From the Document; "There is a large flood insurance gap in the United States, where many people that are exposed to flood risk are not covered by flood insurance. The National Flood Insurance Program (NFIP) is the primary source of residential flood insurance. More than 22,000 communities participate in the NFIP, with more than five million policies providing more than $1.3 trillion in coverage. The NFIP identifies areas at high risk of flooding as Special Flood Hazard Areas (SFHAs). Property owners are required to purchase flood insurance only if (1) their properties are in SFHAs, (2) their communities participate in the NFIP, and (3) they have federally backed mortgages. Because the SFHA boundary is central to NFIP mapping, it may create a false belief that flood risk changes abruptly at the boundary and that properties outside the SFHA are safe and do not need flood insurance. However, about 20% of NFIP claims are for properties outside SFHAs, and all 50 states and five territories have experienced floods since May 2018."
CRS Insight, IN10890
Congressional Research Service: https://crsreports.congress.gov/