Tropical Weather Outlooks on May 15 last year, even without the official date change.

A shift like that is not just about the science and frequency of storms. The consideration, according to the NOAA spokesperson, will include “a detailed social science study” of the potential impacts of redefining hurricane season. Klotzbach pointed out that just adding some more days of potential catastrophe to our mental calendars may not be such a good thing.


“People are getting messaged with everything all the time,” he said. “Watch out for this, look out for that.”

Do disaster “seasons” make sense?

With hurricanes, or with fires and tornadoes, does it actually help to extend the period of potential danger in terms of public health and awareness? Hurricane season is already six months long, and the bulk of truly damaging storms tends to cluster in August and September. How vigilant do people in vulnerable areas really need to be for much of the year?

There are other implications for the shifting disaster seasons. Klotzbach noted that some insurance policies related to hurricanes are put together in May based on forecasts of the upcoming season, meaning the industry might have to change its practices — if only by a few weeks. For other types of disasters, like fires or tornadoes, it may mean rethinking how we do things year-round.

“We really can’t stop a tornado,” Strader said. “There’s nothing really to do if you’re in the path of it except for have better homes, better building codes, better enforcement of those building codes. That’s important.”

Better building practices could also be key to limiting the damage from fires. More careful management of the wildland-urban interface — the area where forests, grasslands and other bits of nature run up against humans’ built environment — could make a big difference in how much damage a fire causes. Another issue is personnel. As it stands, many firefighting jobs are seasonal, with a six-month summer period on and the winter off.


“We need to think of our wildland firefighting people resources differently,” Raymond said. “These need to be full-time jobs.”

That shift is already underway: In 2021, the Bureau of Land Management said it was moving 428 of its crew of 3,400 firefighters from seasonal to full-time. The infrastructure bill President Joe Biden signed into law in November included $600 million specifically to support firefighting efforts — a significant chunk considering the federal government’s annual average spending on fire suppression is about $2 billion.

The fact is, though, that in some cases there may not be many actions that could limit the damage from “out-of-season” disasters. The fire in Boulder last December mixed the foibles of day-to-day human behavior with a perfect climate change-enabled circumstance to produce a destructive blaze. We can try to limit the foibles, but those circumstances are only getting more likely. “We expect warming,” Raymond said, “and warming in all seasons.”

  • Dave Levitan
    Dave Levitan

    Climate Reporter

    Dave Levitan is a climate reporter for Grid where he focuses on interconnected stories about climate and science, and politics shaping action around both.