Coastal communities should exercise caution in using FEMA Flood Maps as the primary indicator of coastal risk.

The new, draft flood maps are out for Mexico Beach, FL. First, please understand the following. We know that FEMA's flood maps are constructed differently from something like NOAA's SLOSH Maximum of the Maximum Envelope of High Water (MEOW), or (MOM) which predicts the degree of storm surge flooding during the "perfect storm" along a particular shoreline. We also understand that FEMA's flood maps are created primarily to establish flood insurance rates and to assist communities in reducing those flood insurance costs through the community rating system. These products were not developed to provide a comprehensive accounting of the coastal hazards facing any community or any individual parcel of land.

But here's the problem, almost no one else understands this. Most coastal communities, like Mexico Beach, rely almost entirely on FEMA flood maps to understand their exposure to coastal hazards and risk to the community. The map above shows properties in Mexico Beach that were destroyed or heavily damaged during hurricane Michael and are located in the X-Zone of the new, preliminary Flood Maps. These properties would not be required to purchase flood insurance (although they still can voluntarily) and they have no mapped Base Flood Elevation (BFE). Are they exposed to flooding? That is not a difficult question to answer. During Michael, the area of this X-Zone had water at 4-5 feet above ground level and most of the homes were destroyed.

Fortunately, town leaders in Mexico Beach recognize the exposure of their community (how can they not) and have enacted an ordinance that goes well beyond what most other coastal municipalities have done. They will require future construction to include 1.5 feet of freeboard above the X (0.2 %) flood level (roughly 500-year flood plain). If there are other oceanfront communities that have adopted such forward-looking regulation, we are not aware of them. Most communities typically require elevation of only those properties in the "high-hazard" VE and AE Zones. FEMA establishes a BFE in these areas that approximates water level in a 100-year flood (1 %). This approach in Mexico Beach would have left most of the community unprotected after rebuilding. This new ordinance will require some properties to elevate 6-8 feet above the FEMA BFE in A-Zones and more importantly, includes regulation of the X-Zone.

FEMA's X-Zone, which most communities do not regulate, clearly underestimates the hazard (again, see the map above). Even with Mexico beach's new ordinance, most of newly constructed properties will still be below the actual, measured, water heights for hurricane Michael, but just barely. The ordinance sets an important precedent that other municipalities should consider. Mexico Beach got it right.

Just imagine though if they did not have hurricane Michael to guide their decision making. These new FEMA Flood Maps would suggest that Mexico beach need only to actively manage a thin sliver of their coastal properties, and that a significant portion of the community might not even be required by a lender to carry flood insurance (there is some variability in this). We are baffled that many parcels destroyed during Michael were removed from the AE-Zone and placed into the lower hazard X-Zone (see the figure below). These changes show some important limitations of the FEMA maps.

They seem to be accounting for subtle changes in elevation (maybe they got a better DEM) without considering the geomorphic setting. The same thing happened with the new maps proposed for Dare County, NC. Some houses on the oceanfront went from A to X because they were sitting on an oceanfront dune, even though shoreline erosion would drop that house into the ocean in less than 10 years. We know that FEMA began working on these proposed maps before Michael, and the elevation data utilized was clearly pre-storm (everything was flattened post-storm). But, we just can't get past the fact that the majority of this community remains in an X-Zone when Michael just showed us the true exposure.

FEMA has a difficult, and politically fraught job in making Flood Maps. It is not our intent to chastise those who are working hard to complete a daunting task. We like the new parcel-level inspector developed by the Northwest Florida Water Management District that allows one to look at X-level flood projections and even field measurements of water levels from Michael (https://portal.nwfwmdfloodmaps.com/esri-viewer/map.aspx?cty=MexicoBeach). There is good information in there. Honestly, lots of people don't like recognizing the exposure of their property to flooding and storms. Many communities ask for reductions in the high-hazard areas because their constituents don't want to spend the money to elevate their properties. Still, in our opinion, the product in its typical application underestimates the risk.

Perhaps the real lessons to be learned here are for communities other than Mexico Beach— those communities with unregulated X-Zones. Just consider how much exposure and vulnerability you must be missing if your ordinances and town planning only consider the VE and AE Zones. Mexico beach learned that lesson the hard way. You have a chance to make some changes in advance of the next storm.

Published with assistance from Katie Peek and Blair Tormey. Contact Rob Young at [email protected]