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Here’s What Tampa Bay Can Expect From New Sea Level Rise Projections

Florida’s near-future of higher sea levels and more flooding is coming into sharper focus, according to a new government report, even as scientists say worst-case conditions appear to be further off than initially thought — giving people additional time to prepare.

Across the United States, sea levels are expected to jump 10 to 12 inches in the next three decades — about the same rise that took place over the last 100 years, according to researchers at several federal agencies and universities, led by the National Oceanic and Atmospheric Administration. Damaging floods could happen 10 times as often, scientists say.

In Tampa Bay, a regional advisory panel has recommended local governments plan for a range of sea level rise between roughly 11 and 31 inches from 2000 and 2050, based on a similar federal study from five years ago. The new projections, announced Tuesday, would raise the low end of that spectrum to just over a foot and drop the high end to about 19 inches in St. Petersburg.

“It’s a shift in the timing, not so much in the height,” said Gary Mitchum, associate dean at the University of South Florida College of Marine Science, who served as a reviewer for the federal report. Mitchum is a member of the regional science advisory panel, which he said will assess the data and revise its guidelines as needed.

Though the latest study lops off a previous “extreme” projection for sea level rise over the next few decades, Mitchum said people could still face similar conditions after 2100. He said Floridians should think of the estimates like a “cone of uncertainty” for approaching hurricanes.

“We’ve taken that cone, and we’ve narrowed it down,” he said. “There’s still going to be a hurricane. There are still going to be impacts. But we have a much better idea now of what they are.”

Sea level rise has accelerated across the world, spurred by global warming. People burn fossil fuels, releasing greenhouse gasses that heat the atmosphere. Warm temperatures cause water to expand and ice sheets to melt. Scientists say earth is locked into more heating and sea level rise, but people can stave off the worst consequences of climate change by lowering emissions.

Water pools on W. Maritana Drive in St. Pete Beach where work on drainage improvements was ongoing last fall. [ DOUGLAS R. CLIFFORD | Times ]

Compared to past research, the new report frames discussions more around a 30-year window, relatable to people as the length of a standard mortgage. Richard Spinrad, who leads the National Oceanic and Atmospheric Administration, called it “a wake-up call for the United States.”

Nicole LeBoeuf, director of the National Ocean Service, said she grew up on the Texas coast and knows how shorelines shift naturally. But the problems mounting before cities today are different.

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“These are not the kind of changes we grew up with,” LeBoeuf said. “Make no mistake: Sea level rise is upon us.”

South Florida, and especially Miami, is already a prominent example for sunny-day flooding, which fills streets with seawater during peak tides. That phenomenon will migrate to other cities and soak waterfront neighborhoods more frequently, said Thomas Wahl, a University of Central Florida engineering professor who was a reviewer for the government report.

Meanwhile, he said, storm surges that Floridians already fear will be more devastating.

“We don’t need as big a storm surge anymore — we maybe don’t need a Category 3 hurricane making landfall, but maybe a tropical depression” to cause major flooding, Wahl said.

Tampa Bay is especially prone to destruction from surges already, a threat that a recent Tampa Bay Times special report shows will grow substantially over the next 30 years. Mitchum’s research has predicted a rise in sunny-day floods over time, too.

A few inches of saltwater intrusion is costly. Regular floods cause infrastructure like stormwater pipes to degrade more quickly and can make low-lying neighborhoods hard to reach.

Higher water doesn’t only affect people and property. It will lead to more beach erosion and the loss of coastal marshes in places like Hernando County, said Davina Passeri, a research oceanographer for the U.S. Geological Survey in St. Petersburg. The state’s natural shoreline has offered protection from flooding and waves during storms, while serving as a key habitat for animals like birds and turtles.

“Between the dunes and the marshes … we’re going to lose that natural buffer,” said Passeri, who, like Mitchum and Wahl, reviewed the federal report. She is also a member of Tampa Bay’s Climate Science Advisory Panel.

Florida’s state leaders have started to direct hundreds of millions of dollars toward flood infrastructure projects such as revamped stormwater drains and seawalls. Adapting to future flooding will cost many billions of dollars. Hardening defenses will not be enough to save everything people have already built. In some spots, including the Florida Keys, leaders are already managing a limited retreat from vulnerable properties.

In Pinellas County, the research reinforces the need for local governments to react, said Hank Hodde, the county’s sustainability and resiliency coordinator.

“I just hope this report can help fine-tune what we’re already doing and bring new people on board,” he said.

The study also highlights how quickly science is advancing while climate change becomes a more urgent, universal discussion.

Wahl remembers that when he started his career 15 years ago, “we didn’t have a name for high tide flooding.” Now everyone knows the term, if they haven’t already experienced the effects themselves.

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