Coastal development, sea rise sent Hurricane Irma storm surge to more homes, study shows

Alex Harris, Miami Herald on

Published in Weather News

MIAMI -- Sea rise and development have put more Florida property at risk to hurricane storm surge flooding -- about 43 percent more -- according to a recent study that looked at Hurricane Irma's effect with different sea levels.

NOAA Tidal gauges in Key West show that South Florida has seen about seven inches of sea level rise since the 1970s, which is part of the reason sunny day flooding has worsened in recent decades.

But when a hurricane blows through, that extra water becomes an even greater liability. Storm winds whip the water into buildings, busting through doors and swirling the contents of homes (or washing them away altogether.) Storm surge from Hurricane Irma alone affected 133,000 homes across Florida (45,000 alone in Miami-Dade) as the storm crawled up the spine of the state.

According to an analysis by First Street Foundation, that seven inches of sea rise, plus an explosion of coastal development over the last decades, led Irma to swamp 57,000 extra homes.

If development along the Florida coast had been frozen in 1970s, the seven inches of additional sea rise pushing farther inland would have affected 35,000 more homes.

That pace of development doesn't appear to be slowing anytime soon, nor does the rate of sea rise. Projections by the Southeast Florida Climate Compact, on which four South Florida counties base some of their decision making, predict 11 to 20 inches of sea rise from 1992 levels by 2050.

First Street chose the higher end of the curve, which is about 15 inches higher than today's sea levels. With that much sea rise, another 200,000 Florida homes would have been swamped by Hurricane Irma, and that doesn't account for increased development.

Last year, scientists measured around 3.9 feet of storm surge from Hurricane Irma. With 15 inches of sea level rise, Miami could see 5.4 feet of storm surge from the exact same storm.

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Scientists are "very confident" that climate change will make storm surge and rainfall worse, said Brian Soden, a professor of atmospheric sciences at the University of Miami's Rosenstiel School of Marine and Atmospheric Science.

"When you increase sea level the storm surge increases. That's one of the inevitable consequences of dealing with tropical cyclones in the future," he said.

Research used in the analysis shows that for every foot of sea level rise, scientists can predict an increase in about 15 inches of storm surge, about a 23 percent percent increase.

This is the sea rise advocacy organization's second such analysis of the impact of sea rise on hurricane storm surge. Researchers found that sea level rise was responsible for 20 percent of homes affected by storm surge in Hurricane Florence.

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