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North American Wildfires Are Burning Longer Into the Night, Study Finds
WASHINGTON – Wildfires across North America are increasingly burning through the night and starting earlier in the day, a shift linked to human-driven climate change that extends the hot, dry conditions fueling these blazes, according to new research published in Science Advances.
Historically, fires would wane or even extinguish at night as cooler temperatures and higher humidity set in. However, that natural respite is becoming rarer. The study reveals that the number of hours annually with weather favorable to wildfire in North America has surged by 36% compared to 50 years ago.
In California, this equates to roughly 550 more potential burning hours each year since the mid-1970s. Some of the most dramatic increases are seen in parts of southwestern New Mexico and central Arizona, where fire-prone conditions have expanded by up to 2,000 hours annually-the largest jump detected in the study, which covered both Canada and the United States. It’s important to note that while conditions are ripe for fires during these extended periods, it doesn’t mean fires are actively burning throughout all those hours.
Nighttime Fires Pose Greater Challenges
Fires igniting or persisting overnight present significant difficulties for firefighting efforts. Notable examples include the 2023 Lahaina fire in Hawaii, the Jasper fire in Alberta in 2024, and the Los Angeles fires in 2025. The Maui blaze notably began just after midnight.
University of California Merced fire scientist John Abatzoglou, who was not involved in the study, explained that these “overnight fires” gain momentum by not slowing down, making them tougher to suppress the following day. “Nights aren’t what they used to be – that is, more reliable breaks for wildfire,” he noted. “Widespread warming and lack of humidity is keeping fires up at night.”
Wildland firefighter Nicholai Allen, who also develops home fire prevention tools, highlighted the additional dangers of night firefighting, including encounters with wildlife like snakes, bears, and mountain lions, which are more active and agitated during fires.
A Longer Fire Season, Fueled by Warmer Nights
The study also found that the number of days with fire-prone weather has risen by 44%, effectively adding about 26 extra days of risk over the past five decades. This shift is driven primarily by warmer, drier nights and slightly increased winds, creating a longer and more dangerous fire season.
“Fires normally slow down during the night, or they just stop,” said Xianli Wang, co-author of the study and fire scientist with the Canadian Forest Service. “But under extreme fire hazard conditions, fire actually burns through the night or later into the night.”
Why Are Nights Getting Warmer?
Scientists have long recognized that human activities releasing greenhouse gases trap heat in the atmosphere, causing nights to warm faster than days. Increased cloud cover acts like a blanket, retaining heat overnight. According to NOAA, since 1975, summer nighttime lows in the contiguous U.S. have risen by 2.6°F (1.4°C), outpacing the 2.2°F (1.2°C) increase in daytime highs.
This persistent warmth also prevents nighttime humidity from rebounding as it once did, exacerbating dryness and fire risk. “Humidity at night doesn’t rebound from its daytime dryness like it used to,” said study lead author Kaiwei Luo, a fire science researcher at the University of Alberta.
Drought conditions compound the problem, drying out soil and vegetation, turning forests into tinderboxes. Warmer nights, especially during heatwaves, deny both humans and ecosystems the necessary respite to recover.
“It’s just a stress to the plants,” Wang said. “That also increases fuel load and makes fire burning easier.”
The Growing Scope of Wildfires
From 2016 to 2025, wildfires in the U.S. annually consumed an area roughly the size of Massachusetts-about 11,000 square miles-more than two and a half times the average burned area in the 1980s, according to the National Interagency Fire Center. Canada’s burned land area has increased nearly threefold over the same timeframe, per the Canadian Interagency Forest Fire Centre.
Syracuse University fire scientist Jacob Bendix, not involved with the study, described the findings as a “sobering reminder” of how climate change is driving increased fire potential across nearly all fire-prone regions in North America.
As the climate continues to warm, experts warn that longer, hotter, and drier conditions will likely intensify wildfire threats, demanding new strategies for prevention and response.
This report is based on research supported by multiple foundations. The Associated Press retains full editorial control over the content.