Wildfires burn away hillside vegetation and lead to flooding and debris flows (commonly called mudslides). With the official start of the monsoon season today, which is predicted to be wetter than normal, areas recently burned such as the area between Sedona and Flagstaff in the Slide fire, are at higher risk.
Local news reports on the results of the Burn Area Emergency Response (BAER) team evaluation indicate an 8-times greater risk of flooding as a result of the Slide fire. AZGS geologist Dr. Ann Youberg is our debris flow specialist and participates in BAER team assessments.
Similar hazards and risks exist across the Western U.S. A new online hazard assessment system was unveiled by the USGS last week that includes the Slide fire. It shows substantial areas with 60-80% probability of debris flows based on 10-year storms. A few small areas reach the 80-100% probability range.
[From the USGS explanation: The interactive map above displays estimates of the probability of debris flow (in %), potential volume of debris flow (in m3), and combined relative debris flow hazard. These predictions are made at the scale of the drainage basin, and at the scale of the individual stream segment. Estimates of probability, volume, and combined hazard are based upon a design storm with 10-year recurrence interval (i.e., a 1 in 10 chance of a storm of that magnitude occurring in any given year). Predictions may be viewed interactively by clicking on the button at the top right corner of the map displayed above. Visit the Scientific Background page for more information on how the predictions are calculated. For more information about what to do in case you live in an area where debris flows are possible, please visit If you live in a recently burned area, and there is a rainstorm…]
AGU blogger Alexandra Branscombe took a look at predicting post-fire mudslides in the Western U.S. at http://blogs.agu.org/geospace/2014/06/12/burns-floods-predicting-post-fire-mudslides-west/