Why is there a requirement to purchase flood insurance in communities that have not suffered flooding in many years, or ever?

A major purpose of the NFIP is to alert communities to the danger of flooding and to assist them in reducing potential property losses from flooding. Historical flood data are only one element used in determining a community’s flood risk. More critical determinations can be made by evaluating the community’s rainfall and river-flow data, topography, wind velocity, tidal surge, flood-control measures, development (existing and planned), community maps, and other data. Over time, additional development or changes in these factors can alter the flood risk, and flood maps may be revised.