Mapping landslide risk in the United States and Puerto Rico
Living in a landslide-prone region means facing the dangers and damage that may occur when a slope fails. Communities that understand their risk for such events can be better prepared to save both infrastructure and lives.
Susceptibility maps help with this by showing where terrain and environmental conditions may make landslides more likely. However, current U.S. susceptibility maps focus mostly on steep, high-risk areas, offering little detail on or underestimating risk for gently sloping regions. Such regions-including parts of North Carolina that were recently devastated by Hurricane Helene-can still experience landslides and are more likely than steeper areas to host infrastructure and other development.
Using a U.S. Geological Survey (USGS) database of 613,724 landslide events, Mirus et al. developed a high-resolution (10-meter grid size) map to detail the landslide hazard risk throughout all 50 U.S. states and Puerto Rico. (Other U.S. territories didn't have sufficient topographic data or landslide inventories to be included.)
By combining this national data set with high-resolution topographic data, the researchers developed four threshold models-a type of model that can help determine which combinations of factors lead to a particular outcome. In this case, the models used the relationship between slope (or steepness) and relief, or the difference in elevation between an area's highest and lowest points, to determine landslide potential. They then reduced the resolution to a 90-meter grid size to account for uncertainty at larger scales and tested how well each model could differentiate susceptibility in different landslide-prone areas.
The best-performing model captured 99% of recorded landslides. The researchers then ran the model using landslide data sets from specific states, based on an additional 172,367 events. The model performed well with these data sets, too, but it showed more variability by region. Using these outcomes, the researchers created a more accurate national-scale map that highlights areas at greater risk for landslides in the future.
The new map could become a valuable tool to boost hazard mitigations, particularly in regions where stakeholders are not yet aware of their landslide risk. Already, in the wake of Hurricane Helene, USGS has combined the hazard map with rainfall data from the National Weather Service to aid ongoing search and rescue operations.