How flood risks are classified can give developers and home buyers a false sense of security

Common methods of communicating flood risk create a false sense of security and can lead to increased development in areas threatened by flooding.

This phenomenon, called the “Safe Development Paradox,” is described in a new paper from North Carolina State University. Lead author Georgina Sanchez, a researcher at the North Carolina Center for Geospatial Analysis, said this may be an unintended byproduct of the way the Federal Emergency Management Agency categorizes areas based on their potential for dangerous flooding. said.

The results of this study are published in the journal PLOS ONE.

This classification system, known as flood mapping, describes areas in terms of the likelihood of flooding each year. These classifications are used to determine all sorts of regulatory requirements, such as whether a developer or homeowner must carry flood insurance. For example, an area with a 1% chance of flooding in a given year is called a 100-year floodplain, and anything in a 100-year floodplain is designated as “high risk.”

But by designating a once-in-a-century floodplain as “high risk,” regulators could inadvertently give regulators the false impression that there is no risk outside that zone, Sanchez said. he said.

“Our current approach is to draw a line between the 100-year floodplain and everything outside of it that is considered ‘high risk.’ “We communicate flood risk in a way that it’s either on the ‘minimal risk’ side of that line,” Sanchez said.

“If you’re on the ‘safe’ side, you don’t need to buy flood insurance or meet strict structural requirements. Then it’s better to live just outside the flood plain, where the perceived risk is lower. It’s more affordable, but you’re still close to the flood plains’ to the beautiful lakes, rivers and shorelines we love. ”

Sanchez said this creates a mechanism to concentrate development just outside the most at-risk flood areas, when in fact the risk extends beyond the edges of the floodplain.

Previous research on the safe development paradox has focused on the “levee effect,” where the construction of flood protection structures gives the false impression that an area is safe from flooding, thereby attracting increased development. Ta. This leads to concentrated losses in the event of flooding that exceeds the level that the flood protection structure was designed to withstand.

Sánchez and his collaborators focused on mapping regulatory floodplains instead of these structures, and found that efforts to reduce flood risk are located in the immediate vicinity of designated “high-risk” areas. We uncovered another example of the paradox in which promoting external development paradoxically enhances flood risk.

By overlaying floodplain maps of more than 2,300 counties with data on previous development trends and simulated future development, researchers found evidence of the safe development paradox from the national level to the county level. The study found that 24% of all development nationwide occurs within 250 meters of a 100-year floodplain, and that without new policies to prevent flood damage, this number will be at least It is predicted to continue increasing until 2060.

Although the study was concluded in 2019, these findings are also evident from the recent damage caused by Hurricane Helen in western North Carolina, Sanchez said.

“Places like western North Carolina have steeper terrain, so they’re more heavily developed than flat areas,” she says. “Developers tend to seek land that is flat enough to build on, often along river networks and close to flood-prone areas.

“When I watched the news after Helen and saw the footage from that area, I could really see the results of our research being reflected in those scenes.”