There are fewer wildfires in Canada but they are more powerful

The wildfires that have ripped through parts of Western Canada this spring are part of an overall rise in more powerful fires, experts say. But the details behind this trend are more complex than just counting the fires, or damage done, per year. 

CBC News reviewed historical data to get a sense of the changing nature of wildfires, and the role of climate change, in the country. (Canada started collecting wildfire data in 1950, though that first decade's is thought to be less reliable.) 

The first chart shows that the number of annual wildfires has, in fact, been declining since the '80s.

Experts attribute that to improved fire prevention — so the number of human-caused fires is going down.

This is thanks to better education and fire bans, says Mike Flannigan of Thompson Rivers University in Kamloops, B.C., one of the country's foremost experts on wildfires, who also reviewed the data.

At the same time, the fires that break out now tend to burn more territory. Overall, the area burned annually by wildland fires has more than doubled since the 1970s, according to a recent federal report. 

The next chart shows the number of burned hectares by decade.

The trend is "not just a straight line. It's a bumpy path," Flannigan stressed.

"There is a large year-to-year variability because of weather and ignition." 

The recipe for a wildfire has three ingredients — ignition (either lightning or humans), fuel (dried grasses, shrubs, trees and other vegetation) and dry weather, he says.

But the particulars of those three ingredients are changing, along with the climate.  

In Canada, roughly half of all fires are now caused by lightning. But lightning strikes are on the rise and expected to further increase with climate change.

Because of climate change, the vegetation is more likely to be dry and more flammable.

"As the temperature increases, the ability of the atmosphere to suck moisture out of the fuel increases almost exponentially," said Flannigan.