(Bloomberg) -- New York’s odds of being flooded by a one-twopunch of extreme rain and surging seas have more than doubled inthe past 80 years, a change scientists say may be linked to globalwarming.

The number of so-called compound flooding events -- combiningheavy precipitation and a high storm surge -- have “increasedsignificantly” for much of the coastal U.S., affecting cities fromNew York and San Francisco to Boston and Galveston, Texas,researchers said in a paper published Monday by the journal NatureClimate Change.

Researchers found an increased connection between storm surgesand high precipitation, phenomena that forecasters and urbanplanners often treat as independent events when preparing forstorms, said lead author Thomas Wahl. How much of the change is dueto global warming or natural variation is unclear, but the datasuggest policy makers should reconsider where they buildinfrastructure and how flood zones are drawn, Wahl said bytelephone.

“Cities need to come up with revised methods” of planning forfloods, said Wahl, a professor of civil and environmentalengineering at the University of South Florida St. Petersburg. “Theactual impact of these compound events depends very much on thelocal situation: what infrastructure is in place, how much drainageis available.”

One particular scenario the researchers studied for New York, analmost 4-foot storm surge (1.2 meters) combined with 5 inches ofrain (12.7 centimeters), is now anticipated once every 42 years,compared with the once-in-a-century expectation in the 1940s. Asimilar storm, Tropical Storm Doria, caused an inflation-adjusted$868 million worth of damage when it barreled up the East Coast in1971.

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

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