Why holdover, or 'zombie,' wildfires are a bigger problem for B.C. this year

In Fort Nelson, all eyes are on the Parker Creek wildfire, which on May 10, prompted the evacuation of more than 4,700 people in B.C.'s far northeast after a tree blew down on a power line, pushing flames toward the community.

But crews are also watching one of the largest wildfires burning in Western Canada — the Patry Creek fire, 25 kilometres north of Fort Nelson, B.C. — which re-emerged May 2 after smouldering through the winter and measures more than 700 square kilometres.

Patry Creek is a so-called holdover fire, and wildfire officials in British Columbia have expressed concern that last year's record fire season, along with continued drought conditions, will mean more such fires remain a threat. 

The Nogah Creek wildfire, east of the community, is also a holdover fire that burning at more than 835 square kilometres. 

In fact, people in the Fort Nelson region started reporting and recording wildfire smoke as early as December 2023, while there was still snow on the ground and the B.C. Wildfire Service put out an early warning that with dry conditions, these holdover fires could pose a bigger threat than in years past.

WATCH | Wildfire smoke near Fort Nelson in December 2023: 

Wildfire smoke still smouldering near Fort Nelson, B.C.

9 months ago

Duration 1:36

An unusually dry winter had led to more than 100 wildfires still burning underground across Canada. That's particularly concerning in Fort Nelson, in B.C.'s far northeast, where smoke is still visible near the community

Here's a closer look at what holdover fires are and their threat to Western Canada.

What are holdover fires?

The B.C. Wildfire Service defines a holdover as "a fire that remains dormant and undetected for a considerable time after it starts."

They are also sometimes called "overwintering" or "zombie" fires due to the fact they seemingly come back from the dead.

The service said in a blog post in February that such situations are especially common with lightning-caused fires, large-scale wildfires or those happening with dry fuels seven centimetres or deeper underground.

When the conditions are right, fires burning deep underground can "slumber" undetected, simmering even under snow for possibly months after ignition.

These fires can then emerge when the weather warms and dries in the spring, as was the case with Patry Creek, which overlaps with a wildfire area that initially ignited by lightning in July 2023.

Is this a new phenomenon?

"It's certainly something that, as an agency, we have dealt with holdover fires for my entire career for 21 years," B.C. Wildfire Service director of operations Cliff Chapman told the Canadian Press. "This is not a new situation for British Columbia."

Chapman said firefighters in Alberta and Manitoba have also seen holdover fires this year.

What has changed, Chapman said, was the more than 28,000 square kilometres of land that burned in B.C. last year, which when combined with drought conditions has "amplified" the risk stemming from such wildfires.

Holdover fires part of wildfire threat in B.C.’s northeast

7 months ago

Duration 1:55

As wildfire threatens Fort Nelson, B.C., from the west, there are also much larger fires burning to the east of the town. They're known as holdover fires — ones that never completely went out last year. Chad Pawson has more on those fires.

In January, more than 100 wildfires were still listed as burning in B.C., a number much higher than the typical few dozen holdovers from year to year, according to B.C. Wildfire Service spokesman Forrest Tower.

The B.C. River Forecast Centre says persistent drought conditions in B.C. stretch back to 2022 and the province is heading into this summer with "multi-year" precipitation deficits, with the average snowpack level lower than ever recorded.

Why can't these fires be put out during the winter?

Chapman said the wildfire service does plan for holdovers, and concern of their emergence this spring was one reason why teams were already in Fort Nelson before attention was turned to the Parker Lake fire, which now threatens the community and forced 4,700 people from their homes. 

Detection of holdover fires is a major challenge because of how deep they can burn, Chapman said.

"It is important to note that just because the fires were underground, there was still snow on top of these fires," he said. "They were not producing heat signatures for a big portion of the winter.

"We had very limited heat signatures until it started to become snow-free."

Lori Daniels, a forest ecology professor at University of British Columbia in Vancouver, said some of last year's fires had perimeters that were "very large and convoluted," making tracking them over the winter difficult.

"We expect that there's going to be places along that perimeter that we just couldn't get to and ensure the fire was out at the end of fire season," she said.

Tower told the Canadian Press that the depth of the holdover fires presents another challenge, even when they are found.

"It's just how deep some of these fires burned and the size of them," he said in January. "It takes a ton of manual labour to dig deep enough or to access some of these more remote fires."

Are other parts of B.C. at risk?

At a Friday afternoon news conference, Chapman was asked if there were worries other parts of B.C. could be at risk of holdover fires.

He said while it's always a possibility, the primary concern is in the Prince George Fire Zone, which covers the entirety of northeastern B.C., including Fort Nelson and, to a lesser extent, the Cariboo and Kamloops fire centres.

These are the regions, he said, where large fires burned last year, putting them at greatest risk of having holdover fires return.

The Fort Nelson region, he said, was particularly vulnerable due to the vegetation and dry conditions in the area.

"It's really that bog-type fuel where fire can really hold underground," he said.

What lessons can be learned?

Chapman told the Canadian Press that Fort Nelson wildfire experience is likely something the wildfire service will learn from in terms of anticipating the impact of future holdover fires.

He said the wildfire service will continue to work with land-users and other levels of government to understand where fires are simmering from year to year, in order to deal with future recurrences.

But the key may be to stop as many fires as possible from being started in the first place, Chapman said.

"The answer to a lot of these questions is really in prevention," he said. "It's really in FireSmart, it's really in using the B.C. Wildfire Service initiatives, the ministry initiatives, trying to create a more resilient land base, which is a much broader question."