South Florida tidal floods could occur 10 times per year by 2040


Each fall’s highest king tide, a sunny-day flood of brackish Intracoastal water that overtakes aging sea walls and gurgles up through South Florida storm drains, could occur upwards of five times each year by 2030 as seas swell with climate change.

By 2040, South Florida’s streets could experience significant tidal flooding 10 times per year, according to a new study published this month by the American Meteorological Society.

Check The Palm Beach Post’s storm tracking map.

The study, titled “In Tide’s Way: Southeast Florida’s September 2015 Sunny-Day Flood,” was released as part of a package of peer-reviewed research papers that examined global extreme weather events and their relation to climate change. It is the fifth report of its kind.

“After five years of the report, we’re seeing mounting evidence that climate change is making heat waves more extreme in many regions of the world,” said Stephanie Herring, a scientist with the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information. “As we get better at distinguishing the influence of climate change from natural variability, the local significance and impacts of this global phenomenon are becoming clearer.”

While some events researched in the report, such as 2015’s unusually cold winter in the Northeast U.S., were not linked to man-made climate change, others, such as Alaskan wildfires, record-low Arctic sea ice measurements and South Florida’s tidal floods were found to be tied to a changing climate.

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William Sweet, a NOAA oceanographer and lead author of the tidal flooding report, said the probabilities of a flooding event such as the one in September 2015 have increased 500 percent in South Florida since 1994 when measurements began at Virginia Key.

“These tide gauges are unbiased observers in time that tell us what the ocean levels have been doing. They have no agenda,” Sweet said. “We don’t know exactly what will happen in the future, but the data speaks for itself about past trends and patterns.”

Sweet said the Sept. 27, 2015, tidal flooding in South Florida was the sixth-highest flood event measured over a 20-year period. The five higher events occurred during hurricanes, including 2005’s Hurricane Wilma. While tidal flooding usually occurs September through November, Sweet’s research focused on the Sept. 27 date. So when he estimates that could repeat itself 10 times per year, he means at the extreme Sept. 27 level of nearly two feet above the mean high water level.

For Iris Frohman, the tidal flooding events mean putting sandbags at her front door and her furniture up on blocks.

Frohman lives in Delray Beach on Marine Way — a street that fronts the Intracoastal and is notorious for flooding during higher-than-normal tides.

“Last month it made it into the foyer and we were bucketing out water,” Frohman said in a November interview with The Post. “I have my upholstered dining room chairs up on my table and my furniture on railroad ties.”

Watch time-lapse of high tide flooding in Delray Beach.

Part of Sweet’s study included parsing out the impact the supermoon had on the 2015 flooding. The moon, which was in perigee and pulling extra hard on the tides, was blamed for exacerbating the flooding.

But Sweet said the so-called supermoon explained less than half of the water level rise.

“It was important, but it wasn’t the whole story,” he said.

The American Meteorological Society report was released the same day, Dec. 15, as a World Resources Institute paper on how local, state and federal governments can help create and retrofit communities so they are more resilient to climate change impacts. According to the paper, coastal flooding in the contiguous U.S. has increased between 300 and 925 percent since the 1960s.

It suggests increasing incentives for communities planning resilience measures – such as raising sidewalks – improving coordination between federal and state agencies, and requiring new infrastructure and building projects include climate-related risks.

Coral Gables Mayor Jim Cason, who participated in a media call about the World Resources Institute report, said there are areas in his city that people will have to “retreat from” as sea levels rise.

“We have $15 billion worth of property in our community where elevations are from 0 to 4 feet,” Cason said. “Our most affluent communities are along the water and at some point they may have to make a decision on whether they are going to move out, and we will have to decide whether we are going to continue to provide services.”

Cason, a Republican, said while President-elect Donald Trump may question man’s contribution to climate change, some cities are already struggling to deal with the impacts.

“We are hopeful that in this environment reasonable voices, combined with the facts on the ground, will come together to protect our communities,” Cason said.

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