"The new method reduces unnecessary warnings without missing more landslides."
Event
In August 2020, the Grizzly Creek fire burned over 30,000 acres around Interstate 70 in Colorado's Glenwood Canyon. The following summer, rainstorms triggered debris flows that closed the highway for weeks. In 2022, despite officials anticipating further debris flows, none occurred as vegetation recovered.
Research Update
Andrew Graber, a landslide hazards research geologist at the USGS, led a study published in Geosphere that developed a new method for predicting postfire debris flows. The method incorporates satellite imagery to measure vegetation recovery after fires.
The updated equations were tested against three years of rainfall data in 12 burned areas. The predictions showed improved accuracy compared to pre-update forecasts, which Graber noted were based on worst-case scenarios immediately after a fire.
Statements
Graber stated that the new method reduces unnecessary warnings without missing more landslides. He cautioned that no forecast is perfect, but the improvement should help alleviate concerns about too many warnings.
"No forecast is perfect, but the improvement should help alleviate concerns about too many warnings."
Background
After a wildfire in steep terrain, factors such as soil changes and lack of vegetation increase debris flow hazard. USGS provides postfire hazard maps and rainfall thresholds to agencies like the Colorado Department of Transportation for decision-making on highway closures.