Flood Inundation Hazard
Mitigation Application Online

The ability to look days into the future to see how many city blocks and roads might be flooded is becoming clearer with Flood Inundation Mapping. The National Oceanic and Atmospheric Administration's (NOAA) National Weather Service (NWS) and its National Ocean Service (NOS) Coastal Services Center (CSC) are collaborating with the Federal Emergency Management Agency (FEMA), and other partners, to develop inundation maps for inland freshwater flooding. Sets of maps (referred to as libraries) are being developed which include map layers depicting the spatial extent and depth of water for various flood levels ranging from minor flooding all the way through the flood of record in the vicinity of NWS river forecast locations. These new flood hazard graphics will help emergency managers and impacted citizens be better prepared to make important decisions regarding evacuations, moving property, and other mitigation efforts.

“Flood forecast maps take us into the next generation of flood forecasting to saves lives and property,” stated Glenn Austin, Chief of the NWS' Hydrologic Services Division. “ These new flood inundation graphics open the door to a new world of visual information coupling technology and science to produce 21st century services.”

Combined with traditional NWS river forecasts and flood bulletin information, these new flood maps show the areas of likely inundation based on current conditions and future rainfall. Maps are produced using geographic information systems (GIS) and datasets created in the production of FEMA's Flood Insurance Rate Maps. These libraries are accessible via the Advanced Hydrologic Prediction Service (AHPS) web portal, the NWS' engine that hosts its vital river and flood forecast information. In addition to displaying inundation maps using the NWS' web interface, decision makers can download these inundation maps and related data for use in their GIS applications (see http://www.weather.gov/ahps/inundation.php)

“This mapping initiative moves beyond the text descriptions to maps of the areas inundated at various flood stages,” Paul Rooney, Department of Homeland Security/FEMA Risk Analysis Branch . “This provides a much better understanding for both the local government and others of the risk in the area mapped because it shows impacts for a number of scenarios other than the 100-year flood. It is useful both for mitigation planning and for response purposes.”

In response to Hurricane Floyd's devastating impacts in 1999, NOAA created a partnership with the U.S. Geological Survey and state officials to develop 16 map libraries for the Tar River Basin in eastern North Carolina . Hurricanes Katrina and Rita (2005) exposed the vulnerability of other coastal states to inland flooding caused by tropical storms. Thus, the concept was expanded to the Gulf region. The NWS is in the process of creating a total of 35 flood inundation map libraries for locations in Texas , Louisiana , Mississippi , and Alabama . The majority of these new map libraries will be available before the mid-point of the 2008 hurricane season.

“The NWS has conducted extensive outreach with our diverse user community to validate the need for flood inundation map libraries,” stated Dr. Thomas Graziano, Chief of the NWS' Hydrologic Services Branch.  “For only a small incremental investment beyond the cost of a typical FEMA Flood Insurance Study, state and local communities can produce inundation libraries which provide the capacity to make more informed strategic and tactical decisions to better plan for and mitigate the impacts of floods.” 

NOAA is vigorously building coalitions with additional emergency and floodplain managers to implement this new, cost effective hazard visualization and communication technique for other vulnerable flood-prone areas. Leveraging the investments being made by the Lower Colorado River Authority and the Susquehanna River Basin Commission, NOAA plans to fast-track the implementation of flood libraries for NWS river forecast locations in these areas.

The National Flood Insurance Program's (NFIP) Community Rating System (CRS) is a voluntary incentive program that recognizes and encourages community floodplain management activities that exceed the minimum NFIP requirements. As a result, flood insurance premium rates are discounted to reflect the reduced flood risk resulting from the community actions meeting the three goals of the CRS:

1. Reduce flood losses
2. Facilitate accurate insurance rating
3. Promote the awareness of flood insurance.

“Communities which make the investment and partner with the NWS to implement flood inundation map libraries can receive discounts in their flood insurance rates through the National Flood Insurance Program,” stated Berry Williams, of Barry Williams and Associates Inc, who has worked over the years with FEMA to create and update FEMA's CRS Schedule of credited activities identified to help reduce insurance costs.

It is important to know when a flood will occur, how bad it will be, and how long it will last. AHPS ability to provide a map showing people the areas for potential flooding will more clearly identify places where people and property owners need to take action. Anyone who may someday be impacted by flooding will benefit from these new inundation maps. Community leaders interested in the creation of inundation libraries are encouraged to coordinate with their local NWS office or communicate their interest via the feedback page accessible through http://www.weather.gov/ahps/.