If the expected rainfall on the eve of Thanksgiving day is intense enough, areas where the Woolsey fire burned would be more susceptible to mud flows than areas affected by the Camp fire, according to the U.S. Geological Survey.
USGS researchers created a map that shows the probability that different fire-affected areas will experience mud flows if there’s a storm that produces 24 millimeters of rain per hour, or a quarter of an inch in 15 minutes.
“We have historical information about where debris flows occurred, how big they were and the rainfall associated with triggering those events,” said Dennis Staley, a research geologist with the USGS. The model also considers slope steepness, topography and fire severity.
The dark red portions of the map indicate between an 80 and 100% chance of debris flows if rain reaches the assigned threshold for the map. Most areas affected by the Camp fire are colored yellow, indicating a 20% chance or less of debris flow. The Woolsey fire area on the other hand is mostly colored orange and red.
The reason for the higher probability, Staley said, is that areas affected by the Woolsey fire are steeper than where the Camp fire burned.
However, weather experts say rainfall in Southern California likely won’t be intense enough for dangerous mud flows. Rich Thomas, with the National Weather Service, said there will only be about quarter to three quarters of an inch of rainfall total.
There’s only a 10 to 20% chance the rain will become heavy enough to create mudflows, he said.
”There could be some minor debris flows, but nothing significant,” he said. “Rocks over the roadway, stuff like that.”