Shared from the 2016-04-06 The Miami Herald eEdition

MIAMI BEACH

Flooding spiked over last decade, study finds

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If it seems like flooding in Miami Beach has gotten a lot worse a lot faster, it has.

A new study from the University of Miami found that since 2006, flooding in Miami Beach has soared — 400 percent from high tides and 33 percent from rain. The increased flooding, calculated from insurance claims, media reports and tidal gauges, stems from a regional rise in sea levels well above global increases and serves as a warning that future sea rise will likely happen in different amounts at different rates around the planet.

“I was completely shocked when I found it was rising so fast,” lead author and University of Miami geophysicist Shimon Wdowinski said of the study published this week in the journal Ocean & Coastal Management.

From 1998 to 2006, tidal gauges in South Florida show sea rise keeping up with global averages of about .04 to .20 inches a year. But in 2006, local sea rise suddenly underwent a rapid acceleration, researchers found, averaging about .20 inches to a half inch per year. While the numbers may seem minuscule, they can cause exponential changes in flooding during high tides or South Florida’s soggy rainy season that Wdowinski said could make a big difference in how planners prepare.

“They can’t assume that everything behaves the same everywhere,” he said.

Florida has come under increasing scrutiny as a string of studies paint dire pictures of the state’s future under climate-change scenarios.

Last month, researchers from Stetson University and the University of Georgia found that the state will have the most population at risk under worst-case projections of a 6-foot rise in sea level by 2100. The state also ranked first in a 2015 national survey of property under threat of flooding, with an astounding $152 billion by 2050.

While previous studies have documented the region’s increased flooding from tides, Wdowinksi said the team also wanted to examine flooding from rain because “people who live in the area know we get a lot of flooding from rain and all these rain events aren’t accounted for.”

Previous research has found that sea rise generally began accelerating on the Atlantic coast about 2000. Researchers say the increase is likely tied to a weakening in a major current — the hard-to-remember Atlantic Meridional Overturning Circulation — that carries heat from the tropics to the North Atlantic.

The influential International Panel on Climate Change forecasts it to weaken by 25 percent by mid-century.

But when Wdowinski looked at tidal records from Virginia Key, he found that seas in South Florida didn’t start rising until 2006, confirming a similar finding in 2015. So why the difference?

One theory could be Florida’s fast-moving Gulf Stream. When it’s strong, the current pulls water into it, building a ridge of water. When it’s weak, the water flows back toward shore. Some researchers have suggested that Greenland’s melting polar ice sheets have dumped so much freshwater into the ocean that it is diluting heavier saltwater that normally sinks and keeps the current moving. But Wdowinski said that so far no consistent decrease has been detected.

And Florida is not alone in experiencing different rates of sea rise. Other regions have also experienced changes at different rates — warming oceans caused seas to rise in between Japan and Korea from 1993 to 2001, and surface winds have increased levels in the Indian Ocean since the 1960s. The western Pacific has risen nearly eight tenths of an inch higher than the global average, Wdowinski wrote.

That means defining what drives sea rise in a given area is probably more complicated and involves a variety of factors including local changes in salinity, difference in ocean warming, changes in currents and circulation, and ice melt. The last decade of rapid acceleration could also mean South Florida is in for more sea rise than global projections, meaning engineers designing solutions may want to pay more careful attention to local predictions.

“If local rates of sea-level rise are significantly higher” than global averages, researchers warned, pumps, road-raising and other solutions now being drafted will likely provide “protection for a shorter time period than planned.”

Follow Jenny Staletovich on Twitter @jenstaletovich

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