Miami-Dade County

Report: Tidal flooding to be more frequent in Miami, Key West as seas rise

A woman boards a Miami-Dade Transit bus on Alton Road at 10th Street in Miami Beach after the driver pulled up to a ramp, making it somewhat easier to avoid a huge puddle.
A woman boards a Miami-Dade Transit bus on Alton Road at 10th Street in Miami Beach after the driver pulled up to a ramp, making it somewhat easier to avoid a huge puddle. MIAMI HERALD STAFF

Tidal flooding in Miami and Key West will increase dramatically over the next 15 years as seas continue to rise, according to a study released Wednesday just as annual high tides begin creeping toward Miami Beach.

Using data collected earlier this year in the White House’s National Climate Assessment, the Union of Concerned Scientists looked at Miami and Key West, along with 50 other communities deemed vulnerable to rising seas driven by climate change. By 2030, researchers concluded, Miami could flood eight times more frequently. By 2045, the number could increase steeply to about 230 floods per year. Key West could fare far worse, with 45 floods a year, or more than three a month, by 2030.

“That level of inundation is going to be game changer for us in South Florida,” said Nicole Hammer, assistant director of climate change initiatives at Florida Atlantic University, who helped write the report’s section on Florida. “We won’t be able to function the way we do now unless we take pretty aggressive measures to begin to adapt.”

With some cities already experiencing flooding up to four times more frequently than in 1970, the authors decided to take a closer look at the forecast for communities from Freeport, Maine, to the Texas coast under scenarios mapped out in the National Climate Assessment. The assessment, released earlier this year, was the Obama administration’s attempt at compiling an authoritative report on climate change, the president’s science advisor, John Holdren, said last week.

Along with shorter winters and more severe droughts, the assessment found that a two-degree increase in temperature over the last century had helped drive rising sea levels and increased flooding along the East Coast. Many parts of the coast are expected to see a foot of sea rise by 2045.

While hurricanes and coastal storms are expected to cause the most severe flooding, the Union of Concerned Scientists focused on regular, and predictable, floods associated with high tides.

Every month, high tides occur when the earth, sun and moon align. Twice a year when the moon is closest to the earth, these tides, called spring or king tides, can be significantly higher. A king tide is expected to peak on Thursday, when Miami Beach will test its $15 million investment in stormwater pumps.

To reach their findings, the report’s authors relied on tidal gauges in communities along with coastal flood advisories issued by the National Weather Service. They also considered an intermediate amount of polar ice melt — a factor in rising seas that has vexed scientists.

“We can’t ignore the fact that we’re seeing ice melt,” said Erika Spanger-Siegfried, one of the study’s authors. “But... these are massive ice sheets with really complex dynamics that we’re just getting a handle on.”

By 2030, the report found, half of the 52 communities studied can expect to average more than two dozen tidal floods every year. Some regions, like the Mid-Atlantic, could see flooding triple in frequency. Flooding will also reach farther inland, the report said. When strong winds or heavy rains coincide with high tides, flooding could be far worse.

“Such floods take on a new level of gravity and significance when they become chronic,” the report warns.

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