Nearly 43% of buildings that flooded in North Carolina between 1996 and 2020 were located outside of a federal agency’s official flood zones, according to a by researchers at The University of North Carolina at Chapel Hill.
The findings reveal that out of more than 90,000 buildings in the state, over 38,000 homes and businesses faced flood damage in areas not identified as high-risk on federal maps, leaving many residents potentially unaware as flooding becomes more frequent and severe across the state.
“We modeled 78 events, and we found that 44 of those 78 events were associated with tropical cyclone activity,†said Helena Garcia, graduate research assistant and lead author of the study at The University of North Carolina at Chapel Hill. “Of the 90,000 buildings flooded, a majority of the buildings, not just in coastal areas, were flooded by one of those 44 events with tropical cyclone activity. That really showed us that tropical cyclones have impacts further inland in the state, and it’s not just a coastal issue.â€
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The Federal Emergency Management Agency’s (FEMA) Flood Insurance Rate Map (FIRM) shows areas of flood risk across the U.S. The maps designate different flood zones, ranging from low- and moderate-risk areas to high-risk areas known as Special Flood Hazard Areas (SFHAs). Flood maps are usually updated every 5 to 10 years, based on new data about rainfall, rivers, development and changes in the land.
According to Garcia, while coastal counties receive more frequent updates, the process largely depends on government capacity.
“Mapping more regularly would definitely be helpful,†she added.
In addition to the need for more frequent and regular mapping, Garcia noted that while their study did not specifically examine the role of climate change in flooding intensity or frequency, they are aware of its potential impact.
“One thing we do know is that climate change is warming the atmosphere, making it hold more moisture, and this can lead to heavier and more intense rainfall events like the one we saw this week,†she said.
Antonia Sebastian, an assistant professor and flood risk researcher at the University of North Carolina at Chapel Hill, said the 43% figure is consistent with national trends, where about one-third of flood damages, and often more, occur outside of FEMA-designated flood zones.
“I wasn’t at all shocked by that number,†Sebastian said, noting that in some coastal areas or places with outdated maps the percentage can be significantly higher.
In of a Texas community, for example, about 75% of flood damages between 1999 and 2009 occurred outside the mapped 100-year floodplain. North Carolina’s numbers fall well within the expected range, particularly in regions exposed to hurricanes or undergoing rapid development.
Nonetheless, the extent of repetitive flooding in inland areas came as a surprise to the researchers.
“For example, Forsyth County, at least in the map, we do see a number of repetitive flooding communities in that area as well. It’s definitely more so on the coastal side, but we were surprised with how many inland counties had repetitive flooding also,†Garcia said.
Aligned with global trends, experts say North Carolina and the Triad can expect more frequent and intense hurricanes in the coming years, driven by climate change factors such as warming ocean temperatures, rising sea levels, increased atmospheric moisture, and slower-moving storms that bring prolonged rainfall and flooding.
The recent landfall of tropical depression Chantal in central North Carolina fits that trend, with experts noting that the event — considered a once-in-1,000-year occurrence — marked an unusually strong and early start to the hurricane season for the state.
Garcia also pointed to the role of urban growth and agriculture in shaping flood risk across the state, referencing a previous which found that for every property bought out in a floodplain in North Carolina, 10 new buildings were constructed in flood-prone areas.
“There’s definitely scales of mitigation and adaptation measures that could be taken so they could be taken by a local community figuring out where to put infrastructure, for example, to protect a community against flooding,†she added. “But also, homeowners can take different methods — people could elevate their home, and a lot of people have in North Carolina — but they can also think about flood proofing different things, like elevating mechanical systems in their home, for example.â€
