Weather constraints that once helped to suppress wildfires are weakening at a dizzying pace, according to new University of Alberta research that reveals increasingly erratic hour-to-hour burning and a collapse of the reprieve cooling nighttime temperatures once afforded firefighters.
Kaiwei Luo, a postdoctoral researcher in the Faculty of Agricultural, Life, and Environmental Sciences, builds on a 2024 study that first sounded the alarm on nighttime burning. In that earlier research, he warned that because of drought, wildfire fighters could no longer depend on cool nights to stall the now-tireless march of a wildfire's destruction. He famously noted then, "The night might not save us."
With this new research published this week in Science Advances, Luo shows that climate change is weakening the day-night weather rhythm that once helped restrain wildfires, not only extending burning hours but increasingly amplifying fire behaviour hour by hour - a shift that explains the fast-escalating dynamics behind recent extreme fires and fire seasons.
In a paper, Luo and his colleagues combined seven years of satellite fire observations with 50 years of climate data to reconstruct historical fire potential. In doing so, the team found that weakened constraints of the day-night weather cycles are making wildfires burn longer, hotter and harder.
To understand the scale of this change, Luo's team modelled "potential burning hours," which are the hours in a day when local fire-weather conditions - often hot, dry and windy - are modelled to support active burning. Based on around 9,000 large fires that burned between 2017 and 2023, Luo and his team were able to extrapolate 50 years of potential burning hours.
What he found was that in the boreal forests of Western Canada - including Alberta, British Columbia and the Yukon - the number of potential burning hours has surged by between four and five hours annually for a total of nearly 250 hours over the last five decades.
"That is roughly equivalent to more than 10 additional days' worth of weather conditions conducive to continuous, day-and-night burning, compared with 50 years ago," explains Luo. In the subtropics and deserts of the United States, the gain is even more dramatic: across much of the Southwest, burning potential has risen by roughly 13 to 14 hours per year on average, with some localized hotspots approaching 40 hours annually.
This isn't just a statistical trend. Luo says it is a reality that has played out in recent tragedies. Luo points to the 2024 Jasper fires and the 2025 Los Angeles fires, which illustrated the stakes of increasingly erratic wildfire behaviour. Across North America, some recent fires have spread tens of kilometres within hours or sustained weeks of overnight burning.
The study found that 60 per cent of fires now reach their peak intensity within just 24 hours of starting. The research also revealed one-third of active fire days exceed 12 continuous hours of burning in fire-prone areas. Luo says this relentless pace already leaves no room for emergency services error or recovery.
"We have heard the big numbers, like around 30 million hectares burned across Canada between 2023 and 2025," says Luo, who notes the annual average is between two million and three million hectares lost to wildfire in Canada annually. "But what we find here is that the fire is being amplified every single hour. This explains what is going on behind those figures."
Luo adds the drivers behind this shift are a "warming climate" and "asymmetric diurnal warming," which is essentially a lingering dryness that prevents the air from recovering its moisture at night.
For fire management agencies, the implications are dire. Luo says if the "active day, quiet night" cycle disappears, the window firefighters use to get ahead of the flames will slam shut. He suggests that we must move toward innovative, hourly-scale forecasting and increase resources for firefighters who no longer get relief after sunset.
"The environment is already set," Luo warns. "That means we need to reduce fuel loads where possible and adapt fire manageement to a world with fewer overnight breaks. These fires just need a fuse."
