BOISE – The National Weather Service in Boise is warning of flash flooding in some burned areas of the Pioneer Fire.
“They're definitely going to have a chance of rain up in there,” said Troy Lindquiest, senior service hydrologist at the National Weather Service. “This may be more of a drawn out rainfall over a 24-hour period but it's still something we need to monitor.
Cooler temperatures and rainfall helped crews over the weekend to contain an additional four miles on the fire's perimeter, bringing total containment to 63 percent. But the change in weather also brings with it added risk in some areas.
“When we get into these forested areas that have been burned you not only have the steep terrain but the vegetation has been burned away,” said Lindquist. “It's mostly in the pine forest that we see this water-repellent soil. If you get the water-repellent soils, it can bead up just like water would on a freshly-waxed car.”
Lindquist says soil turns water repellent when a fire burns hot enough that forest litter, like pine needles and pine cones, is infused into the ground, creating a wax-like coating.
“The risk of flash flooding is definitely greater,” said Lindquist. “That can carry a lot of ash, a lot of burnt logs, branches and even rocks and stuff eventually and they can become very destructive.”
Lindquist says heavy rain can flood a burn zone like this in no time.
“[Floods] can develop really quickly, with very little warning time and be very destructive,” said Lindquist.
The National Weather Service urges people to use caution around the burn zone, especially during heavy rain.
“If they're downslope of a burned area or downstream of drainage from a burned area, they need to be aware that there may be an enhanced risk of flash flooding at their location,” said Lindquist.
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