FEMA Flood Map Accuracy

FEMA is completing $1 billion 5-year program to modernize its flood insurance rate maps and convert them to digital form. At the request of FEMA, the National Academies of Science and Engineering have established a Committee on FEMA Flood Maps to review the accuracy of these maps and to recommend cost-effective improvements to them. The Committee's report "Mapping the Zone: Improving Flood Map Accuracy" was released in January 2009. The Committee examined the relative effects of accuracy of hydrologic, hydraulic and terrain information on riverine flood maps, the factors affecting the accuracy of coastal flood mapping, and the costs and benefits of various levels of detail of flood mapping and modeling, using case studies set in North Carolina. This paper focuses on the riverine flood map accuracy portion of the report, and concludes that accuracy of the terrain data is the most important factor influencing riverine flood map accuracy.