12 july 2017

Scores of U.S. Communities Face Frequent Flooding in 18 Years

More than 90 locales, mostly in rural Louisiana and Maryland, already face chronic inundation

By Adam Aton, E&E News, via Scientific American on July 12, 2017

More and more visitors are traveling to Miami Beach to see how the poster child for sunny-day flooding is grappling with climate change adaptation.

Visiting elected officials ask about funding for projects related to saltwater intrusion and rising seas. They tour the central sewer treatment plant on a barrier island that's undergoing a multimillion-dollar upgrade. And if there's a king tide, they have to pull their boots on, said James Murley, Miami-Dade County's chief resilience officer.

“When you start talking about 2100, it is very tough for them to say, 'I'm making this decision for my great-great-great grandchildren,'” he said. “It's just tough to picture for people.”

Now, that picture might come into sharper focus.

For the first time, researchers have compiled an analysis of chronic flooding for oceanfront communities in the Lower 48 states. The study by the Union of Concerned Scientists, published today in Elementa, projects when flooding will become so drastic and frequent that communities will need expensive fortifications — or mass relocations.

The researchers have created an interactive tool to follow their projections.

They consider inundation to have become unmanageable when at least 10 percent of a community's non-wetland area floods at least 26 times a year — the equivalent of a flood every other week.

More than 90 communities, mostly in rural Louisiana and Maryland, already face chronic inundation. Subsidence is an issue in both states.

Miami Beach hasn't hit that threshold yet. But it faces future chronic inundation under the report's most conservative climate change projections, along with New Orleans and Savannah, Ga.

That scenario assumes global warming stays under 2 degrees, as the Paris climate agreement calls for. The picture becomes bleaker in the intermediate scenario, which assumes carbon emissions peak around midcentury and global sea levels rise about 4 feet.

That scenario leads to about 170 communities facing chronic flooding by 2035, rising to 270 by 2060, according to the report.

“Outside of Louisiana, just a few Gulf Coast communities are projected to face disruptive flooding before 2060. But by 2060, six new communities along the northern coast of Texas and six along Florida's Gulf Coast would be chronically inundated,” the paper says.

The “high scenario” — which the researchers warn is becoming more likely — assumes emissions rise through the end of the century, leading to about 6 ½ feet of sea-level rise.

That would chronically flood about 670 communities, including roughly 60 percent of all oceanfront communities on the East and Gulf coasts, according to the researchers.


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