U.S. More at Risk for Devastating Floods Than Originally Thought

The next time you read flood predictions for your area, don’t be so confident that they’re accurate. Traditional flood analysis techniques may have actually underestimated flood risk for many areas across the U.S., a new report has found.

According to Time, scientists, engineers and disaster experts have typically determined flood risk by examining storm surges and high rainfall separately.

New research, published in the journal Nature Climate Change, has found that this method fails to account for the risk of storm surges and high rainfall taking place in tandem. These “compound events” have become more commonplace over the last century, thanks to the increasing effects of climate change.

In New York City, for example, a re-evaluation of flood risk that also accounts for compound events found that the city’s odds of flooding are more than double those that were previously determined. Places like Boston, Tampa, FL, Houston, San Diego, Los Angeles and San Francisco are also at risk for devastating floods caused by compound events.

“Usually it requires an extreme storm surge to cause flooding or an extreme rainfall event,” said study author Thomas Wahl, a researcher at the University of South Florida. “But the combination of two events that are not really extreme on their own may cause larger damages than one of the two events alone.”

Currently, floods are the No. 1 disaster in America, the National Flood Insurance Program reports, bringing in more than $3 billion in damage claims annually. While the risk for compound events varies widely on a city-to-city basis, cities prone to experiencing hurricanes across the East and Gulf coasts are generally more prone to compound events than cities on the West coast.

Despite these troubling findings, the researchers maintained that compound events are, in comparison, the least of the country’s worries — as long-term sea level rise continues to be the biggest driver of increased flood risk.

The latest estimates, released a week before the University of South Florida study, claim that global sea levels could rise 10 feet above their current levels within the next 100 years. If these estimates are accurate, that would mean cities like New York City and London could become uninhabitable within decades.

“Continued high emissions would result in multi-meter sea level rise this century and lock in continued ice sheet disintegration such that building cities or rebuilding cities on coast lines would become foolish,” Dr. James E. Hansen, of Columbia University, wrote in a statement accompanying his paper.