Nearly half of the North Carolina buildings that took on floodwater between 1996 and 2020 were not inside FEMA's mapped high-risk zones, according to a new University of North Carolina at Chapel Hill analysis. Researchers logged more than 90,000 structures that flooded at least once and flagged more than 20,000 that flooded repeatedly. The sheer volume of these off-the-map floods is enough to change how planners and homeowners think about risk.
The peer-reviewed paper reconstructed flood footprints for 78 damaging events and used address-level records and high-resolution geospatial data to estimate exposure. According to Earth's Future, the study trained random-forest models to predict flood damage at 30-meter cells and reported performance that outperformed some process-based and remote-sensing approaches.
"The FEMA 100-year flood plain is really the only public information most people have about their flood risk, but it is imperfect," said Helena Garcia, the study's lead author. Antonia Sebastian, a UNC hydrologist who advised the project, added, "Places that have flooded before will flood again." Those comments and local examples were reported by WRAL.
To build a statewide archive, the researchers combined National Flood Insurance Program claims with emergency-service records and geotagged social posts, then used the model to recreate flood footprints where damage records were sparse. Their approach identified roughly 90,000 buildings that flooded in at least one event and more than 20,000 that flooded multiple times, about double the count of repeatedly flooded buildings captured in federal insurance records, the authors write in Earth's Future.
What the Archive Means for Homeowners
The paper's dataset, an address-level archive of flood footprints, offers a far fuller picture of where water has actually reached than insurance claims or the older regulatory flood lines alone. "More information about where it has flooded in the past could help people make different decisions," Garcia told WRAL, whether that means buying a policy, elevating a home, or steering public mitigation dollars to hard-hit neighborhoods.
Why FEMA Maps Miss Risk
Part of the problem is baked into the system. FEMA's Flood Insurance Rate Maps were designed as a regulatory in or out tool for lending and building rules, not as a full spectrum of probabilistic risk. FEMA is rethinking that approach through its Future of Flood Risk Data initiative, which aims to provide graduated, probabilistic flood information to better inform planning and insurance decisions. FEMA says the effort will modernize mapping and expand non-regulatory products over time.
Even though the paper was published last year, its findings still show up in real life. Tropical Depression Chantal and other recent heavy-rain events have produced new rounds of inland damage and emergency declarations across central North Carolina. Governor Josh Stein declared a state of emergency for affected counties in July 2025 as communities dealt with record river crests and damaged infrastructure, underscoring the urgency of better exposure data. Governor's office
State Action and What Comes Next
State agencies are already building tools and funding projects that could use the UNC archive to target investments. The North Carolina Department of Environmental Quality's Flood Resiliency Blueprint has released mapping products and deployed millions in project funding to restore floodplains, retrofit streams and install nature-based storage, part of a broader push to put better data into planning and grant decisions. NCDEQ
For homeowners and local officials, the takeaway is blunt: being outside a regulatory flood line is not the same as being safe. The UNC archive will not stop storms, but it provides a repeat-flood map that planners, insurers and residents can use now, and it puts federal and state mapping programs on notice to catch up with the floods that are already happening.
