The “safe development paradox” highlights how classifying land areas as “high risk” for flooding can unintentionally encourage high levels of risky development just outside of these zones. Though the risk continues beyond the high-risk label, the implication is that if an area is not listed as “high risk,” then it must be “safe.” This misconception arises from how flood risk is communicated and used to guide regulations, such as mandatory flood insurance and structural requirements. Building just outside of these “high risk” zones is more affordable, leading to clustering of development in areas that are still vulnerable to flooding from rivers, lakes, and coastlines.  

A new study, titled “The Safe Development Paradox of the United States Regulatory Floodplain,” analyzed national development trends and 100-year floodplain maps from more than 2,300 U.S. counties. Supported by the Southeast CASC, the researchers found that 24% of development occurs within 250 meters of high-risk flood zones. That distance is less than the length of three football fields, or, in a dense urban grid like Manhattan, about 1-3 city blocks. The researchers also looked at future projections, and assuming current policies remain the same, they predicted that 22% of new development by 2060 will also occur within the 250-meter zone next to the “high risk” area, likely increasing the number of people who live in risky areas just outside of the regulatory zone. 

By linking historical and future development trends to 100-year floodplain (1% annual flood risk) classifications that guide safety regulations, this national assessment reveals some unintended consequences of these designations and emphasizes the need to align actual and perceived flood risks. This information can aid regulatory agencies making flood risk designations and communications to support effective planning.  

This research was supported by the Southeast CASC Project: “Improving Scenarios of Future Patterns of Urbanization, Climate Adaptation, and Landscape Change in the Southeast.”