Wildfires and Mudslides - Southern California

I blogged about the southern California wildfires yesterday and today I'll discuss a second whammy that may hit nearby communities and areas consumed by wildfires affecting resources and risk to human life downstream. The second whammy is the massive flooding and even mudslides. Since I am the "resident expert" among deaf and hard of hearing on providing information about Burned Area Emergency Response, fire fighting, and post-fire risk potentials. I will take the opportunity to provide a little information to those who may face a second whammy. Just don't do too many rain dances if you know what's good for ya.

Deaf, hard of hearing and hearing people impacted by the wildfires need understand that once a wildfire dies down does not mean the danger is over. It may only just begin since southern California's rainy season is from November to April with winter bringing heavy rain and wet snow. After the 2003 wildfire in southern California, there were numerous mudslides that have killed and injured people that year, including kids. The 2003 year fire burned over 740000 acres. This year's fire we could possibly see it easily surpassed.

People need to understand, especially deaf people, on just how serious these debris flows can become because of the sheer magnitudes in jump on the amount of loose sediment, ash and debris that can be dislodged in a rainstorm event. Rainfall amount and intensity do not have to be that much in order to see a wall of water and mud coming down a slope of a scarred mountainside. But typically after a wildfire the magnitude of a stormflow has the possibility of going as high as 4 orders of magnitude higher, which means as much as 10,000 times greater on volume flow. Volume of storm flow would be dependent on acreage burned, soil type, topography, slope steepness, extent on the severity of burned areas, rainfall intensity and rainfall duration. Although it takes less rainfall to trigger a debris flow from burned out watersheds than from unburned areas. In southern California, as little as 7 millimeters (0.3 inches) of rainfall in 30 minutes has triggered debris flows. The risk of debris flow usually last about two years while the mountainside regrow its grasses, trees, and shurbs. So don't sigh a big relief if nothing happened the first year. If you live close to one of the burned out mountain side you still have year 2 and sometimes year 3 before you can relax your guard. If that isn't enough, consider the prospect of post-fire landslides as well.

My experience span several years doing BAER work (7 altogether in New Mexico and Colorado), BAER Team Leader for a 67,000 acre fire and forest fire fighting in Washington, Idaho and North Carolina. I'm well qualified and knowledgeable in those subject areas.

Here's a good material on that subject from the US Geologicial Survey called "Southern California—Wildfires and Debris Flows" for those interested on learning these things as well as protecting yourself.


Debris flow video. Post-fire rainfall effect in 2003, California. Subtitled.
Note all the rocks that makes up the extra volume in a storm flow.