North America's Wildfire Burning Hours Up 36% Over 50 Years as Nights Warm Faster Than Days

A new study published in Science Advances reveals that the number of hours in North America favorable for wildfires has increased by 36% over the last 50 years. This shift is primarily driven by warmer and drier nighttime conditions, removing the traditional 'break' that firefighters once relied upon. The findings indicate that climate change is fundamentally altering the behavior of wildfires by keeping them active through the night.

The Details

The research, published April 17, 2026, utilized weather satellite data to analyze nearly 9,000 large fires between 2017 and 2023. By correlating atmospheric data with fire status, researchers developed a model applied to data from the U.S. and Canada spanning from 1975 to 2026. The results show a significant expansion of fire-prone conditions, with days characterized by fire-favorable weather increasing by 44%, adding roughly 26 days to the annual calendar over the past half century.\n\nRegional impacts vary, but the increases are stark. California has seen 550 additional potential burning hours since the mid-1970s. The most extreme increases were recorded in central Arizona and southwestern New Mexico, where some areas are experiencing up to 2,000 more fire-prone hours per year. This trend is corroborated by NOAA data, which shows that since 1975, summer nighttime lows in the contiguous U.S. have warmed by 2.6°F (1.4°C), outpacing the 2.2°F (1.2°C) rise in daytime highs.\n\nThis lack of nighttime recovery is critical. According to lead author Kaiwei Luo of the University of Alberta, humidity at night no longer rebounds from daytime dryness as it once did. Xianli Wang of the Canadian Forest Service noted that while fires normally slow or stop at night, extreme hazard conditions now allow them to burn throughout the night. Wang added that this persistent heat stresses plants, increasing the fuel load and making forests more combustible.\n\nThese conditions have led to more frequent nighttime ignitions and active burns. Notable examples include the 2023 Lahaina fire in Hawaii, which ignited at 12:22 a.m., as well as the 2024 Jasper fire in Alberta and the 2025 Los Angeles fires. Wildland firefighter Nicholai Allen highlighted the danger of these nighttime events, noting the added chaos as frightened wildlife, including bears and mountain lions, flee the flames in the dark.\n\nRecent data underscores the scale of the problem. From 2016 to 2025, U.S. wildfires burned an average area the size of Massachusetts annually—approximately 11,000 square miles—which is 2.6 times the average seen in the 1980s. Canada's 10-year average is 2.8 times its 1980s average. As of March 2026, U.S. wildfires have already burned 127% more acreage than the 10-year average, with over 1.5 million acres burned from more than 15,000 starts.

Context

The mechanism driving this shift is linked to heat-trapping gases from fossil fuels. Cloud cover absorbs and re-emits heat at night, acting like a blanket that keeps nighttime temperatures higher. When nights remain warm, forests are unable to recover lost moisture; in some cases, it can take weeks for dead fuel to recover from a dry spell.\n\nThis loss of a nighttime cooling period creates a dangerous cycle. Fires that do not 'go to sleep' maintain their intensity and get a running start the following morning, making containment efforts significantly more difficult for ground crews. This is part of a larger trend in the Western U.S., where the average wildfire season is now 105 days longer than it was in the 1970s.\n\nFurther research published on April 16, 2026, in Science Advances highlighted the rise of 'synchronous fire weather days.' These are days when fire-favorable conditions occur across vast areas simultaneously. Such days nearly tripled from an average of 22 between 1979 and 1984 to over 60 in the 2023–2024 period, with more than 60% of this increase attributed to climate change.

What's Next

As nighttime temperatures continue to rise and humidity rebounds weaken, the window for firefighting containment is expected to shrink further. Experts like John Abatzoglou of UC Merced warn that the reliability of nighttime breaks is disappearing, meaning that fire behavior will become increasingly unpredictable and aggressive.\n\nEmergency management agencies will likely need to adjust their staffing and strategic planning to account for 24-hour burning cycles. This may involve increasing the availability of aerial assets and shifting crew rotations to manage the exhaustion associated with fires that no longer subside after sunset.\n\nFuture studies will likely focus on the intersection of these nighttime temperature spikes and the increasing frequency of synchronous weather events. The combination of longer seasons and more intense, non-stop burning periods suggests that acreage burned in North America could continue to climb well above historical averages.