If you own a waterfront property and your FEMA flood map shows low risk, you might feel like you have nothing to worry about. That feeling could be one heavy rainstorm away from costing you everything, according to Albert Slap, founder of RiskFootprint™, who has spent more than a decade working with property owners, lenders, and due diligence professionals on natural hazard risk.
Slap’s message to waterfront property owners who rely on FEMA flood maps alone is direct: the map is not telling you the full story. “FEMA flood maps don’t include heavy rainfall flooding,” Slap says. “Wherever it rains, it can flood. That’s the part most property owners never hear until it’s too late.”
FEMA flood maps were built around a specific type of flood risk: riverine flooding, meaning rivers and streams overflowing their banks, and coastal surge from major storm events. They do not model rainfall-driven, or pluvial, flooding—the kind that happens when a storm dumps several inches of rain in a short period and drainage systems cannot keep up. For waterfront property owners, this distinction is critical. A property on a bay, canal, or lake may show up as low risk on a FEMA map, but the map says nothing about what happens when three inches of rain falls in two hours. FEMA maps also have an age problem; many were drawn decades ago and have not been updated for changes in development or rainfall patterns.
The consequences of misplaced confidence in FEMA flood maps played out during Hurricane Harvey in 2017. Approximately 150,000 homes in the Houston area flooded, and 70% were in FEMA’s X Zone, the designation for lower flood risk. Most of those homeowners had no flood insurance because the map told them they did not need it. Harvey caused an estimated $125 billion in total damages. The flooding was caused by rainfall, not rivers overflowing.
A flood assessment that reflects the full risk picture must integrate rainfall-driven and other flood modeling alongside FEMA maps, including models from NOAA, NASA, and sources like RiskFootprint™, which uses flood models from Fathom and Swiss Re to cover riverine, coastal, and pluvial flooding. But flood exposure is only part of the picture. The other critical factor is a property’s vulnerability, which depends heavily on how high the first floor sits above the ground. Using AI and machine learning applied to Google Street View, RiskFootprint™ estimates first-floor elevation across more than 300 million U.S. properties.
Slap offers practical guidance: Do not treat a low FEMA X Zone as a clean bill of health; check whether you have flood insurance regardless of your FEMA zone; and get a property-level hazard assessment before buying, selling, or refinancing. A complete flood risk assessment for any U.S. residential property is available for $200 at riskfootprint.com/residential-product. Knowing your actual exposure across all flood types is becoming an expectation in some states.
