Common methods of communicating flood risk may create a false sense of security, leading 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 research scholar in NC State’s Center for Geospatial Analytics, said this may be an unintended byproduct of how the Federal Emergency Management Agency classifies areas based on their probability of dangerous flooding.
Known as flood mapping, this classification system describes areas in terms of their likelihood of being flooded each year. These classifications are then used to determine all kinds of regulatory requirements, such as whether a developer or homeowner must purchase flood insurance. For example, an area with a 1% chance of flooding in any given year would be referred to as a 100-year floodplain – and anything in the 100-year floodplain is designated “high risk.”
However, by designating the 100-year floodplain as “high risk,” regulators may unintentionally give the mistaken assumption that anything outside that zone carries no risk, Sanchez said.
“What our current methods do is draw a line between the 100-year floodplain, which is considered ‘high risk,’ and everything outside of it. We communicate flood risk in a way that says you are either on the ‘at risk’ side of that line, or the ‘minimal risk’ side,” Sanchez said. “If you are on the ‘safe’ side, then you are not required to purchase flood insurance or meet strict structural requirements. It then becomes more affordable to live just outside the floodplain, where the perceived risk is lower, yet you are still close to the beautiful lakes, rivers and coastlines we love.”
This, Sanchez said, creates a mechanism that clusters development just beyond the highest-risk flood areas, even though in reality the risk extends beyond the floodplain’s edge.
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 thus attracts increased development. This in turn leads to concentrated losses if a flood event exceeds what the flood-prevention structure was designed to withstand.
In focusing on regulatory floodplain mapping instead of these structures, Sanchez and her collaborators uncovered another example of the paradox, where efforts to reduce flood risk paradoxically intensify it by promoting development immediately outside of designated “high-risk” zones.