Warming Planet May Double Odds of New York Flooding, Study Says

New York’s odds of being flooded by a one-two punch of extreme rain and surging seas have more than doubled in the past 80 years, a change scientists say may be linked to global warming.

The number of so-called compound flooding events -- combining heavy precipitation and a high storm surge -- have “increased significantly” for much of the coastal U.S., affecting cities from New York and San Francisco to Boston and Galveston, Texas, researchers said in a paper published Monday by the journal Nature Climate Change.

Researchers found an increased connection between storm surges and high precipitation, phenomena that forecasters and urban planners often treat as independent events when preparing for storms, said lead author Thomas Wahl. How much of the change is due to global warming or natural variation is unclear, but the data suggest policy makers should reconsider where they build infrastructure and how flood zones are drawn, Wahl said by telephone.

“Cities need to come up with revised methods” of planning for floods, said Wahl, a professor of civil and environmental engineering at the University of South Florida St. Petersburg. “The actual impact of these compound events depends very much on the local situation: what infrastructure is in place, how much drainage is available.”

One particular scenario the researchers studied for New York, an almost 4-foot storm surge (1.2 meters) combined with 5 inches of rain (12.7 centimeters), is now anticipated once every 42 years, compared with the once-in-a-century expectation in the 1940s. A similar storm, Tropical Storm Doria, caused an inflation-adjusted $868 million worth of damage when it barreled up the East Coast in 1971.

How much of the increased risk is due to human-caused changes in weather patterns is unclear and will require more study, Wahl said. Other factors may also play a role, including natural variations in the climate and sea levels, he said.

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