Post-Wildfire Debris Flow Awareness

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Post-wildfire hazards in Colorado can be as?dangerous as the fires themselves.

Dennis Staley

USGS geologist Dennis Staley studies the Montecito area impacted after a Jan. 9, 2018 debris flow event. (Credit: Donyelle K. Davis)

This year, tens of thousands of fires burned more than 8.75 million acres across the West, which is about 2 million more acres than the 10-year average. Sadly, more than 80% of these wildfires were human-caused. Colorado was hit particularly hard by wildfires with the East Troublesome and Cameron Peak fires impacting numerous residents and Department of the Interior-managed lands such as Rocky Mountain National Park.

These fires damage property and uproot families, which is exactly why President Trump has taken bold actions to reduce wildfire risk and promote active management of our forests and rangelands throughout his presidency. The Department of the Interior’s wildland firefighter crews have worked expeditiously to ramp up preventative treatments across the nation covering a record 5.4 million acres of lands since 2017 and treating 1.5 million acres in 2020 alone. This has been accomplished while wildland firefighter crews also worked around the clock to control and put out ongoing fires throughout the country in a heroic effort to protect Coloradans and other Westerners.

However, the fight against wildfires is not simply a preventative one. What about after the fire occurs: what happens after the smoke clears? Fire not only destroys the vegetation; it can also alter landscapes by destabilizing slopes and baking soils such that they actually repel water. When a storm passes over a burned area, it may trigger post-fire debris flows and flash flooding, both of which can be particularly devastating for areas downslope.

A notable example of Colorado’s history of wildfire and post-fire hazards occurred in my hometown of Colorado Springs. The Waldo Canyon fire of 2012 forced the evacuation of over 32,000 people and destroyed over 29 square miles of forest lands and 346 homes. Tragically, two people were killed in this fire. Following the fire, rains above Manitou Springs generated a debris flood that swept through town destroying an access road to I-70 as well as numerous businesses and homes.

At the U.S. Geological Survey, the research arm of the Department of the Interior, our mission is to utilize science to safeguard all communities from natural disasters. We support emergency responders who work to keep people and communities safe, provide the resources that assess how landscapes change after a wildfire, and develop the tools necessary to forecast and prepare for possible threats.

Our USGS Landslide Hazards Program based in Golden, Colorado, delivers actionable information, risk assessments, and advice to emergency responders and other managers that can improve public safety regarding landslides, including those triggered after wildfires.

Much of the landslide program is located on the Colorado School of Mines campus, also home to our colleagues at the Colorado Geological Survey.

Post-fire debris flow assessments are typically completed toward the end of wildfire suppression efforts and in advance of forecasted heavy rainfall. Work is also underway to improve our assessments to not only identify drainage basins where debris flows will begin, but to also provide information on their path of travel and where they will end up.

Since 2015, the USGS has delivered more than 220 landslide assessments for wildfires covering more than 36 million acres — an area roughly the size of the state of Connecticut. This work has proved invaluable for emergency managers and evacuation planners, like the National Weather Service, which uses this information to guide its flash flood and debris-flow alerts. With advances in data analytics, we are constantly improving our knowledge and the dissemination of that knowledge to our most important customers: the citizens of Colorado and the rest of the Nation.

The post-fire debris flows that sometimes follow wildfires can have serious consequences, but you can reduce your risk. READYColorado has great advice on how to prepare before, during and after a wildfire and other hazards. If you want to learn more about USGS research, visit USGS Wildland Fire Science Program?and USGS Landslide Hazards Program.

Be safe. Be prepared. Be informed.

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