Forest fires | Climate change puts an end to nighttime lulls

This study, co-authored by researchers from British Columbia and Alberta, indicates that the number of fire-prone hours has increased sharply in North America over the past 50 years, particularly in fire-prone areas of Western Canada.

Published Friday in the peer-reviewed scientific journal Science Advancesthis study highlights that much of Western Canada has experienced an additional four to five hours of fire-prone conditions each wildfire season over the past half-century.

In British Columbia and Alberta, this translates to approximately 200 to 250 additional hours of fire-prone conditions in current seasons compared to those in the 1970s, encroaching on the nighttime hours and once quieter spring and fall periods.

By mid-century, Canada’s record-breaking 2023 wildfire season could “quickly become the norm,” according to co-author Kaiwei Luo.

“Extreme fire seasons will quickly normalize if these daytime and nighttime constraints on fires continue to decrease or weaken,” says Luo, who conducted this research as part of his doctorate at the University of Alberta.

“So this means that once the fire starts, there are no night-time conditions to slow it down or stop it,” he adds.

Nights and mornings – times when temperatures are typically lower, humidity higher and winds calmer – can help slow the spread of wildfires and provide firefighters with crucial respite.

Even Canada’s most active areas experience on average only about nine hours of fire-prone conditions per day during fire season, according to the study.

But researchers say climate change, largely driven by fossil fuel emissions, is leading to a sharp increase in the number of days that can offer more than 12 hours, or even a full 24 hours, of conditions suitable for fires.

“Addressing these challenges will require innovative approaches to fire science and management that take into account the changing temporal dynamics of wildfires on an hourly scale,” says the study, co-authored by researchers from the University of Alberta, Thomson Rivers University and Natural Resources Canada.

Days with a risk of 24-hour fire conditions, once rare in northern Alberta and the Northwest Territories, have jumped 232 per cent since the 1970s in these regions of the boreal tundra forest, the study says. Days with more than 12 hours of fire-prone conditions increased by 80%.

Similar increases have been observed in temperate montane forests, notably in the interior of British Columbia and the Pacific Northwest of the United States.

Both Alberta and British Columbia have stepped up their nighttime aerial firefighting operations in recent seasons, equipping more helicopter pilots with night vision goggles.

Canada is warming about twice as fast as the global average, and even faster in the country’s north, in part because of the loss of snow and sea ice cover that acts as a shield reflecting solar radiation.

Other studies on the question

Other studies have looked at changes in the length and severity of wildfire seasons, but few have examined fire activity over a 24-hour cycle.

The same researchers behind the study published Friday published a paper in 2024 linking extreme fire activity at night to drought.

For this study, researchers analyzed hourly satellite data from 2017 to 2023 for nearly 9,000 wildfires across North America.

They found that 60% of these fires reached their peak intensity in less than 24 hours, and 14% reached their peak during the night.

The research team then trained a machine learning model on these recent hourly observations to estimate wildfire activity from 1975 to 2024 based on historical weather conditions.

The study suggests that, across the continent, the annual number of potential burning hours increased by 36% over those 50 years.

The absolute gains in potential burning hours were greatest in summer — peak wildfire season — but the generally quiet spring and fall seasons saw steeper relative increases, with increases of 57 and 48 percent, respectively, according to the study.