How many wildfires are started by arson? Your questions, answered

unrecorded Q&A: respondent your questions on wildfires and broadcast character

The idea for this story came from audience members, like you, who got in touch with us. Send us all of your questions about wildfires and air quality. We are listening: ask@cbc.ca

This year marks the second-worst wildfire season in Canadian history after 2023, according to the latest figures from the Canadian Interagency Forest Fire Centre (CIFFC) and Natural Resources Canada. Scientists and emergency responders warn that it is just a preview of what's to come as climate change accelerates.

Yes — and it's likely to get worse.

"We are getting longer, hotter and drier seasons around the world, but especially here in Canada. This means more intense wildfire seasons," Wagstaffe said.

The World Weather Attribution Group, a team of meteorologists, now instantly analyzes data from a weather event and determines how much climate change has impacted it. This helps in rapidly linking bad wildfire seasons around the world to climate change.

"These back-to-back historical seasons are becoming more common, and while I hesitate to call it a 'new normal' because that will continue to shift, unfortunately, this is our new reality," said Wagstaffe.

It's not as straightforward as you might think.

Canada primarily uses something called the Air Quality Health Index (AQHI). It gives a holistic view of air quality. There are monitoring stations across Canada that are calibrated by experts. Many of them are on the ground, literally pulling in air to analyze it.

They look at fine particulate matter, other harmful chemicals and low-level ozone.

They measure things like parts per million of air pollutants, and then all that data is combined into a single index number, the AQHI, so the public can understand what their health risk is on a given day. On that scale, anything 10 plus is considered very high risk.

We're learning that wildfire smoke is much worse for our health than we initially thought.

"The smoke from forest fires can linger in the air for quite a while, and it can travel a long distance," Wagstaffe said.

"Whether the source is in British Columbia, just south of the border, or even across the Pacific, smoke can get caught up in the jet stream and travel right across the country. We saw that this summer. People in Toronto were seeing smoke from fires in Manitoba."

A study published early September in the journal Nature estimates that 82,100 people died prematurely due to chronic smoke exposure from the 2023 wildfires.

Of those deaths, about 42,000 occurred in North America, with 33,000 in the United States and 8,300 in Canada.

Concrete statistics on wildfires caused by arson aren't readily available because they are lumped into the broad classification of human-caused fires. 

"In Canada, wildfires are caused almost equally by humans and lighting," Wagstaffe said.

The percentage of wildfires that are human-caused also varies widely among provinces. 

"We typically see more human-caused fires earlier in the season, before thunderstorm activity really picks up mid-summer into fall."

And it is important to note that human-caused fires have been declining since 1980, according to the Canadian Journal of Forest Research.

Among human-caused fires, only a fraction are due to deliberate arson. Most are accidental or inadvertent, caused by things like ATVs sparking in dry brush, campfires left unattended, discarded cigarettes, or even sparks from trains.

These are the types of fires we can prevent, especially early in the season.

It depends on several factors, including the type of forest, its geographic location and how severely it burned. If a fire only lightly scorched the forest floor, recovery can begin fairly quickly. But if the fire burned hot and deep, especially through an old-growth forest, regeneration can take decades or even centuries.

In many cases, you'll start to see signs of life — like hardy plants and ground cover — within the first year or two. Wildfires are, after all, a natural part of many ecosystems. In fact, the soil is often more fertile after a fire, which can help certain species bounce back faster.

However, not all forests return to their previous state. In some areas, especially those hit repeatedly or severely, the land may regenerate into grassland or shrubland, rather than returning to a fully forested state.

There's also the issue of residue. Smoke and ash can leave a film of grime or particulates on solar panels, which reduces their effectiveness. That means cleaning your panels becomes even more important during or after wildfire season to ensure they keep functioning properly.

"Once the smoke clears and the sun returns, your solar panels should resume normal operation," Lynch said. 

"However, whether we'll need to design more smoke-resilient panels in the future is an open question and this is exactly what we mean when we talk about adapting to climate change as it evolves."

It's not just the oil and gas industry or transportation anymore — forest fires are major contributors to air pollution.

"Canada is now one of the largest emitters in the world and that's largely due to forest fire emissions," Lynch said.

This makes air quality much worse, not just for Canada, but for the entire world.

"It's creating a feedback loop as more land gets scorched and more ash fills the air, making it harder for Canada to control these wildfires."

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