Flood maps used by the Federal Emergency Management Agency (FEMA) are out-of-date and understate the risks to homes and businesses from flooding and extreme rain triggered by climate change. One study came to the same conclusion: a 2020 evaluation of flood risk by the non-profit group First Street Foundation, which analyzed every property in the 48 contiguous US states and found that federal maps underestimate the number of homes and businesses in significant danger by 67%. Now, it is also the opinion of FEMA’s Director Deanne Criswell.
During a nationally televised interview on CNN, Criswell said, “I think the part that’s really difficult right now is the fact that our flood maps don’t take into account excessive rain that comes in and we are seeing these record rainfalls that are happening.” She also stated that climate-fueled extreme weather complicates the risk, making risk hard to predict and challenging whether a city or town’s infrastructure can hold up.
“We have to start thinking about what the threats are going to be in the future as a result of climate change, but right now FEMA’s maps are really focused on riverine flooding and coastal flooding,” Criswell said.
Design risk if FEMA maps are the sole source for design information
The intended purpose of FEMA maps is for insurance rating, and not as the sole source for design information. FEMA’s Flood Insurance Rate Maps (FIRMs) that indicate the Base Flood Elevation (BFE) were initially created so the National Flood Insurance Program (NFIP) could rate buildings within a floodplain. NFIP uses the maps to compare a reference elevation, such as the elevation of the top of the lowest finished floor, to the elevations (BFEs) presented on the maps, which are based on the one-percent annual chance of a flood, also referred to as the chance of a 100-year flood.
More than 20,000 communities participate in the NFIP. The impact to design firms is that since participation in the NFIP requires a community to adopt the FIRMs in its floodplain ordinances, local building codes adopted the maps as the minimum standard that buildings must meet. The FIRMs represent the probable flood patterns at the time FEMA performed hydraulic and hydrology modeling. This puts a burden on the design team referencing the flood ratings because if a map has been updated, a designer must determine whether the map reflects new modeling or whether there was some other change that FEMA recognized and revised the map without re-running the flood modeling.
For example, a map with a 2009 date could represent modeling completed in the 1980s and provide inappropriate guidance for rating the flood risk for insurance purposes and unreliable design information. According to FEMA, the maps represent the best available data at the time the modeling was completed, but because of changes in a community over a period of 20 or 30 years, unrecognized factors could increase flood heights. Design firms also face the exposure that while the maps are intended to represent current conditions, to properly serve their clients and protect public safety, firms should think about changing flood conditions over the life of a building and design with these changes in mind.
Communicate the increased risk of flooding with the client
Remind clients that floodplain maps referenced by local ordinances, building codes, and design standards can serve as the basis for calculating the minimum required elevation, but that they are only a starting point for design. Many project owners might mistakenly regard the standard’s minimum required elevation as the required elevation. To try to avoid future claims, it is prudent for professionals to look at other factors and recommend designing above the minimum required elevation if the elevation is too low in their judgment. The principle of informed consent means that design professionals should tell their project owner that there is likely to be additional risk not accounted for in FEMA’s maps. If the project owner chooses to ignore the rationally determined and properly communicated professional advice, the decision to design to the absolute minimum should be documented.
Certifying impermeability can lead to claims
In some cases, mainly in non-residential construction, professionals can construct buildings in the regulated floodplain below the required elevation as long as the design professional designs the building to keep water out and they certify that the walls and building slab are “substantially impermeable” by meeting specific engineering requirements referenced in the floodproofing certificate published by FEMA. FEMA developed the floodproofing certification language primarily because the NFIP requires certification that a building has been flood-proofed up to a specific elevation, which is usually the BFE value plus one foot. As with all certifications on which others can detrimentally rely, the design professional should not provide such a certification without having performed the special inspections needed to determine that the contractor completed the work adequately, and charge the client appropriately for the increased level of services and risks.