Flash floods hit New York City on Friday, putting 8.5 million people on warning and turning streets into rivers across Brooklyn and Queens. The scenes of inundated highways and subway platforms brought memories of Hurricane Ida, which just over two years ago, traveled up to New York from Louisiana, bringing some of the most intense rainfall the city has ever seen, and killing more than 40 people.
Friday’s storm had different origins, arising primarily from a weather pattern called an “inverted trough” that’s settled over the Northeast. But what’s similar is the volume of rain that poured from the skies in a brief amount of time, overwhelming the city’s sewer system, and the degree to which New Yorkers felt entirely unprepared or forewarned about what to expect.
New York’s vulnerability to flooding has been exposed again and again, beginning with Hurricane Sandy in 2012. To understand what the city has been doing about it, and why it’s been so hard to mitigate, I called up Daniel Zarrilli, the city’s chief climate policy advisor under former Mayor Bill De Blasio. Our conversation has been lightly edited for clarity.
How does what you’re seeing today compare with what happened the last time New York City saw serious flash flooding, two years ago, during Hurricane Ida?
I mean, this all feels fairly familiar. Ida was record-breaking, but it was what happened two weeks before that I think really stunned everybody. It was Hurricane Henri. That broke the record. I think the number was like 1.94 inches of rain per hour at Central Park. It was the most intense rainfall the city has ever seen. And then Hurricane Ida, two weeks, later broke that record again by about 50%. And you saw the devastation all over the city. Basement apartments flooded. People died. It was a terrible tragedy in the city.
This morning, what I saw at the Central Park reading was just a hair more than what Hurricane Henri had been. Today would have been record-breaking had it happened two years ago. But of course, we know what’s happening with our climate. And we know that the warmer atmosphere holds more water. And we’re seeing more and more of these devastating and high intensity rainfall events.
What are some of the things that the city has done to try to improve its resilience to flash flooding?
The city has been working on these questions for quite some time. Several billion dollars went into drainage infrastructure in southeast Queens. The city has built thousands of bioswales and rain gardens to capture water, to keep it out of the sewer system, and help reduce the combined sewer overflows. All that helps with flooding.
But I think what we’re seeing here is that it’s that high intensity that matters most. The drainage network is designed to manage about an inch and three quarters of rain in an hour, and we’re seeing numbers that are higher than that. The infrastructure just can't handle it. These high intensity rainfalls and climate change is just continuing to stress that aging infrastructure that we have all across the city.
And you know, these events are not always citywide events. You can have much more localized, high intensity rainfall and it makes it much harder to predict where those things are going to happen around the city. What might seem like a similar rainfall event, if it happens geographically in a different way, the impacts are wildly different as well.
Does that mean that the solutions that we have just don’t match the scale of the problem, or does it mean that we’re just not going fast enough or doing enough?
I think it’s a little bit of both. I think there’s clearly more infrastructure investment that’s needed to handle higher intensity rainfall events, but I think we have to recognize that there’s going to continue to be these events that are going to exceed the design capacity of the infrastructure. We need to get more creative about how we handle the overflow so that it channels itself down a differently designed street to get to the harbor, instead of into the subway or into someone’s basement. The ability for the system to, sort of, fail more gracefully, instead of more catastrophically, is I think a really important way to think about this.
And the other is, how we communicate this in advance. We can’t just tell people something bad’s going to happen. We have to be much more direct on what they can do about it. That might mean things like closing schools or asking businesses to declare work from home, or something that doesn’t put people out in the conditions while it’s happening.
What are the biggest challenges to improving the city’s preparedness for flooding?
We’re a very high density city. Building out new infrastructure in a dense urban environment, whether it’s along the coast or it’s within our streets and our drainage networks, you’re trying to do new things on top of layers of existing built environment and infrastructure. That’s really complicated. And that doesn’t lend itself to easy answers.
I live on Staten Island and one of the really successful measures that has been accomplished is the blue belt network. It’s a really great solution for handling intense rainfall and filtering water and water quality and biodiversity. But it’s not the kind of thing that works everywhere, because it needs a fair amount of space. We need to apply similar creativity to find solutions that can be more rapidly implemented.
But again, you run into this big, dense urban environment with layers of existing infrastructure, and there are not easy answers.
International Council on Clean Transportation