Have Wildfires Increased in Canada?

You’ll never guess. It’s complicated.
Helps to know people like Zeke Hausfather.

Zeke Hausfather in The Climate Brink:

How have Canadian fires changed over time?

The Canadian National Fire Database provides is a collection of forest fire data from various sources. Fires of all sizes are included in the database, but a small portion of fires (those greater than 500 acres) account for more than 97% of area burned in most years. The figure above shows both the number of fires and area burned in Canada since 1980.

Since 1980 the number of fires has declined notably, from around 8,000 fires per year in the 1980s to around 6,000 today. The total count of fires is more of an indicator of changes in ignitions (either human-caused or lightning-related), while the area burned is more reflective of fire conditions.

The overall area burned in Canada shows no clear trend, with a number of extremely high individual wildfire years in the 1980s and 1990s, but a small upwards trend since the early 2000s. Its unclear where 2023 will fall with respect to this longer record, but over 3.3 million hectares have already burned and the fire season has only just begun.

How might they change in a warmer world?

While it is hard to detect a clear signal in area burned in Canada to date, there are a number of studies suggesting that warmer conditions over the coming century driven by climate change will increase the prevalence of wildfires.

The figure below, from the IPCC 6th Assessment Report WG1, shows medium confidence of increased fire weather by the end of the century in both Eastern and Western Canada, as well as an upward observed trend in fire weather in the historical record Western Canada (though no clear trend to-date in Eastern Canada). The IPCC defines fire weather as weather conditions conducive to triggering and sustaining wildfires, based on a set of indicators including temperature, soil moisture, humidity, and wind.

A 2017 paper by Dr. Mike Wotton and colleagues found large and significant increases in the percent of fire weather days (where active fire growth potential exists) across different regions of Canada across three different Earth System Models. While this research used the high-end RCP8.5 scenario, a similar (but smaller) effect would occur under more plausible emissions scenarios.

A more recent 2021 paper by Dr. Xianli Wang and colleagues finds similar results, with a large increase in annual area burned, number of fires, and maximum fire size across Canada in a warming world, with a partially strong percent increase in Eastern Canada in the latter half of the 21st century.

Similarly, Wang et al 2020 finds that “across Canada an extreme fire year could be four times more common by the end of the century, and more than ten times more common in the boreal biome (assuming other factors remained constant). That is, an average fire year under the extreme climate scenario may burn ∼4 Mha more area than the most extreme fire year in Canada’s modern history (∼7 Mha). By accounting for the strong nonlinear expansion of wildfires as a function of number of fire spread days, even conservative climate-change scenarios yield significant increases in fire activity.”

While more attribution work still needs to be done to determine what – if any – effect climate change to-date has had on the current catastrophic wildfires sweeping through Canada, the scientific literature is clear that these sort of events are likely to become more common as the world warms.