Why has the Government designated these flood zones?

In an effort to protect property owners from the material and financial devastation of natural disasters, the federal government has implemented various "protection" programs, of which the National Flood Insurance Program (NFIP) is one. Through careful studies of communities across the United States, the government has identified specific flood prone areas, known as Special Flood Hazard Areas (SFHA), and now mandates proper insurance within those flood hazard zones.