the hidden flood risk across america

In late June, nonprofit research organization, First Street Foundation publicly released flood risk data for over 142 million homes and properties across the country. Their data assigned every property in the contiguous United States a “Flood Factor,” a score from 1 to 10,  based on its risk of flooding over a thirty-year mortgage.

The First Street Foundation Flood Model identified nearly 70% more, or 14.6 million properties, within Special Flood Hazard Areas (SFHAs) than what FEMA reports. FEMA’s maps are what inform risk management decisions in the United States, meaning that nearly 6 million households and property owners have underestimated or been unaware of their current risk.

Why Does the Discrepancy Exist?

FEMA’s appraisal of flood risk relies on time-consuming local assessments of various catch basins and flood plains. Their methods tend to ignore smaller streams and tributaries, which hold less volume than larger bodies of water, but are numerous and run throughout the country. Furthermore, there are portions of the country that are simply not mapped by FEMA. Their focus on highly populated, high-risk areas is in part due to budget restrictions imposed by Congress.

First Street Foundation, on the other hand, mapped the entirety of the contiguous United States. The analysis of previously unmapped areas partly accounts for their higher estimate. Another driver is their methodology. While FEMA does not, First Street looks at precipitation flooding as an individual risk and captures that in their model.

On FEMA’s methodology, Dr. Ed Kearns, First Street Foundation’s chief data officer, remarked, “In environmental engineering, there is a concept called stationarity, which assumes that today is going to be like yesterday and tomorrow is going to be like yesterday. This concept used to work, but with a changing environment, it’s a poor assumption and no longer does. FEMA’s method assumes stationarity, First Street’s does not.”

The Future of Flood Risk

In addition to calculating current risk, the Foundation’s model also looked at future flood risks. When considering changing sea levels, warming sea surface, atmospheric temperatures, and changing precipitation patterns, the number of properties with substantial risk is expected to grow to 16.2 million by the year 2050. As is currently the case, future impact or risk is not distributed evenly throughout the country. The number of properties with flood risk will increase more in some states like Florida, Virginia, Louisiana, New Jersey, and Delaware than others.

What Next?

While this data may be off-putting to many homeowners, it allows for more informed decision-making. Individual property owners can take action to mitigate their risk by purchasing flood insurance, seeking alternative properties with lower risk, or by modifying their properties to better withstand flooding.

By arming individuals, governments, and enterprises with this information, they are able to take more informed action to protect Americans’ most valuable asset: their homes.