Millions More American Homes Are at Risk of Flooding Than Previously Known, New Analysis

06/29/2020 Science


Today, about 8.7 million properties are located in special flood hazard areas as determined by FEMA Flood Maps, the legal standard used in the US to manage flood plains, determine insurance requirements and premium pricing policies.

But up to 14.6 million properties, nearly 70% more than FEMA’s Special Flood Hazard Areas, may actually be at significant flood risk, according to the First Street model. The discrepancy between FEMA maps and this new information means that some 6 million homeowners may be unaware of their current flood risk, the group says.

“If you are an owner, tenant, or buyer in this country and want to understand flood risk, the only data available is FEMA flood maps,” said Matthew Eby, founder and CEO of First Street. “And FEMA’s flood maps are made to determine flood insurance rates, not necessarily to determine what your personal flood risk is.”
As climate change raises sea levels and leads to more extreme rainfall events, even more homeowners will have to deal with the threat of flooding, within the life of a 30-year mortgage signed today.

First Street found that by 2050, the number of properties with significant flood risk is expected to further increase to 16.2 million.

The problem is already growing urgently, as large areas of the country have been flooded by devastating floods in recent years.

Flooding is now the most common and costly natural disaster in the US, causing property damage of about $ 155 billion in the past decade, according to Michael Grimm, assistant administrator for risk management at the Federal Administration for Insurance and Mitigation, who testified before the Science Committee Chamber in February.
Last year, many parts of the Midwest and South were inundated by floods that lasted for months and caused $ 6.2 billion in damage and four deaths, according to NOAA.
In 2017, Hurricane Harvey, a powerful Category 4 storm, shed a record 51-inch rain in parts of Texas, putting large parts of Houston underwater. But about half of the flood-affected houses in Houston were outside of the mapped floodplains, according to a report by the National Academy of Sciences on urban flooding.

Right now, First Street flood models show that the states with the highest proportion of properties currently at substantial risk are West Virginia, Louisiana, Florida, Idaho, and Montana.

In the future, changes in precipitation patterns will continue to cause problems for many towns and cities in the interior.

But as the climate changes, the combined threats of storm surges caused by hurricanes and rising sea levels mean that flooding will be more dramatic in coastal areas, according to First Street.

By 2050, almost 98% of properties in New Orleans could be at substantial flood risk. Under the First Street model, South Florida will also see big impacts, with Miami and Tampa projected to see more than half of all properties at risk of flooding by 2050.
However, FEMA’s flood maps do not take into account the effects of climate change, a reality that Grimm seemed to recognize in his House testimony, saying there is “a lack of consideration for future weather patterns and changing coastal conditions. “on current maps.

Other deficiencies in FEMA’s flood maps have long been recognized, including by the agency itself.

During his testimony in the House, Grimm said that FEMA has not yet completed flood maps for large areas of the United States.
And while Congress requires that FEMA maps be reevaluated every five years, Grimm says it takes an average of seven years to complete a new flood map, which means some maps may be technically outdated by the time they are done.
Floods surround a farm in March 2019 near Craig, Missouri. Last year, the Midwest states battled some of the worst flooding the region has seen in decades.

In an email response addressing the First Street findings, David Maurstad, FEMA Deputy Assistant Administrator for Insurance and Mitigation, said: “FEMA is constantly working to improve the production of Flood Insurance Rate Maps in context. of changing conditions. “

Still, these new data shed light on the growing climate risk millions of Americans already face, though many may be in the dark about their personal exposure, experts say.

“This is more evidence showing that our mapping system is not working efficiently and we need to fix it to better understand flooding in the United States,” said Dr. Hamed Moftakhari, an assistant professor at the University of Alabama, who studies threats that natural hazards pose to coastal communities.

In addition to its report, First Street is also launching a new interactive modeling system called “Flood Factor,” which will allow prospective homebuyers to explore current and future flood risk for any property on or off the market in the States. United contiguous.

The tool assigns a Flood Factor score between 1-10, with one being the lowest risk and 10 being the highest, and allows users to explore how a property’s flood risk is projected to change in the coming decades.

“Sophisticated investors have bought private flood risk information from for-profit companies for years,” Eby said in a press release. “Not only has the First Street Foundation taken this type of data to the next level, using peer-reviewed science, but it is correcting an information asymmetry by providing free access to ordinary Americans.”

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