Recent drought conditions render longstanding fire management strategies ineffective

When a wildfire begins to rage, firefighters typically plan their counterattack based on the “active day, quiet night” fire cycle. This means that due to cooler and more humid conditions, the blaze tends to ease, and be easier to snuff out, after sunset. Worsening drought conditions, however, have transmuted this cycle, reports a study published last week in Nature. Fire management practices will need to adjust accordingly.

The last few years have been some of the most devastating wildfire seasons on record on the west coast of the United States. Throughout this period, a steady stream of research has confirmed what frontlines workers have experienced firsthand — that nighttime is no longer offering an opportunity to gain purchase on a fire hurdling past attempts at containment. A team of scientists in Canada have now pinpointed some of the causes of the increase in frequency and duration of overnight fires, which may help facilitate early detection and improved fire management, and lends more insight into how climate change is affecting wildfires in North America.

By identifying over 1,000 overnight burning events in 340 individual fires, the authors of the study found that 20% of large fires had at least one overnight burning event, and that one night of burning frequently lead to a second. But it was the availability of extremely dry organic matter — a wildfire’s accelerant of choice —that was the most important factor in predicting overnight burns. This finding links drought conditions directly to nighttime fire risk, as prolonged periods of severe dry weather is what causes said dry fuel to accumulate.

“Originally, I had thought that since nights are warming faster than days, higher temperatures and the associated lower relative humidity at night would lead to more overnight fires,” says wildfire expert Mike Flannigan, who co-authored the study. Their findings showed that although warming does play a role in enabling nighttime fires, it was the highly flammable residue left in the wake of drought that provides a superhighway of sorts for wildfires to blaze through under the cloak of night.

Despite a wetter than normal start to the year in California — the state most affected by wildfires — the western U.S. is still feeling ripples of a decades-long megadrought. “Nighttime burning has long been overlooked, says Kaiwei Luo, the study’s first author. “In a warmer and drier world, we can use daytime drought indicators to predict the night.” Learning more about how climate change and extreme weather events challenge current models of disaster preparedness and emergency management will hopefully lead to adaptations to better mitigate damage in the future.