North Carolina has experienced an unprecedented number of landslides, all triggered by the intense downpour from the remnants of Tropical Storm Helene. This staggering number surpassed the total landslides seen over the past two decades, prompting a change in strategy for risk mapping in the region.
David Korte, the program manager for North Carolina’s landslide hazards, shared these insights with the Governor’s Advisory Committee on Western North Carolina Recovery. He explained that the focus has shifted from traditional “hard landslide science” to a more holistic approach emphasizing resilience. “We moved to a focus of resiliency versus hard landslide science,” Korte stated, expressing hope that the updated maps will aid emergency managers in protecting infrastructure and planning evacuation routes.
The N.C. Geological Survey recorded 496 landslides due to Helene’s rains, a striking increase from the 358 landslides recorded from 1990 to 2023. Tragically, these slides resulted in the loss of 31 lives, with about 75% affecting roads, structures, or rivers.
Approximately 88% of the landslides occurred in areas that received at least 10 inches of rain, while none were found in locations with less than five inches. Korte mentioned that current science allows predictions of potential landslide areas a day or two in advance, although precise forecasting remains a challenge. “We’re not talking half an hour ahead of time. These are fast-moving landslides. They’re unpredictable, where they’re going to go,” he said.
Changing Mapping Priorities
Traditional landslide mapping involves identifying areas with historical evidence of slides, such as debris flows and rock falls. However, the existing maps display risk in too many locations, limiting their utility for emergency managers during storms.
The new mapping system under development will focus on areas projected to receive at least five inches of rain over 24 hours, using precipitation forecasts from the Weather Prediction Center. The aim is to identify “areas of concern” by integrating data from a developing network of precipitation and soil moisture monitoring stations.
“We’ll improve our susceptibility maps and remove as many false positives as possible over the next two years,” Korte said, highlighting the ongoing nature of landslide inventory efforts.
Utilization of Landslide Maps
Landslide hazard mapping funding has faced political challenges in North Carolina. In 2011, funding was cut amid concerns from developers, but was partially restored in 2017 with a $3.6 million allocation. Korte emphasized his goal is to highlight risk areas, leaving decisions on development to local officials.
“I’m leaving it up to others what to decide what to do with the property value assessments,” Korte remarked. Many local real estate agencies use the state’s map to disclose landslide risks to potential buyers.
In a recent disaster recovery bill, $3 million was allocated for mapping hazards in areas affected by Helene. The mapping team currently consists of three staff members, with plans to expand to include personnel for monitoring station maintenance. Korte noted the challenges in maintaining these stations due to interference from animals and vandals, and the need for more resources.
“Maintenance on those has been neglected because landslide mapping has been more important to our customers recently,” Korte explained, underscoring the need for a balanced approach to both mapping and monitoring efforts.
