The risk of flooding in New York City is 20 times more common than they were in the late 1800s, according to a new study. 

Sea levels around Metropolis have risen by a foot-and-a-half since measurements taken in the 1850s. This is similar to readings taken in other coastal cities around the world. However, the storm tide in the city has risen by around one foot. This is the highest seawater level during storms, including both the surge from the disturbance, plus any astronomical tide. 

Due to this increase in the storm tide, researchers concluded the nation's largest city is now 20 times more likely to flood than it was at the time of the American Civil War. Stefan Talke of Portland State University led the study, examining the effects of major storms on the Big Apple. 

His team found that "10-year storms," can cause sea levels to rise around New York City by 78 inches. Back in 1844, that depth was just 67 inches. The Manhattan Sea Wall is just 69 inches tall, and will likely be breached once every four or five years, according to the new study.  

"What we are finding is that the 10-year storm tide of your great-great-grandparents is not the same as the 10-year storm tide of today," Talke said

Hurricane Sandy delivered high winds and rain to the Atlantic seaboard in 2012, and formed a storm surge of 14 feet, the highest recorded in New York City since 1821. The subway system in the city begins to flood when sea levels rise by 10.5 feet. 

Sea Level information was recorded from data collected by the U.S. National Archives. Where data was missing, Talke and his team used contemporary news reports to determine the height of the ocean. That information was then compared to climatic data for the same period. 

Wetlands around the giant city have disappeared, holding rainwater that would have gone into the aquatic systems. The Lower New York Bay shipping channel has been further excavated, doubling its depth to accommodate cruise ships, adding to difficulties. 

The study found three of the nine highest sea levels ever recorded in the city have taken place since 2010. The years since 1990 have witnessed eight of the 20 highest levels ever recorded. 

Michael Bloomberg proposed a $20 billion program aimed at protecting the metropolis from floods, when he was mayor in 2012. This plan would have included construction of "Seaport City," a collection of homes and businesses near the water. 

Investigation of flood risk in New York City has been accepted for publication in the journal Geophysical Research Letters.

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