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Rising Sea Levels, High Tides Will Lead To More Floods, Researchers Warn

 In October 2018, Shore Acres in St. Petersburg was flooded due to high tides.
St. Pete Police / Twitter
In October 2018, Shore Acres in St. Petersburg was flooded due to high tides.

According to a new study, high-tide flooding events are projected to increase rapidly beginning in 2033.

That will affect Florida communities along the Gulf of Mexico, including low-lying St. Petersburg neighborhoods like Shore Acres.

The study, published in the June 21 issue of the scientific journal Nature Climate Change, forecasts approximately seven days of high-tide flooding in St. Petersburg in 2023, but predicts almost 70 such days in 2033.

“It's going to get to the point where in some months, we’ll have a flood event almost every day,” said Gary Mitchum, associate dean of the University of South Florida College of Marine Science.

Mitchum worked with colleagues from the University of Hawaii to forecast how rising sea levels interact with tidal cycles.

Twice a month, the highest and lowest tides reach much more extreme levels than usual. These are referred to as spring and neap tides.

“Most people who live near the water would know that, but the thing that they might not recognize is that twice a year, the spring tides are higher than they are at other times of the year,” Mitchum said.

“And it also varies on times of about nine years and another for about 20 years. So the tides themselves change.”

The highest tides occur when the sun, Earth, and moon line up perfectly. That happens on that 20 year timescale.

“The better aligned they are, then the higher the tides due to the gravity pulling on each other,” Mitchum said.

At the moment, tides are on the decline. Between 2023 and 2033, the highest tides will get smaller as part of this natural cycle.

“The sea level rise is going up, but the highest tide we have is going down,” Mitchum said. “So it's kind of been flat in terms of the number of times you get a flood event.”

In 2033, however, the highest tides will start increasing again.

That shift will be compounded by sea level rise, which researchers say will result in a rapid increase in flood events.

“From 2033 to 2043, we expect to see 67 events per year, so an increase of almost a factor of 10. That's a pretty phenomenal change,” Mitchum said. “And it's due to this tide effect on top of the increase in sea level.”

Under this forecast, researchers warn that in some months, perpetual flooding could happen almost every day.

“To put that in perspective, I live in Shore Acres in St. Petersburg. We're subject to these high-tide flooding events. It's not a lot of water, but it's enough that I have to change the route that I drive to work on,” Mitchum said.

“I have to worry about that four or five times a year. We're now talking about having to find a new route to work every day.”

High-tide flooding causes public inconveniences such as frequent road closures, overwhelmed storm drains, and compromised infrastructure.

It can also disrupt local economic activity by reducing the number of visits to nearby businesses.

“If people aren't able to drive…maybe they'll decide to stay home, instead of going out to dinner,” Mitchum said.

He added that policy makers should be working with researchers on high-tide plans that maximize people’s safety while minimizing disruption.

“Sea level rise is just one part of climate change. It’s a much bigger problem,” Mitchum said. “So when we talk about these things, we need to think about adaptation and mitigation.”

“By reducing emissions, and pulling down the level of greenhouse gases, we can slow the rate of warming. Mitigation is a tough subject to talk about, because there are certainly costs associated. But by reducing the amount of damage that will be done, it will save us a lot of money.”

VIDEO: 27-year Sea Level Rise (Scientific Visualization Studio / NASA)

This visualization shows total sea level change between 1992 and 2019. Since 1992, seas around the world have risen an average of nearly 6 inches. Blue regions are where sea level has gone down, and orange/red regions are where sea level has gone up.

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Jacob Wentz
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