ST. PETERSBURG — Sunny day flooding could go from an occasional nuisance to a regular problem in the city, according to a new study. It projects that St. Petersburg might see inundation at high tide more than 60 times a year in the coming decades.
Sea level rise, periodic shifts in tides and weather patterns are to blame, researchers said.
“The reason we’re worrying about it now is this has been going on forever, but we never noticed it before,” said University of South Florida College of Marine Science Associate Dean Gary Mitchum, one of seven authors on the study. “Now the high tide increase every decade or two is superimposed on sea level rise, and the combination of the two is giving us vastly increased events.”
The area could reach what the report deems a tipping point in 2033. In the decade before then, the researchers suggest, St. Petersburg will see high-tide flooding about 6 days a year. In the decade after, that number could reach 67 days of tidal flooding in one year.
This type of inundation is not catastrophic, like the impact of storm surge from a tropical storm or hurricane. It is a persistent nuisance that already soaks streets and bubbles through drains in some Florida cities, most notoriously Miami and in the Keys.
Residents of flood-prone coastal neighborhoods, like St. Petersburg’s Shore Acres, may see several inches of water on roads, forcing them to re-route drives to work, school or home — even on days when it doesn’t rain. City infrastructure, like pipes and pavement, would be submerged more often in corrosive saltwater.
The dramatic rise in flooding stems in part from a roughly 18-year tidal cycle, determined by the alignment of the sun, earth and moon, Mitchum said. This predictable pattern, he said, leads to spikes and drops in the maximum height of tides. The cycle is about to see years of declining tides, which Mitchum said will offset or mask the effects of sea level rise.
In 2033, the cycle is expected to turn around. Heightened tides in conjunction with sea level rise could create a compound effect that Mitchum said will offer a glimpse of how flooding decades into the future may reshape the region because of rising seas alone.
The lead author of the study, Philip Thompson, director of the University of Hawaiʻi’s Sea Level Center, said St. Petersburg is especially affected by the tidal changes across decades because it generally has one high tide per day, compared to other regions that experience two.
Nuisance flooding is already a worry for local planners. Pinellas County is studying the prospect of future floods in a vulnerability assessment paid for using money dispersed after the 2010 Deepwater Horizon oil spill. Local engineers in some cities are installing valves to stop the sea from filling stormwater systems at high tide.
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“It just leads to constant environmental degradation of systems — mechanical, electrical, infrastructure,” said Pinellas Sustainability and Resiliency Coordinator Hank Hodde. He recalled a meeting where he heard a resident of the Florida Keys ask local leaders to install a car wash for cleaning off vehicles exposed to saltwater flooding.
“It’s going to be here all the time,” Hodde said. “Like rain.”
A lot of research and writing has been dedicated to understanding nuisance flooding, said Jayantha Obeysekera, director of the Sea Level Solutions Center at Florida International University. But the latest analysis offers a window into how soon it could become a bigger problem. Obeysekera was not involved in writing the paper, though he knows the authors and his work was cited in the report.
The researchers used National Oceanic and Atmospheric Administrative flooding standards and tidal gauge data as their foundation and an intermediate projection for how far seas could rise.
“If it happens once a year, maybe people can live with it,” Obeysekera said. But as flooding becomes more regular, he said, residents “expect the communities to come up with adaptation so they don’t have to basically walk on water 5, 10 times a year.”
Knowing more precisely when and where flooding will hit at high tide would allow public works departments to prepare. In the next phase of his research, Mitchum said he wants to find a way for scientists to make those nearer term forecasts possible.
The almost 70 nuisance floods a year projected in St. Petersburg would not be spaced out evenly across months, according to the study. The flooding might instead happen in clusters, Mitchum said, with peaks depending on the season.
Eventually nearly every high tide in certain bad months could bring flooding, he said. Water levels around St. Petersburg tend to be highest when the sea is warmer in summer and early fall.
Although sunny day flooding should stay infrequent in the near term, Thompson, of the University of Hawaiʻi, said it would be a mistake for governments to be complacent in the coming years. Building better drainage systems and modifying zoning around Tampa Bay are two ways he imagines officials could look to mitigate future damage.
King tides that cause flooding across the state should be a bellwether, he said. “Florida is already sort of the epicenter.”
This story was produced in partnership with the Florida Climate Reporting Network, a multi-newsroom initiative founded by the Miami Herald, the South Florida Sun Sentinel, The Palm Beach Post, the Orlando Sentinel, WLRN Public Media and the Tampa Bay Times.