How Ida dodged New York’s flood defenses

“The problem is, we’re seeing these impacts and these changing storms faster, and the adaptations just aren’t keeping pace,” says Lauren McPhillips, a hydrologist at Penn State University who studies urban flooding.

New York City has been relatively forward thinking when it comes to flood preparedness, says McPhillips. For years, the city has implemented more permeable architecture, like green roofs and rain gardens, and improved pumps and drainage pipes. These improvements intensified after Sandy.

“We have learned a lot of lessons from Sandy,” said New York Governor Kathy Hochul in an press conference the day after the thunderstorms. “We have restored resilience; our coastal shores are in much better shape than they were before. But where we have a vulnerability is in our streets.

Sandy is a big part of any discussion about flooding in New York City. But the difference between the 2012 hurricane and Ida illustrates the complex flood threat the city faces due to climate change. Sandy caused an intense storm surge, where the ocean rushed into the city. Ida poured inches of water all over town in a short period of time, a problem sea barriers and other coastal protection cannot solve.

While New York City and other coastal areas are more vulnerable to sea level rise, any urban area can experience something called storm flooding, the kind caused by precipitation. “The way we developed New York City caused the flooding problem,” says Timon McPhearson, researcher in urban climate resilience at the New School and member of the New York City Panel on Climate Change.

Impervious surfaces like concrete cause water to flow downwards rather than sinking into the ground as might be the case in meadows or forests. And if enough water flows together, the consequences can be fatal.

“We literally have to rethink the city to solve the problem.”

Timon McPhearson

With contributions from researchers like McPhearson, New York City drew up plans to improve its defenses against flooding caused by storms. A prospective storm water resilience plan published in May 2021 included a flood risk assessment in the city and proposed solutions ranging from social strategies, such as educating local city councils about flood risks, to engineering techniques such as more green roofs and rain gardens.

And the city’s environmental protection department is considering plans for areas that are particularly affected during the most intense storms. The Cloudburst Resilience Study, completed in 2018, reviewed strategies for dealing with extreme rainfall events. Pilot plans in a frequently flooded area of ​​Queens included green infrastructure such as flooded walkways in a park, as well as a basketball court designed to hold water during major flooding.

But implementing these or any other stormwater management solution would require significant funding, and some would take a decade to design. “We literally have to rethink the city to solve the problem,” says McPhearson. And he expects the price to be high, possibly hundreds of billions of dollars. In some cases, he says, research is already suggesting how to protect the city from flooding, but raising the money and the political will to act remains a barrier.

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