Common methods of communicating flood risks can create a false sense of security, leading to increased development in areas at risk of flooding. The results are published in the journal PLOS ONE.
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 NC State’s Center for Geospatial Analytics, said it could be an unintended byproduct of how the Federal Land Management Agency Emergencies classify areas based on their likelihood of dangerous flooding.
Known as flood mapping, this classification system describes areas based on their likelihood of flooding each year. These classifications are then used to determine all kinds of regulatory requirements, such as whether a developer or owner must carry flood insurance. For example, an area with a 1% chance of being flooded in a given year would be called a 100-year floodplain, and anything within a 100-year floodplain is designated as “high risk “.
However, by designating the 100-year flood plain as “high risk,” regulators may unintentionally give the erroneous assumption that anything outside that area carries no risk, Sanchez said.
“Our current methods draw a line between the 100-year floodplain, which is considered ‘high risk,’ and everything outside. We communicate flood risk in a way that says you’re either on the ‘at risk’ side of that line or the ‘minimal risk’ side of that line,” Sanchez said.
“If you’re on the safe side, you don’t have to carry flood insurance or meet strict structural requirements. It then becomes more affordable to live just outside the flood plain, where the perceived risk is lower, while still being close to the beautiful lakes, rivers and coastlines we love.
This, Sanchez said, creates a mechanism that clusters development just beyond the most at-risk flood zones, even though in reality the risk extends beyond the edge of the flood plain.
Previous research on the safe development paradox has focused on the “levee effect”, in which the creation of flood prevention structures gives the false impression that an area is safe from flooding and therefore attracts a increased development. This in turn leads to concentrated losses if a flood exceeds what the flood prevention structure was designed to withstand.
-By focusing on regulatory mapping of floodplains rather than these structures, Sanchez and colleagues discovered another example of the paradox, where efforts to reduce flood risk paradoxically intensify it by favoring development immediately outside the floodplains. areas designated as “high risk”.
By overlaying floodplain maps of more than 2,300 counties with data on past development trends and simulated future development, researchers found evidence of the safe development paradox from the national to the county level. The study found that up to 24 percent of all development nationally occurs within 250 meters of a 100-year floodplain, and projections indicate that this number will continue to grow at least until in 2060 without new policies to prevent exposure to flooding.
Although the study ended in 2019, these results are apparent in the recent destruction caused by Hurricane Helene in western North Carolina, Sanchez said.
“Because of the steep topography in places like western North Carolina, there is an even greater concentration of development compared to flatter areas,” she said. “Developers tend to look for land that is flat enough to build on, which is often along watercourse networks and closer to flood-prone areas.
“When I saw the news after Hélène and looked at the images from the area, I could painfully see the results of our study reflected in these scenes. »
Related News :