As the
death toll and number of missing continue to soar as a result of California's deadliest fire on record,
relief is finally on the way. But as we count our blessings this Thanksgiving, could the positive rainfall forecast bring too much of a good thing? Burn scars are especially susceptible to mudslides and debri flows. Hundreds of thousands of acres of recently charred ground will pose a major risk.
https://twitter.com/NWSLosAngeles/status/1064241768563175426
Let's break down the threat and how it could play out. First off, we have to understand the land prior to a debris flow.
![](https://media.weathernationtv.com/app/uploads/2018/01/1.jpg)
When dealing with an area of terrain that has vegetation, you're working with a certain depth of soil that is relatively strong and healthy. A healthy ground promotes more growth and sustains the growth that is already there. A
![](https://media.weathernationtv.com/app/uploads/2018/01/2.jpg)
After a period of extreme drought or after a wildfire, the ground becomes weak and vulnerable to any kind of water. When water flows over that ground - it becomes hydrophobic (A.K.A. water resistant). When this happens, the ground becomes solid like concrete. Here's a visual from the NWS in Boise, ID:
![](https://media.weathernationtv.com/app/uploads/2018/01/giphy-downsized-large-1.gif)
In the above video, water is poured onto a recently burned area. After the fire, the ground cannot absorb any of the water. It runs off, collects any loose debris, and heads downhill. Eventually coming to a halt downstream. When this happens in real life on a larger scale, boulders, trees, and other large debris get picked up and they become extremely dangerous.
![](https://media.weathernationtv.com/app/uploads/2018/01/3.jpg)
For more information about the dangers of debris flows and what causes them. Here's WeatherNation's John VanPelt:
https://www.youtube.com/watch?v=_If_zQSJTDI&feature=youtu.be
Interesting facts about debris flows:
~most common within 2 years of a wildfire
~normally range between 600 and 300,000 cubic meters. (about the size of a football field filled with 65 meters worth of mud and debris.)
~the size of the area burned, the gradient of the slope in which the burn happened, and the properties of the soil all contribute to how bad a debris flow can be
~rainfall conditions also play a crucial role (rain rate mainly - how much rain falls in a certain amount of time)
What should people who live near a burn scar do to protect themselves from potential flash flooding and debris flows?
Courtesy:
NWS
-Have an evacuation/escape route planned that is least likely to be impacted by Flash Flooding or
Debris Flows
-Have an Emergency Supply Kit available
-Stay informed before and during any potential event; knowing where to obtain National Weather Service (NWS) Outlooks, Watches and Warnings via the NWS Riverton website, Facebook, Twitter, or All Hazards NOAA Weather Radio
-Be alert if any rain develops. Do not wait for a warning to evacuate should heavy rain develop.
-Call 911 if you are caught in a Flash Flood or Debris Flow
For more information visit:
Debris Flow Info
For WeatherNation, Karissa Klos