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New Model: Nearly six million more U.S. homes in flood danger

Independent analysis shows greater risk than FEMA maps indicate

By Anthony SanFilippo
July 2020

Assessing the risk of a flood is a herculean undertaking. Trying to predict long-term weather patterns, the impact on the rise of water in a certain area, as well as changes in the topography of land over time from natural or man-made changes, makes identifying the risk a constant struggle.

That unenviable task falls under the purview of the Federal Emergency Management Administration (FEMA) which makes the best of limited resources to produce the highest quality maps to support community safety regulations for as much of the country as possible. Nevertheless, a recent analysis has found that by not including all sources of flooding (e.g., heavy rainfall) and being updated frequently,  the federal flood maps have underestimated the flood risk to almost six million homes or structures in the United States.

The analysis was conducted by the First Street Foundation, a non-profit that created a consortium of scientists, researchers and engineers from Rutgers University, the University of California at Berkley and George Mason University, as well as researchers from the Rhodium Group and flood analysts from Fathom. They took on the ambitious task of extending FEMA maps to every home in America except for Alaska and Hawaii.

“Significant gaps exist in California, Pennsylvania, Texas, New York, and Tennessee, mostly driven by areas that you wouldn’t think of as high flood-risk locations, like Chattanooga or Philadelphia.”

While FEMA maps are generally very expensive, labor intensive and time consuming, First Street was able to leverage advances in catastrophe modeling and remote sensing technologies – like LiDAR from airplanes – in order to overcome the mapping challenges and generate a nationwide model that measured flood assessment to high degree of accuracy and precision.

It was major step forward in educating the nation’s property owners about flood risk and protecting the U.S. taxpayer in the process.

The group’s modeling is “exactly what we need to be doing,” Kerry Emmanuel, a professor of atmospheric science at MIT who serves on First Street’s advisory board, told USA Today. “Until recently we didn’t have people putting all these little pieces together. We had really good people working on that little piece of the problem and good people working on another little corner.”

The new model identified roughly 14.6 million American homes – or about 1 of every 10 homes in the country – have an annual risk of flooding of at least one percent, which is the threshold the federal government uses to assess which homeowners are required to purchase flood insurance. This is contrary to FEMA’s list, which is about 40% lower, at 8.7 million properties in the floodplain.

First Street’s model didn’t just identify blind spots in the FEMA maps, but also made 30-year projections. According to their data, an additional 1.6 million properties will reach that one percent risk plateau by 2050.

While one percent might not seem high – it’s about the same risk you take driving 70 MPH on the highway – if you extrapolate that over the length of a 30-year mortgage on a property, the odds of a home flooding before a mortgage is paid off is about 1-in-4, or 26 percent.

Many of the largest discrepancies between FEMA and First Street maps were in states and cities not typically considered at high-risk for flooding.

Significant gaps exist in California, Pennsylvania, Texas, New York, and Tennessee, mostly driven by areas that you wouldn’t think of as high flood-risk locations, like Chattanooga or Philadelphia.

According to First Street, another big city – Chicago – has an additional 76,000 properties that should be on the FEMA floodplain, but aren’t.

And it’s not just large urban settings like Chicago where FEMA appears to underestimating homes in the floodplain. First Street identified West Virginia as the state with the greatest discrepancy and having even more homes at-risk than Louisiana or Florida.

Repeatedly Flooded Homes Also on the Rise

While First Street’s research is the most comprehensive to date, it is not the only chink the nation’s armor against flooding that was recently identified.

The U.S. Government Accountability Office (GAO) found that programs designed to move homes out of floodplains or provide fortification of homes by elevating them – or flood proofing – are not keeping pace with the number of properties with repeated flooding.

GAO found that there was a 43 percent increase in the amount of repeatedly flooded properties in the U.S. climbing from 150,000 in 2009 to 214,000 by 2018.

In a changing climate when storms appear to be intensifying and coming more frequently, the GAO expects that number to continue to rise.

Most flood experts agree that FEMA must modernize to stay ahead of the curve, especially in inland areas where urban flooding due to heavy rainfall clears the one percent line of demarcation but is not currently included on the maps.

Even with those limitations, FEMA’s methods, which were developed decades ago, assesses only riverine and storm surge flood risks using historical data and without accounting for projected sea level rise along much of the coast

According to USA Today, FEMA and local officials don’t always see eye-to-eye.

Grover Fugate, former executive director of Rhode Island’s Coastal Resources Management Council, noted that FEMA revamped its flood maps along the state’s coast a few years ago, and actually lowered storm-surge estimates by up to five feet.

Concerned that the agency was using a 50-year-old model to predict the way a storm surge would begin moving over the land, Fugate and his team created their own flood maps and found that FEMA underestimated wave heights in severe storms by as many as 16 feet.

Impact on Flood Insurance

Meanwhile, with this new data, the ever-struggling National Flood Insurance Program (NFIP) now faces another financial crisis.

The NFIP has not been able to be a self-sustaining entity ever since Hurricane Katrina in 2005, and GAO has listed the NFIP as “high-risk” and in need of a complete overhaul.

Some lawmakers have suggested that the NFIP could move back into the black by mitigating properties that have repeated flood claims either by buying them out, or through flood-proofing.

However, current mitigation efforts are not keeping up with the growth of the repetitive-loss properties and by itself, will not solve the problem.

“Mitigation alone will not be sufficient to resolve NFIP’s financial challenges,” GAO wrote in a June 2020 report. “A more comprehensive approach is necessary to address the program’s fiscal exposure.”

Combine the new data from First Street with GAO’s findings and suddenly, Congress may not have a choice but to consider allowing flood insurance premiums to rise.

The GAO report identified approximately 1 million NFIP policies with premiums that are artificially low and do not reflect the property’s actual flood risk.

GAO suggested that affordability can be addressed by bringing the hidden subsides out into the open and removing them, except for the lowest-income property owners.

“Assigning full-risk premium rates to all policies would remove subsidies from those who do not need them, helping improve solvency. It would also more accurately signal the true flood risk,” GAO wrote.

There’s an app for that

First Street has also released a tool and website called “Flood Factor.” It’s a downloadable application for a phone in which homeowners and buyers can evaluate any property’s flood risk. It also allows for a historical search on the flooding of a property.

“This sounds like a CARFAX for homes,” Larry Bartlett, the property appraiser for Volusia County, Fla. told USA Today. “If I was a lender, I’d want to know if the property I was lending money on stood a good chance of being underwater in 30 years.”

Along with USA Today, information from Climatewire was also used in this report.

Want to learn more about how to be prepared for a flood? Check out these links below:

Be Prepared for a Flood
Factsheet on how to stay safe before, during, and after a flood.

Flood Social Media Toolkit
Website with social media resources.

12 Ways to Prepare
A postcard with 12 steps you can take to be more prepared.

Document and Insure Your Property
Document outlining specific steps you can take to document and insure your valuables before a disaster.


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