 Traditionally, nighttime meant a reprieve for firefighters, with flames often weakening, at least somewhat, as the night grew cooler. But in recent years, about 20% of large wildfires stayed strong overnight. That's according to a study published in Nature. Author Kaiwei Luo says dry conditions are overpowering the effects of nighttime cooling. That means we have to use more resources. We need more people, more equipment.