Assessment of National Weather Service Categorical Flood Inundation Mapping (CatFIMs) in Preparation for their Public Release

As the National Weather Service (NWS) continues its phased rollout of dynamic flood inundation mapping (FIM) to the public, approximately 30% of the U.S. population now benefits from the availability of these FIMs. In support of the rollout, River Forecast Centers (RFCs) serving the areas where the FIMs are now public have developed training plans, conducted webinars, and provided outreach and technical support to emergency management officials and federal, state, and local partners in their regions. For the Northeast RFC (NERFC) region, the 30% FIM public release area includes the County Warning Areas (CWAs) of the New York Weather Forecast Offices (WFOs) in Albany, Binghamton, and Buffalo.

In addition to the dynamic FIM products becoming available during the rollout, other ancillary FIM products are also being produced. Some of these products are identified as static FIMs. Unlike the dynamic FIMs, which are revised with each corresponding atmospheric model update, static FIMs remain unchanged and provide users with expected inundation extents for fixed hydrologic flows or river stages. Two of the ancillary static FIM products scheduled for release along with the dynamic FIMs are the Stage-Based and Flow-Based Categorical FIMs (CatFIMs). These two products show the expected inundation extents for individual flood threshold categories (Minor, Moderate, Major, and Record flood) as well as for Action Stage.

Each RFC has been conducting technical reviews of the CatFIM products, in preparation for each phase of the dynamic FIM rollout. These assessments determine whether the CatFIMs are sufficiently accurate compared to observed impacts at each CatFIM location. Since the methodology for creating CatFIMs is similar to the process for generating dynamic FIMs, the assessments also provide users with a corresponding level of confidence regarding the expected quality of the dynamic FIMs when they are generated.

This presentation discusses the NERFC’s experiences with CatFIM reviews for the 10% and 30% phases of the FIM rollout. The methodology employed for the reviews, as well as the results, will be examined. Recommendations for future CatFIM review activities will also be provided.