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New mapping reveals hidden flood risks

Climate Risk and Resilience

December 17, 2020

Recent comprehensive U.S. flood risk data suggests a far greater flood risk in most places than FEMA suggests.

On June 29, 2020, a nonprofit research and technology group, First Street Foundation, released flood risk data for more than 142 million homes and other properties across the U.S. that suggests a far greater flood risk in most places than current FEMA/NFIP mapping.1 FEMA stated it welcomed First Street’s initiative and that it would be used to complement FEMA’s efforts.

This new report takes into consideration sea level rise, rainfall and flooding along smaller creeks not currently mapped by FEMA. According to the new calculations by First Street, some 14.6 million properties are at risk for damage from a 100-year flood (one with a 1% chance of striking in any given year), which is considerably more than the 8.7 million estimated by the FEMA maps, representing a 70% increase. When adjusted for future environmental factors, such as changing sea levels, warming sea surfaces, atmospheric temperatures and changing rain patterns, First Street’s model finds the number of properties at substantial risk of flooding, reaching 16.2 million by 2050.

Flood maps are critically important as they guide building decisions and decisions about which properties require owners to purchase some form of flood insurance. Mortgage lenders are particularly interested in accurate flood maps because they guide them in terms of the risk they undertake when making loans. The fact that current federal flood maps are considerably out of date means important financial decisions have been and continue to be made based on inaccurate information. The consequences are considerable.

First Street’s model was developed by more than 80 hydrologists, researchers and data scientists representing some of the top universities in the country and is based on decades of peer-reviewed research. Based on this research, supplemented by data from FEMA, USGS and NOAA, the report produced the country’s first publicly available comprehensive flood risk model. As a part of its report, First Street’s website allows property owners to check their property to see if it is situated in the 100-year flood zone or not.2

FEMA flood maps have long been thought to be inaccurate.3 In some areas, FEMA has not done any mapping and in others, its mapping is over decades old. However, every attempt by FEMA to update its mapping for flood insurance purposes has been met with strong objections. Homeowners and public officials do not want property owners in their geographic areas to be charged the much higher flood insurance premiums that would be necessary to cover the new risks if accurate flood mapping were available. Mapping such as that needed to update FEMA’s maps is costly and labor intensive, but the biggest obstacle to updating them is fear of higher costs for flood insurance and the fact that many more property owners may well be required to purchase flood insurance based on updated map results. The former head of the NFIP until 2018, Roy Wright, suggests that since there is no way for property owners to fight higher flood insurance rates, then they fight the maps. According to Mr. Wright, “It turns into house-by-house combat.”4

Many of the results of the First Street report were startling. For example, many inland areas, including large parts of Appalachia and several major cities, saw significant increases in the number of flood-prone properties according to these maps. In both Chattanooga, TN and Charleston, W.VA., FEMA maps show well under 10% of the properties in floodplains. First Street maps suggests the percentage to be 33% or greater.

Many large cities’ maps show tens of thousands of properties at risk for flooding not shown currently on government maps. Chicago tops the list. There, current FEMA maps show only 0.3% of that city’s more than 600,000 properties inside the 100-year flood zone. First Street mapping reveals that almost 13% of city properties face that risk, 75,000 more than FEMA maps show. Adding to concerns about the new mapping results is the fact that the increased hidden risks are located predominantly near Chicago’s south side where 95% of the city’s African American population resides. FEMA maps show none of these properties within the 100-year flood zone, but First Street maps indicate that 1/3 of such properties are at risk. The disparity is consistent according to the First Street maps. In more than 2/3 of the states in the country, areas with more minority residents had a far greater share of unmapped flood risks than the statewide averages.

In terms of shoreline mapping, with the exception of areas along the Mississippi River and the Gulf Coast, where more government mapping studies have been conducted, First Street mapping shows a wide gap between FEMA maps and theirs. In Fort Lauderdale, for example, FEMA maps show 41% of the city within the 100-year flood zone. First Street maps indicate the number is closer to 2/3 of the properties, or about 13,000 more properties. Again, as in Chicago, the areas of Fort Lauderdale with deficiencies appear to be those with the greatest minority populations. FEMA indicated it is in the process of updating Fort Lauderdale’s mapping, but already there is a plan to fight the results due to concerns about more properties requiring the purchase of flood insurance.5

FEMA mapping is a critical problem facing the country as so many important decisions are made based on it by homeowners when making purchase decisions, by mortgage companies making lending decisions and by the federal government deciding how best to fund the NFIP for real risks. If FEMA does not start relying more on the comprehensive mapping work of groups like First Street or performing comprehensive remapping itself, the country will face disaster-relief financial disasters on an increasing basis.


Willis Towers Watson hopes you found the general information provided in this publication informative and helpful. The information contained herein is not intended to constitute legal or other professional advice and should not be relied upon in lieu of consultation with your own legal advisors. In the event you would like more information regarding your insurance coverage, please do not hesitate to reach out to us. In North America, Willis Towers Watson offers insurance products through licensed subsidiaries of Willis North America Inc., including Willis Towers Watson Northeast Inc. (in the United States) and Willis Canada, Inc.







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