Under cover of night is when firefighters perform some of the most essential work of starving a wildfire. They can lay out sprinklers, directly attack smaller fires and run heavy equipment with less risk that it will overheat.<\/p>\n
But Canadian firefighters are observing a trend of high overnight temperatures that have brought on a new hardship: the 24-hour fire cycle.<\/p>\n
\u201cIt is relentless,\u201d said Randy Schroeder, a fire chief in the western province of Alberta. \u201cThe fires grow and last a lot longer than they would have normally done in the same fuel, in the same period of time, years ago.\u201d<\/p>\n
Ordinarily, when temperatures drop and humidity rises after dark, fires burn less intensely and spread more slowly, giving firefighters a window to control flames, as well as time to rest before fire activity picks back up the next day.<\/p>\n
But climate change is turning that on its head. As fire intensity increasingly remains high overnight, fire teams have been forced to rethink how they work.<\/p>\n
Maintaining the same schedule through the night also drives up the cost of fighting wildfires, said Mr. Schroeder, former president of the Alberta Fire Chiefs Association. And if crews can\u2019t attack the fire after dark, he said, \u201cWe have to basically get out of its way.\u201d<\/p>\n
More than 850 wildfires<\/a> were burning in Canada on Thursday, with the most active ones north of Lake Superior in Ontario. About 15 communities there have been evacuated near Thunder Bay.<\/p>\n Smoke from the fires has spread across the region<\/a> and into the United States, pushing the Air Quality Index well above 500 in parts of Ontario and the Midwest. The scale runs from 0 to 500, and anything above 300 is considered hazardous.<\/p>\n \u201cCool nights are so key to help get on top of some of these fires,\u201d said Liam Buchart, a fire weather meteorologist based in Edmonton. \u201cWhereas some of these nights \u2014 in this heat wave that\u2019s just moved through the region \u2014 have remained incredibly warm,\u201d he said. Overnight temperatures have at times hovered at 91 degrees Fahrenheit.<\/p>\n Wildfires are typically most active during the hottest parts of the day. But research has shown that across North America, they are increasingly burning earlier in the morning and later into the night, a side effect of the hotter, drier weather that fuels them.<\/p>\n Xianli Wang, a fire research scientist for the Canadian Forest Service, was the coauthor of a 2026 study<\/a> that used satellite data and computer modeling to estimate that potential burning hours in North America increased 36 percent from 1975 to 2024. Most of that increase came at night.<\/p>\n \u201cThe problem is that under increasingly extreme fire conditions, this nighttime slowdown is becoming less reliable,\u201d Mr. Wang said. \u201cFires can remain active well into the night, reducing the time firefighters have to contain them and leaving communities with less time to prepare or evacuate.\u201d<\/p>\n