Increased Debris Flow Risks - Resources - Golden Gate Weather Services

Increased Debris Flow Risks - Resources

With the strong likelihood of significant high-intensity rainfall over parts of North and Central California on Sunday and Monday comes the increased risk of debris flows (and flash flooding) in recently burned areas.

In the aftermath of a wildfire, there is a huge load of material deposited on the ground. Burned vegetation also changes the water balance of the denuded hillsides from wildfires by increasing the soil's water repellency. All of these factors combine for increased runoff of debris downslope.

Image: https://mcusercontent.com/204b7b5836feabf8f536d0226/images/fe96508f-39df-ca4d-47ba-b3a78b197e99.jpg

There are lots of variables, like vegetation type, slope, and rain intensity that ultimately determine the likelihood and impact of debris flows in each individual burn scar. The USGS produces very comprehensive analyses of these post-fire risks at https://landslides.usgs.gov/hazards/postfire_debrisflow/. However, the basic rules of thumb, mostly used operationally look at rainfall intensity and amount.
Image: https://mcusercontent.com/204b7b5836feabf8f536d0226/images/fffd1f1e-684b-df87-cb22-8535c60cc188.jpg

Other resources:
- https://www.wrh.noaa.gov/lox/hydrology/files/DebrisFlowSurvivalGuide.pdf
- https://www.weather.gov/riw/burn_scar_flooding

Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services
Phone: (650) 712-1876
Email: jnull@ggweather.com
Web: http://ggweather.com
Twitter: @ggweather

Jan Null

Jan Null has been a meteorologist in the San Francisco Bay Area for almost five decades and is frequently seen on television and heard on the radio when weather is in the news. Twenty-six years ago he founded a consulting firm, Golden Gate Weather Services, after a 24-year career with the National Weather Service. Mr. Null is a Bay Area native, having grown up in Oakland and lived in the East Bay until 2006 when he moved to Saratoga. He received a Bachelor of Science degree in Atmospheric Science from UC Davis in 1974 and his Master’s from San Jose State in 1992. Jan joined the National Weather Service in 1974 at the Weather Service Forecast Office in Redwood City. He worked as an operational forecaster throughout his career, including 13 years as Lead Forecaster. During his tenure at the NWS he also served as Meteorologist-in-Charge at the Center Weather Service Unit at the FAA’s Air Traffic Control Center in Fremont. He also did extensive research into the relationship between El Niño, La Niña and California rainfall and throughout his career he was a frequent media spokesperson for the agency. Jan has also been an Adjunct Professor and Lecturer at San Francisco and San Jose State Universities where he taught one evening a week for nearly 30 years. In 1998, Jan founded Golden Gate Weather Services, a consulting firm that specializes in forensic meteorology. He frequently serves as an expert witness in litigation where the weather is a factor. This often involves reconstructing past weather events or as his wife refers to it: “CSI Weather”. Mr. Null is also an internationally recognized expert of the sad topic of the heatstroke deaths of children in vehicles. After the death of a child left a vehicle in San Jose in 2001 he did a comprehensive study of vehicle temperatures that was ultimately published in Pediatrics in 2005. Since that time he has spoken at numerous national conferences and worked with a wide variety of child safety advocacy groups and agencies to raise awareness about the dozens of children who die from hyperthermia in hot vehicles each year. This data continues to be updated at NOHeatstroke.org. In his spare time he is a serious amateur photographer, specializing in wildlife and landscapes. Jan is married to Susan Hollis, a lifelong Saratoga resident and Realtor. He has two adult children in the Bay Area and the world’s most adorable 9-year old granddaughter and 4-year grandson.

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