A burning question: How is climate change shaping wildfires in the valley?

Coastal forests have historically been difficult to burn. But as climate change dries out the region during the summers, wildfires here are expected to not only become more common but to also behave differently.

By Joti Grewal | September 26, 2022 |5:00 am

Mother Nature isn’t the only cause of wildfires, but she does dictate how they behave.

Coastal forests have historically been difficult to burn. But as climate change dries out the region during the summers, wildfires here are expected to not only become more common but to also act differently.

Wildfire season in the Fraser Valley has often been marked by skies of smoke arriving from elsewhere. But the last month has been a reminder that the valley isn’t immune to burning. Just in the last few weeks, wildfires have broken out in Chilliwack’s Promontory neighbourhood, Mission’s Stave Lake, around Chilliwack Lake, and most prominently along Highway 1 outside of Hope.

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WHAT HAPPENED IN HOPE

The Flood Falls Trail wildfire just southwest of Hope was discovered on Sept. 8. For a week, it burned out of control, eventually forcing the evacuation of several nearby properties along Highway 1 in Hunter Creek, Flood Hope, and Laidlaw.

Nature isn’t to blame for the fire. Fire officials suspect it may have been human-caused. But the environment did play a major role in how the fire behaved.

“The interesting thing about the Hope fire is it’s up on that steep hillside,” said Bob Gray, a Chilliwack-based wildland fire ecologist and fire scientist. “Those forests, because they’re on shallow soils and rocky sites, they will dry out significantly—they’re open to the sun.”

There were two things that made the Flood Falls Trail wildfire difficult to fight: wind speed and geography.

“That’s a very narrow part of the Fraser Valley through Hunter Creek there, so very, very strong winds, and then there was so much smoke and high winds that you can’t attack it from the air,” Gray said. “The other thing is because it was such an ugly fire, a steep slope, rocky, you can’t put people on the ground.”

It meant crews had to wait before they could attack.

The fire eventually grew to 545 hectares in size before firefighters managed to get it under control. That’s equivalent to roughly 1,350 American football fields.

“So it did move fast across that hillside and 500 hectares I think was the final size, which is not typical for around here,” Gray said.

COASTAL FIRES VS INTERIOR FIRES

Fires burn differently in the coastal and Interior regions.

The Interior region boasts open, dry forests like ponderosa pine, Douglas fir, and Aspen. Those tall trees dry out easily, especially in the Interior’s hot summers. Fires move through them quickly. On the ground, the Interior has lots of grasses and flammable shrubs like sagebrush. Those have lots of surface area, and not much mass, allowing them to both dry and burn extremely quickly.

The coastal landscape, on the other hand, consists of dense, closed canopy forest that is blanketed in moist moss, with damp ferns on the ground. The vegetation isn’t conducive to wildfires like the Interior, but that doesn’t mean it’s immune to the flames.

“If they dry out enough, then they will burn,” Gray said. “And what happened this year, certainly what happened in 2021 with the heat dome, we’ve dried things out significantly.”

The coastal region also burns differently than the Interior.

“These systems carry a lot of biomass so that when they do burn, they produce a lot of smoke and a lot of emissions,” Gray said.

Biomass is fuel. Coastal forests produce sizable trees. When they die that material falls to the forest floor and becomes fire fuel.

“It’s stored energy waiting for a fire.”

When those fuels catch fire, they burn very hot and for a long time. Even when the flames have passed, the material will continue to smolder and produce significant smoke, like the fire near Hope. Although now deemed under control, that fire continues to burn material and is still often visible to Hope residents and Highway 1 motorists.

Particularly hot fires also often burn up the organic duff layer, the decomposed organic material on the forest floor, which could lead to sterilized soils.

Burned soil can become hydrophobic, essentially water-repelling. The hydrophobic layer prevents water from soaking through the soil. Soil impacted by wildfire is more fragile. That means the hillside along Highway 1 near Hope has an increased risk of landslides.

“The concern I have with the fire close to Hope is it’s on a very steep hillside, it did burn hot, and once the rains start this fall, then you have a really high probability of erosion,” said Gray. “And right below that fire is the highway.”

FIRE MANAGEMENT

The landscape today doesn’t look anything like it did before it was settled by Europeans, Gray said.

“There was such a heterogeneity [variety] of different vegetation communities and patches… and that resulted in small fires.” Fire was used to encourage the growth of understory plants: raspberries and plants that produce nuts and fruit.

“Fire was the tool that enabled you to do that,” Gray said. “Forest was the enemy.”

Historically, it was a challenge for humans to survive in dense, closed forests. Fire provided food security. Burning a vast amount of landscape created plant communities that Gray says didn’t burn easily, resulting in more riparian zones.

“We had a lot of shrub fields and grass fields, we had a lot of hardwood forest that doesn’t burn very well in the summertime,” he said. “It ended up limiting fire size. Historically, you just didn’t get those 200,000 hectare fires that we see today.”

Research shows fires historically occurred in the springtime, said Gray. Fires were more frequent but less intense.

“The Indigenous people had a very sophisticated understanding of fire effects and they could burn for very specific purposes.”

Then British Columbia outlawed Indigenous fire techniques.

The Bush Fire Act of 1874 was the earliest form of legislation passed in BC to manage forest fires. Gray said banning traditional uses of fire had a significant and long-term impact on wildfires.

“It changed our fire regimes from very frequent in parts of the southern Interior—frequent that they were just such low intensity that the flame lengths were like 10 centimeters in height, most of the time,” Gray said.

“And now we have catastrophic fires: they don’t occur very frequently, but when they do occur, they’re crown fires, and they cover large areas.”

A crown fire is a blaze that leaps from the ground to a forest canopy. It can spread rapidly from treetop to treetop. It behaves the same in both the coastal and Interior regions.

Gray describes crown fires as a process of preheating. The surface fire preheats the different layers of vegetation above. And the process is much more efficient on a steep slope.

“Gravity is basically preheating all the fuels ahead of itself on a steep slope.”

Crown fires are capable of moving quickly through dense forest—including those on the coast. Parts of the Interior, where the landscape is more open aren’t as conducive to such fires. (Those areas may see fast-moving, but cooler, grassland fires.)

Topography, climate, and tree density are also major factors in how fires are fought. Crews battling the fire near Hope were at the mercy of the environment before they could attack. Flatter ground in areas like the Interior means crews can have better access to sites and use heavy equipment while they work.

BC’s unique ecosystems means its forests can’t all be managed in the same way. One way to reduce wildfire risk is through fuel treatment, which can include pruning trees, thinning stands, and active removal of burnable material. The Fraser Valley Regional District, however, didn’t administer any treatment during the previous three wildfire seasons. (The Current wrote about that last year. You can read that story here.)

And unlike the Interior, controlled burns aren’t an effective fire management tool in the coastal region.

“One of the problems here is our options are kind of limited because the forests are so productive. In the interior, we can thin things out, and you can do prescribed burning,” Gray said.

“I don’t know what the solution is here.”

Gray is currently working on a project looking at how the province can better manage high severity burns. Subscribe to The Current to learn more about that project, and how we can mitigate health concerns around wildfires, in a future story.


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Joti Grewal

Reporter at Fraser Valley Current

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