Australia is under a fiery siege. Bush fires have leaped over rivers, merged with other fires and spawned fire-generated thunderstorms. It is one of the continent’s worst bush fire episodes on record.

As fires have surged into vulnerable zones, officials have urged tourists and residents to evacuate. The blazes, intensified by climate change, have in some cases spread so quickly that fleeing the fires is no longer feasible.

The situation has become so desperate that officials are offering messages of last resort: Shelter in place and prepare for the fire.

This scenario presented itself last weekend in eastern Victoria. As fires erupted amid record-breaking temperatures, notices to “Evacuate now” went out to many rural towns while there was still time and a clear route out. But by afternoon, fires were on the move, and because roads had been affected by smoke or flames, a steady stream of emergency warnings for fast-spreading blazes announced that it was “too late to leave.”

Bush fire messaging then turned toward helping people endure the passage of a fire front, and that may become increasingly necessary in a warming world.

Deadly fires in Australia, as well as in California and Europe, have been too explosive and unpredictable for everyone to escape.

“Climate change is producing more frequently these unprecedented conditions,” said Crystal Kolden, a professor and fire scientist at the University of Idaho. “Fires are moving faster than people have ever seen.”

Too late to leave

Leaving before a bush fire threatens is always the safest option, but it’s not always possible.

“Historically, late evacuation has been a major cause of bush fire fatalities,” Joshua Whittaker, a research fellow at the University of Wollongong’s Center for Environmental Risk Management of Bushfires, said in an email. “As such, Australian fire services try to discourage people from leaving at the last minute, when they are more likely to encounter hazards such as flames, fallen trees, thick smoke and road accidents.”

The dangers of fleeing during a wildfire are well-established and can account for a large proportion of fire disaster fatalities.

“We see this everywhere globally,” Kolden said.

Vivid examples include the June 2017 Portugal firestorms and the July 2018 fires in Greece. Many also died in last-minute attempts to outrun the 2003 Cedar Fire, the 2017 Tubbs Fire and the 2018 Camp Fire in California.

For those in the fire front’s path, the greatest danger lies in exposure to intense heat and smoke — a bush fire’s two biggest killers. Australia’s warning messages direct people to immediately seek shelter in a solid structure and to wear sturdy shoes and protective clothing made of natural fibers that won’t melt, such as cotton or wool. As fires spread across East Gippsland, Victoria, over the past week, some messages were particularly urgent and graphic:

You must take shelter before the fire arrives. The extreme heat is likely to kill you well before the flames reach you.

Active sheltering

Although leaving late can be deadly, more than half of the 173 people who died during Victoria’s extreme Black Saturday fires of Feb. 7, 2009, were actually found in homes, which was a sharp departure from fatality patterns in previous bush fire disasters.

Kolden called Black Saturday a “real reckoning” because the fires moved faster than anyone had anticipated.

With more than 400 blazes spreading quickly during high winds and soaring temperatures, those who were trapped were forced to improvise.

“Many people were unaware they were at risk and did not receive warnings in time to safely evacuate,” Whittaker said. “Many of those who died were not prepared to shelter and did not know how to do so safely.”

There was scant research on safe sheltering practices because Australia’s established bush-fire policy, known as “Prepare, Stay and Defend or Leave Early,” offered two choices: 1. Leave well before a fire arrives or 2. Stay and defend your home — a long, arduous process that is only for the most prepared homes and homeowners. As bush fires raced across the landscape in February 2009, people needed alternatives, and often more than one place of refuge.

Recent research by Whittaker and others, along with investigations into the Black Saturday disaster, has informed guidelines for sheltering when it’s too late to leave. Although “shelter in place” implies simply waiting indoors for the fire to pass, experts have found that surviving a bush fire requires constant monitoring and activity.

They recommend a practice called active sheltering, which may include extinguishing fires both inside and around the house, monitoring the fire’s location or leaving a burning house to seek refuge in a nearby location, like an already burned-out field. It’s also important to shelter in a room with two exits and with a clear view of the outside, ideally on the side of the house farthest from the fire.

On Black Saturday, 57 people sought protection in a bathroom — now considered the worst room to shelter from a bush fire — and of those, 37 became trapped and perished.

These recommendations for active sheltering are now integrated into bush-fire warning messages across Australia, many of which have been broadcast repeatedly during this year’s fire season:

In the United States, wildfires that threaten communities are handled through evacuations directed by local law enforcement. “Australia has long had this concept of shelter-in-place, and we simply don’t do it in the U.S.,” Kolden said. There are, however, a few communities planning for shelter-in-place scenarios, such as Rancho Santa Fe, Calif., near San Diego.

Refuges of last resort

Given the high number of fatalities in the 2009 Victorian bush fires, a commission undertook a thorough investigation and issued a final report less than 18 months after the disaster. One of the commission’s most important findings, according to Whittaker, was the need for officially designated shelters for those who cannot evacuate or defend homes. States now recognize that certain locations, like athletic fields or community centers, could provide protection during a bush fire.

Emergency warnings in the past week directed people to these areas, and also suggested open fields, beaches, bodies of water and other areas as possible places of refuge.

In Mallacoota in southeastern Victoria, 4,000 people sought protection on a beach as fire encroached and smoke enveloped the town, while others sheltered in a community center.

With a long summer remaining and many communities still under threat, Whittaker said, it’s too early to say what key lessons will emerge from Australia’s catastrophic 2019-20 fire season.

“But given the scale, severity and impact of the fires to date, there will undoubtedly be a major public inquiry,” he said. “Public debate has already turned to the role of climate change in these fires and important questions are being asked about our capacity to manage fire in a changing climate.”

Kolden said recent fires in California, Australia and elsewhere are exhibiting “extreme conditions that are unprecedented and that there’s no memory for.”

That means lessons from the past might not be enough to guard against future disasters, and it might require planning for fire scenarios that have no historical analogue.