Wildfire activity generally slows at night as winds die down, temperatures drop and humidity rises. But a new study suggests that's changing.

U.S. Forest Service researchers examined data from heat-sensing satellites dating back to 2003, and found that increases in nighttime fire activity outpaced daytime increases.

The study's lead author, Patrick Freeborn, based at the Rocky Mountain Research Station in Missoula, Mont., says his team's findings raise safety concerns for firefighters.

"Nighttime fire activity limits the opportunities for firefighters to rest and recover," Freeborn said. "And then if and when they are conducting nighttime operations, they're exposed to the additional risk of working in the dark."

That additional risk was made plain last month when a rare nighttime firefighting mission near Estes Park, Colo., resulted in the death of an air tanker pilot.