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A hot, dry, windy spring has sparked new wildfires across the Southwest and the Great Plains, which have burned more than 150,000 acres and led to emergency declarations in Arizona and New Mexico.

The fires are part of a longer-term pattern across the US, as increasingly variable conditions have made fast-growing fires possible any time of year, rather than in discrete “fire seasons.”

A blaze in northern Arizona called the Tunnel Fire began on scrubby grassland 14 miles northeast of Flagstaff. It shot east through the dry understory, and has scorched pine and juniper forest. Around 750 households were forced to evacuate, and 30 homes so far have burned.

The fire spread over a highway and surrounding suburb north of Flagstaff, before climbing into mountains further northeast. As of Monday, April 25, the fire was just a few miles away from the Navajo Nation reservation’s southwestern edge, and on Friday, the Arizona Republic reported that the nation was assisting 20 families who had evacuated.

As of Sunday, Arizona had lifted the evacuation order for the Tunnel Fire and reopened the highway. The federal fire agency managing the response warned residents to stay on alert for renewed evacuations, and be aware of hazards caused by smoldering fires or weakened trees. Fire crews are now working to dig firebreaks, open clearings to slow down fire spread, along the eastern edge during a break in the wind.

Around the same time in New Mexico, a pair of fires on the eastern slope of the Rockies have covered more than 100,000 acres. On Saturday, the state’s governor, Michelle Lujan Grisham, said that hundreds of buildings were destroyed, and that winds had gusted up to 90 miles per hour. There too, dry pine forest and shrubby oak trees were burning quickly on steep slopes, making firefighting dangerous.

The intense winds that have spread the fires have also made them difficult to fight. Carl Schwope, the incident commander for the Calf Canyon Fire in New Mexico, told the Santa Fe New Mexican that the wind was so fierce that blowing smoke made it hard to distinguish where the fires were.

The intense wind died down by the beginning of this week, and a cold front brought rain to the New Mexico mountains, according to the federal emergency response database InciWeb. That’s given fire crews a respite to dig out firebreaks between the blaze and the town of Mora, which is under an evacuation order. But by midweek, weather forecasts on InciWeb predict that winds will pick back up, and possibly change direction.

“April is a little early for large fires in the Southwest,” says Stephen Pyne, a fire historian at Arizona State University. But a dry winter and spring have set up a year “when strong winds associated with passing cold fronts drive large fires.”

Spring fires, which are fueled by dead grasses and shrubs from the previous winter, tend to burn in the time between snowmelt and green-up.

Those conditions are partly due to the region’s 20-year megadrought, the worst dry spell since 800 AD, which has been magnified by climate change. But “fire is a combination of things,” says Andreas Prein, who models extreme weather events at the National Center for Atmospheric Research. The fast-moving fires across the Southwest also require high winds.

[Related: The American West is drier than it’s been in at least 1,200 years]

Prein says that he now receives fire evacuation warnings almost weekly at his home in Boulder, Colorado. “Every time there’s wind, there’s high fire danger,” he says. And windy fire is also hard to fight. It grounds aircraft, and can burn over firefighters, so agencies may have no choice but to fall back.

The causes of the recent fires are still under investigation, but Pyne says that lightning isn’t likely a source of ignition in Arizona until the midsummer monsoons. So that means that people probably started the fire. Although this can happen by accident—a dragging chain that creates sparks on the road, a prescribed fire that jumps out of control, a windstorm that takes out a powerline—Pyne says that “careless[ness] is more common than unlucky.”

“Of course, if you double your population, like we saw in many of these places,” says Prein, it’s more likely that a human ignition will line up with a bad drought and a windstorm.

While dry, windy days have also fueled a hyperactive fire season on the Great Plains, they’re probably not directly related to the conditions in the Southwest. As Prein points out, the plains often receive rain from the Gulf of Mexico, rather than the Pacific where the Southwest gets its moisture. “Climate change is increasing the risk generally across multiple regions,” he says, making it more likely that fire conditions will emerge independently.

[Related: What’s behind the unusual wildfires burning through Texas]

“From a fire and drought perspective, until summer we are in bad conditions,” says Prein. “Then it’s the question of how the next monsoon season will turn out. It looks fairly dry.”

The Southwest’s fires are just the latest flare-up in an already active winter and spring fire season. Fires have burned across central Texas, Kansas, and the plains east of Boulder. Since late last week, a grass fire has raced across southern Nebraska, moving 28 miles north in the span of a few days. According to information posted on InciWeb, the fire has moved exceptionally quickly, torching shrubs and trees, and jumping forward on spreading embers. Over the weekend, the fire killed an ex-fire chief, and injured 15 other firefighters.

Climate change is still likely a central factor. A 2019 study found that the grasslands of the Great Plains, as well as the eastern slope of the Rockies, will be at particular risk for spring fires because they stand to see increases in the triple threat of drought, dry soils, and late-spring frosts, which can create more dead fuel.

However, these destructive fires can be tamed if the preventative steps are taken, the study authors noted. Land managers could use prescribed fire to reduce fuel loads and set the stage for less intense fires, or manage wetlands that would act as firebreaks. This spring’s fire conditions will likely become normal going forward, Prein says. Without huge investments in fire mitigation, the risk to communities will be too.

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