Extreme flooding occurs more often than federal estimates: report

A new analysis has revealed that current federal data on extreme precipitation severely underestimates the likelihood of flooding.

According to findings published by the nonprofit First Street Foundation, the US government’s rainfall frequency estimates do not adequately capture the frequency and severity of extreme precipitation in the face of climate change.

As such, events classified as a “1 in 100 year flood” occur more frequently than anticipated.

In fact, First Street Peer-Reviewed Model found that about 51% of Americans reside in areas that are twice as likely to experience a 1-in-100-year flood compared to predictions from Atlas 14, the rainfall frequency estimates widely used by the National Oceanic Administration and Atmospheric (NOAA) .

Jeremy Porter, First Street’s head of weather implications, said the discrepancy is due to infrequent updates to Atlas 14, which has not kept pace with intensifying rainfall events caused by the climate crisis.

Extreme floods and the impact of climate change

The First Street study revealed that about 21% of the country can expect a 1-in-100-year flood to occur every 25 years.

Meanwhile, more than 1.3 million people in 20 counties, including parts of Indiana, Kentucky, Pennsylvania and North Carolina, may experience these extreme flooding at least once every eight to 10 years.

“The magnitude of the changes in expected rainfall intensity is alarming for many areas in the United States,” said Jungho Kim, First Street senior hydrologist and lead author of the study. “And it’s important that Americans are fully aware of this consequence of climate change that can affect their lives and homes.”

The research also shed light on regions such as the Northeast, the Ohio River Basin, northwestern California, the Texas Gulf Coast and the Mountainous West, where rainfall for a 1-in-100-year event could occur at least every five years. to 10 years. .

In addition, he highlighted the impact of climate change on densely populated cities. One example is Houston, Texas, where the probability of a 1-in-100-year flood event has increased by 335% since Atlas 14, making it a 1-in-23-year event.

Another concern raised by First Street is the recent allocation of $1.2 trillion through the Infrastructure Investment and Jobs Act (IIJA) for capital investment and infrastructure spending through 2027.

Since many of these projects will require engineering expertise to withstand weather-related risks, including precise flood design standards, the group said the estimates in NOAA’s Atlas 14 could lead to billions of dollars being spent. dollars on projects that may not stand the test of time.

“The fact that the nation did not have the most accurate estimates of extreme precipitation probabilities available at the time these projects were designed means that many of them will be out of date by the day they open to the public,” Matthew said. Eby, founder and CEO of the First Street Foundation.

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