The wildfire season of 2023 was like no other in Canada’s history.
With roughly 18.5 million hectares of Canadian land burned, this year was the worst wildfire season ever recorded. It surpassed the previous record of 7.6 million hectares scorched in 1989.
Wildfires leave a mark and their side effects can be felt in future extreme weather events, which could play out as early as this spring, some experts say.
“If we’ve got larger or more frequent severe climate-associated disturbances in the landscape … the likelihood of having intersecting landscape disturbances becomes higher,” said Uldis Silins, professor of forest hydrology at the University of Alberta.
“So that notion of flooding after fire or fire after severe flooding, these are the kinds of things that we’re likely to see more of in the future. They’re ones that, frankly, we have very little experience with.”
Wildfires can change the characteristics of the landscape in ways that influence future extreme weather events, John Pomeroy, Canada research chair in water resources and climate change, told Global News.
When wildfires occur, the loss of the tree canopy leads to a much denser snowpack, he explained. The needles and branches that hold the snow back no longer exist, so more snow accumulates on the ground.
That snow also melts faster as it receives more sunlight given there’s less shade provided by the canopy above it, Pomeroy added.
“In places where soils freeze, they tend to freeze in a saturated state after a fire because any rainfall after the fire season just infiltrates into the soil, increases soil moisture, but it doesn’t go into transpiration through the trees because they’re dead,” he said.
Silins, who studies the impact of wildfires on water resources with a focus on the Rockies, said he’s noticed that snowmelt over burned lands is happening earlier in the year.
“We tend to see not only greater flow produced after fire, we tend to see earlier runoff and that’s being driven by those bigger snowpacks ripening earlier because the sun radiation is getting to them,” he said.
Oversaturated soils lead to runoff, and in places where fires have been really severe, “hydrophobic conditions” can be created in the soils, Pomeroy said.
Hydrophobic conditions, he explained, are created when the soils are somewhat baked and water can’t enter them very easily. These conditions can develop almost immediately after a serious fire, and while they’ll eventually recover, when they’re in that hydrophobic state, they pose a risk.
“When the next wet season hits … it can destabilize the soil if it’s on a slope and cause mudslides, but more commonly, it restricts entry of further water into the soil, and then we get more runoff and a greater probability of flooding occurring,” Pomeroy said.
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“That’s where we have to be very watchful for the flood season, which is typically in the spring and early summer, and if we do get a wet year, then we’ve got a higher risk of flooding.”
It’s unclear what spring across Canada will look like right now, but winter in Canada will be impacted by the El Niño weather pattern.
In his winter preview, Global News’ Chief Meteorologist Anthony Farnell breaks down what winter will look like across the country.
In British Columbia, where wildfires burned more than 2.84 million hectares of land this year, mild Pacific air will dominate the weather pattern.
B.C. was affected by floods, mudslides and landslides when about a month’s worth of rain fell on parts of the province in about two days in November 2021. That year, 869,270 hectares of land was burned by wildfires.
In the Prairies, the weather will be more variable than normal with wild swings in temperature. Snowfall will likely be below seasonal in Alberta and Saskatchewan and closer to average in Manitoba, Farnell wrote.
In Ontario and Quebec, El Niño winters in these regions are variable, with weeks of above-seasonal temperatures followed by shorter-duration cold spells. And in Atlantic Canada, temperatures will likely remain seasonal to even well below seasonal.
“Forest soils, when they’re not burned, are great water holders. Those soils act as sponges, they fill up in spring and then they release water more slowly over the summer, but after they’ve been burned, that organic layer is gone,” Pomeroy said.
“That’s the spongy moss layer that you notice walking through a forest, and it’s often right down to clay or silt that’s just been baked on the top. That shields water very easily, and it just forms runoff and flushes very rapidly into the streams.”
Wildfires are also changing the landscape in higher elevations, Silins said.
While forests at lower elevations generally are able to regenerate well after a fire, grass and shrubs are starting to replace them in higher elevations, he said.
“Very few tree seedlings have established there because so much of it was consumed in that particular severe fire, and that’s one of the issues forest ecologists worldwide are concerned about, he said.
“If we see an increase in the severity of the most severe fires, there is the possibility that it will impact the ability of those forests to regenerate. It’s not that those forests are destroyed, but it may take those forests much longer to recover than we might typically expect under historic burning conditions.”
Pomeroy added that even as those forests regenerate, they don’t manage water as well as the older trees that were there before.
And if they’re replaced by grass or shrubs, the hydrological behaviour of those watersheds will change.
“Their flood frequency and their water management needs will be completely different,” he said.
“We need to be able to plan for that to ensure that the communities downstream are still in safe locations, and we may have to manage that water very differently to accommodate the changed hydrology that’s occurring post-fire.”
Aside from anticipating more extreme weather events influenced by wildfires, Silins said municipalities either in or near a forest setting can better prepare for wildfires by managing fuel loads, and managing the state and condition of the forests near them.
Pomeroy said Canada needs better flood and drought prediction models.
“For instance, we know that after a forest fire, the risk of flooding is higher if heavy rain or snow melt were to occur. But in fact, most models do not have this built into them and they can’t reflect that risk,” he said.
“We have to develop more sophisticated and, hopefully, national modelling systems that can incorporate these changing land covers, changing fire risks into our flood forecasting models, and also into drought forecasting models because the change behaviour of a forest after a fire means that it has very different soil moisture characteristics and that prediction of drought also allows us to predict future fire risk.”
In September, Emergency Preparedness Minister Harjit Sajjan said Ottawa was considering how to tackle future extreme weather events in the wake of the fires.
However, he did not reveal specifics.
“We’re looking at all different types of disasters, doing the lessons learned and we’ll come out with the appropriate response,” Sajjan said on Sept. 7.
After this year’s wildfires, Pomeroy fears the worst.
“I expect the extremes of flood, drought and wildfire to continue to increase and create emergencies (like this summer) that we have never experienced in our lifetimes, and eventually in all of humanity’s existence,” he said in an email.
— with files from Global News and The Canadian Press