Postfire debris-flow hazard assessments
Multi-site evaluation of a postfire debris-flow runout forecast method
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 dramatically alter how water moves across the landscape. After a fire, vegetation is removed and soil properties change, reducing the ground’s ability to absorb rainfall. As a result, even modest rainstorms can trigger dangerous flash floods and debris flows in steep burned areas.
Postfire debris flows are fast-moving mixtures of water, mud, rocks, and vegetation that can surge downslope like flowing concrete. These flows often move faster than a person can run and may travel far beyond the burned area, posing risks to people, homes, roads, and infrastructure. They are typically triggered by short bursts of intense rainfall and can occur during the first storm following a wildfire.
This project develops rapid methods to evaluate postfire debris-flow hazards and advances research on the processes that control their initiation and growth. The goal is to provide reliable scientific information that helps federal, state, and local agencies reduce risks and improve preparedness in recently burned landscapes.
USGS Postfire Debris-Flow Hazard Assessments
The USGS conducts postfire debris-flow hazard assessments for select fires in the western United States, assessing hundreds of thousands of acres of steep, burned terrain each year. These assessments use information about watershed characteristics, rainfall, and soil properties to answer a few key questions:
- Which burned watersheds are most susceptible to debris flows?
- What types of rainstorms could trigger debris flows?
- How much mud, rock and other debris are these flows capable of carrying?
- How far might debris flows travel?
Assessment results help watershed emergency response teams and other partners understand where debris flows could threaten downstream communities, roads, and infrastructure.
Use the links below to explore hazard maps, assessment data, and the software behind USGS postfire debris-flow assessments.
Hazard Maps
Access hazard assessment data
Software
Request a hazard assessment
Partners typically provide the data needed to conduct an assessment, but anyone may request an assessment for a relevant burned area.
Learn what information is required and how to submit a request for a hazard assessment.
Postfire Debris-flow Science
In addition to emergency hazard assessments, the USGS postfire debris-flow project collects data and conducts research to better understand debris-flow processes. This work supports the science behind current hazard models and helps guide future model improvements.
Project research also addresses key questions, including how long burned areas remain susceptible to debris flows and how far debris flows may travel beyond the burned area. Data and publications related to postfire debris flows are available using the tabs at the top of the page.
Use the monitoring, recovery, and runout links below to learn where we collect data and how ongoing research is improving our understanding of how burned areas recover and debris-flow runout mapping.
A postfire debris flow in the area burned by the 2016 Fish Fire, Los Angeles county, California. The flow was triggered by heavy rainfall on January 20, 2017.
Learn More
-
Postfire Recovery
“How long, after wildfire do I need to be concerned about debris flows in my area?” The USGS conducts research to evaluate the recovery of burned areas using field monitoring stations, satellite-based data, and numerical models. This work facilitates the development of USGS hazard assessment products that are geared to answer this question.
-
Postfire Debris-flow Runout
"How far will debris 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.
-
Postfire Monitoring and Data Collection
The USGS collects data after wildfires and following storm events to better understand debris-flow hazards and their impacts.
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 dramatically alter how water moves across the landscape. After a fire, vegetation is removed and soil properties change, reducing the ground’s ability to absorb rainfall. As a result, even modest rainstorms can trigger dangerous flash floods and debris flows in steep burned areas.
Postfire debris flows are fast-moving mixtures of water, mud, rocks, and vegetation that can surge downslope like flowing concrete. These flows often move faster than a person can run and may travel far beyond the burned area, posing risks to people, homes, roads, and infrastructure. They are typically triggered by short bursts of intense rainfall and can occur during the first storm following a wildfire.
This project develops rapid methods to evaluate postfire debris-flow hazards and advances research on the processes that control their initiation and growth. The goal is to provide reliable scientific information that helps federal, state, and local agencies reduce risks and improve preparedness in recently burned landscapes.
USGS Postfire Debris-Flow Hazard Assessments
The USGS conducts postfire debris-flow hazard assessments for select fires in the western United States, assessing hundreds of thousands of acres of steep, burned terrain each year. These assessments use information about watershed characteristics, rainfall, and soil properties to answer a few key questions:
- Which burned watersheds are most susceptible to debris flows?
- What types of rainstorms could trigger debris flows?
- How much mud, rock and other debris are these flows capable of carrying?
- How far might debris flows travel?
Assessment results help watershed emergency response teams and other partners understand where debris flows could threaten downstream communities, roads, and infrastructure.
Use the links below to explore hazard maps, assessment data, and the software behind USGS postfire debris-flow assessments.
Hazard Maps
Access hazard assessment data
Software
Request a hazard assessment
Partners typically provide the data needed to conduct an assessment, but anyone may request an assessment for a relevant burned area.
Learn what information is required and how to submit a request for a hazard assessment.
Postfire Debris-flow Science
In addition to emergency hazard assessments, the USGS postfire debris-flow project collects data and conducts research to better understand debris-flow processes. This work supports the science behind current hazard models and helps guide future model improvements.
Project research also addresses key questions, including how long burned areas remain susceptible to debris flows and how far debris flows may travel beyond the burned area. Data and publications related to postfire debris flows are available using the tabs at the top of the page.
Use the monitoring, recovery, and runout links below to learn where we collect data and how ongoing research is improving our understanding of how burned areas recover and debris-flow runout mapping.
A postfire debris flow in the area burned by the 2016 Fish Fire, Los Angeles county, California. The flow was triggered by heavy rainfall on January 20, 2017.
Learn More
-
-
Postfire Recovery
“How long, after wildfire do I need to be concerned about debris flows in my area?” The USGS conducts research to evaluate the recovery of burned areas using field monitoring stations, satellite-based data, and numerical models. This work facilitates the development of USGS hazard assessment products that are geared to answer this question.
-
-
Postfire Debris-flow Runout
"How far will debris 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.
-
-
Postfire Monitoring and Data Collection
The USGS collects data after wildfires and following storm events to better understand debris-flow hazards and their impacts.
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.