The Special Flood Hazard Area is defined as the area that will be inundated by the flood event having a 1% of being equaled or exceeded in any given year. These "high-risk" zones (Zone A, AE, AH, and AO) may experience very unusual or infrequent flooding, but do have a significant risk of suffering flood damage during the normal lifespan of most buildings. Over a typical 30-year mortgage period that 1% chance per year adds up to a very respectable probability. By comparison, as of 2011, the national averages show that a typical home over the same 30-year period only has a 1% chance of being damaged by fire for the entire 30 years. Yet almost everyone willingly buys fire insurance for protection from that hazard.
Past experience is one of a number of factors used when determining flood potential. Another factor that will significantly change your flood risk over time is the amount of new development that has occurred in your watershed which will increase the speed and quantity of the storm runoff and greatly increase the extent of flooding. Inadequate levees can be very effective for smaller storm events but may fail dramatically in places when faced by a really major storm. The flood hazard areas were determined using analyses of records of riverflow, storm tides, and rainfall; information obtained through consultation with the community and topographic surveys. The Flood Insurance Study also assumes the free flow of floodwaters through bridge openings and culverts. During an actual flood event, these openings may become plugged and other areas not shown as floodprone may be flooded.
This Flood Insurance Study represents the best technical information on the current flood risk in your community.