Postfire debris-flow hazard assessments
2024 Elk Fire
Bighorn National Forest, Wyoming
2021 Muckamuck Fire burn area
Okanogan County, Washington
2020 Cameron Peak Fire burn area
Roosevelt National Forest, Colorado
2020 Dolan Fire
Los Padres National Forest, California
Wildfires can significantly alter the way water interacts with the landscape to the extent that even modest rainstorms can produce dangerous flash floods and debris flows. Recent fires in the western U.S. have impacted hundreds of thousands of acres of steep land, much of it public, making it susceptible to increased erosion and debris-flow activity. With the risk of severe wildfires continuing to rise and more development happening in fire-prone areas, it’s important to develop tools to understand the potential hazards posed by debris flows in recently burned areas.
This project aims to create quick and accurate ways to evaluate postfire debris-flow hazards. It also uses applied research to better understand the processes that control post-fire debris-flow initiation and growth. Federal, state, and local agencies need reliable scientific information about these hazards to help reduce the impact of wildfires on people, their homes, and the environment.
What is a postfire debris flow?
Debris flows, sometimes called mudslides by the media, carry much more than just mud. They are concrete-like mixtures of mud, water, boulders, vegetation, and other debris that move downslope faster than a person can run. They may travel great distances outside of the burn area, posing a significant risk to life and property.
Burned landscapes are particularly susceptible to debris flows because wildfire removes vegetation and alters soil properties, decreasing the ground's ability to absorb rainwater. These changes to the landscape mean that rainfall can runoff almost instantly, picking up mud, trees, and boulders as it travels downslope. The addition of debris to the rainwater increases the height of the flows, making them more dangerous and destructive than flash floods.
Debris flows are triggered intense bursts of rainfall and can happen during the first few minutes of the first storm following a wildfire.
A postfire debris flow triggered by intense rainfall on January 20, 2017, in the area burned by the 2016 Fish Fire, Los Angeles County, California.
USGS Postfire Debris-Flow Hazard Assessments
The USGS conducts postfire debris-flow hazard assessments for select fires in the Western U.S. These assessments use information about watershed properties, rainfall characteristics, and soil properties to answer a few key questions:
What burned watersheds are most susceptible to debris flows?
During what types of rainstorms are debris flows likely to be triggered?
How much mud and other debris are these flows capable of carrying?
Click the image below to access the postfire debris-flow hazard assessment dashboard. You can use the dashboard to view or download the data for all recent postfire hazard assessments conducted by the USGS.
More information about hazard assessments
Frequently asked questions
Scientific Background
GIS Services
Request an assessment
Learn more about postfire debris flows
RECOVERY
How long does the hazard last?
As the burn area recovers and the landscape returns to prefire conditions the level of debris-flow hazard decreases. Understanding this recovery process and how debris-flow hazards change in the years following the fire is an active area of research at the USGS.
Use the link below to learn more about fire recovery and postfire debris flows.
RUNOUT
How far can flows travel?
Understanding how far debris flows can travel and what the impacts may be is one of the most important questions we face to effectively protect life and property from debris-flow hazards.
Use the link below to learn more about debris-flow runout research at the USGS.
MONITORING
How well do our hazard models work?
Monitoring stations are installed in select burn areas to better understand the processes that control postfire debris-flow initiation and growth.
Use the link below to learn more about postfire watershed monitoring at the USGS.
Below is a list of science sites associated with this project.
Scientific Background
Postfire Debris Flow Science Infographic
Post-wildfire debris flow: 2016 Fish Fire, Las Lomas Canyon
The June 2016 Fish Fire burned over 12 km^2 in Los Angeles County, California. After the fire, the USGS installed an automated rain-triggered camera to monitor post-wildfire flooding and debris flow in a small canyon above the Las Lomas debris basin in Duarte. This video shows the peak flow triggered by an intense rainstorm on January 20, 2017.
Wildfires can significantly alter the way water interacts with the landscape to the extent that even modest rainstorms can produce dangerous flash floods and debris flows. Recent fires in the western U.S. have impacted hundreds of thousands of acres of steep land, much of it public, making it susceptible to increased erosion and debris-flow activity. With the risk of severe wildfires continuing to rise and more development happening in fire-prone areas, it’s important to develop tools to understand the potential hazards posed by debris flows in recently burned areas.
This project aims to create quick and accurate ways to evaluate postfire debris-flow hazards. It also uses applied research to better understand the processes that control post-fire debris-flow initiation and growth. Federal, state, and local agencies need reliable scientific information about these hazards to help reduce the impact of wildfires on people, their homes, and the environment.
What is a postfire debris flow?
Debris flows, sometimes called mudslides by the media, carry much more than just mud. They are concrete-like mixtures of mud, water, boulders, vegetation, and other debris that move downslope faster than a person can run. They may travel great distances outside of the burn area, posing a significant risk to life and property.
Burned landscapes are particularly susceptible to debris flows because wildfire removes vegetation and alters soil properties, decreasing the ground's ability to absorb rainwater. These changes to the landscape mean that rainfall can runoff almost instantly, picking up mud, trees, and boulders as it travels downslope. The addition of debris to the rainwater increases the height of the flows, making them more dangerous and destructive than flash floods.
Debris flows are triggered intense bursts of rainfall and can happen during the first few minutes of the first storm following a wildfire.
A postfire debris flow triggered by intense rainfall on January 20, 2017, in the area burned by the 2016 Fish Fire, Los Angeles County, California.
USGS Postfire Debris-Flow Hazard Assessments
The USGS conducts postfire debris-flow hazard assessments for select fires in the Western U.S. These assessments use information about watershed properties, rainfall characteristics, and soil properties to answer a few key questions:
What burned watersheds are most susceptible to debris flows?
During what types of rainstorms are debris flows likely to be triggered?
How much mud and other debris are these flows capable of carrying?
Click the image below to access the postfire debris-flow hazard assessment dashboard. You can use the dashboard to view or download the data for all recent postfire hazard assessments conducted by the USGS.
More information about hazard assessments
Frequently asked questions
Scientific Background
GIS Services
Request an assessment
Learn more about postfire debris flows
RECOVERY
How long does the hazard last?
As the burn area recovers and the landscape returns to prefire conditions the level of debris-flow hazard decreases. Understanding this recovery process and how debris-flow hazards change in the years following the fire is an active area of research at the USGS.
Use the link below to learn more about fire recovery and postfire debris flows.
RUNOUT
How far can flows travel?
Understanding how far debris flows can travel and what the impacts may be is one of the most important questions we face to effectively protect life and property from debris-flow hazards.
Use the link below to learn more about debris-flow runout research at the USGS.
MONITORING
How well do our hazard models work?
Monitoring stations are installed in select burn areas to better understand the processes that control postfire debris-flow initiation and growth.
Use the link below to learn more about postfire watershed monitoring at the USGS.
Below is a list of science sites associated with this project.
Scientific Background
Postfire Debris Flow Science Infographic
Post-wildfire debris flow: 2016 Fish Fire, Las Lomas Canyon
The June 2016 Fish Fire burned over 12 km^2 in Los Angeles County, California. After the fire, the USGS installed an automated rain-triggered camera to monitor post-wildfire flooding and debris flow in a small canyon above the Las Lomas debris basin in Duarte. This video shows the peak flow triggered by an intense rainstorm on January 20, 2017.