Rooftop gardens in Brooklyn Heights, New York City.

Rooftop gardens in Brooklyn Heights, New York City. Alex Potemkin via iStock

The Living City: Weaving Nature Back Into the Urban Fabric

Urban ecologist Eric Sanderson focuses on the natural history of cities. In an interview with Yale Environment 360, he explains why recovering and restoring streams, salt marshes, and woodlands should be a vital part of how cities adapt to climate change in the 21st century.

As climate change intensifies, cities will be on the front line, suffering from increased flooding and life-threatening heat waves. City planners are searching for ways to make urban areas more resilient to these looming challenges, and chief among them is weaving nature back into the fabric of our cities.

Eric W. Sanderson, an ecologist and historian at the New York City-based Wildlife Conservation Society, says we need to bring back some of the features — like salt marshes, streams, and woodlands — that helped nature protect the landscape in the past. The author of the 2009 book Mannahatta: A Natural History of New York City, Sanderson is now working on an ecological history of New York’s outer boroughs, where disastrous floods have taken lives and destroyed homes in low-lying neighborhoods during recent storms.

In an interview with Yale Environment 360, Sanderson discusses the many ways that urban areas can adapt to sea level rise, worsening storms, and higher temperatures. Among his proposals are redesigning streets, restricting cars, planting trees and gardens on roofs, opening up long-developed ponds and streams, and devising new tax policies that encourage preserving critical ecological areas.

“We need to remember that a city wouldn’t exist except for the ecological fundamentals of the landscape,” Sanderson says. “Every problem that the city has ever faced, the landscape has already solved in some way, shape, or form.”

Eric Sanderson

Eric Sanderson Everett Sanderson

Yale Environment 360: Sea level rise poses a threat to cities around the world. In New York, places in Queens and Staten Island saw a lot of destruction in coastal areas during Hurricane Sandy and serious flooding later during big rain episodes. What do you expect in the years ahead with urban flooding?

Eric Sanderson: With climate change in New York City, the expectation is we’re going to have more precipitation and larger, more intense storms. For example, Hurricane Ida [in September 2021] was a wakeup call for lots of people. Where I live, we got 6 inches of rain in just a few hours. New York City gets on average 4 inches of rain per month. So, 6 inches is a month-and-half of rain in a couple hours. And it creates floods because the water doesn’t care about where you are. It just wants to go downhill as fast as possible and get to the ocean.

e360: You mentioned Hurricane Ida. Could you talk about Rock Hollow Pond in Queens, where a number of people drowned in their homes?

Sanderson: That’s a classic example. There was a pond at the base of the terminal moraine, the hills that go across Brooklyn and Queens. It’s on all the old maps up until about 1906, and then it got filled in and developed for housing. When we pave the streets or build buildings, we’re adding this impervious surface where the water can’t go through. That means the water’s going to run down that much faster into the low spots. That place has flooded for a long time. Ida wasn’t the only time. Several people got trapped in their basements and died. If we had understood the history and the ecology of the place, we never would have built there in the first place.

“Those ecosystems are going to restore themselves, whether we like it or not.”

e360: There’s a move in the Bronx to expose, or daylight, a former stream called Tibbetts Brook. What does it mean to daylight a stream?

Sanderson: It means taking it out of the sewer pipe and letting water run in the stream bed on the surface again. Streams not only convey water from one place to another, they also let water soak into the ground. You’re creating more space for the floodwaters to go. You’re also creating a place for vegetation to grow. So you’re doing lots of things simultaneously which have benefits for flood protection. But they also have benefits for the wildlife and for your experience of that place. It’s so much more pleasant to hear a stream bubbling in your neighborhood than it is to hear a highway.

e360: Cities are already built. There’s not a lot of scope for returning features like streams and ponds to the landscape is there?

Sanderson: Something is going to have to give up space. We are going to have to make some tradeoffs about where we live and where we park our cars and where we drive our cars. How many miles of street are there in New York City? Could we give up a few streets in order to have a few more streams?

e360: You and I recently visited Jamaica Bay, a tidal estuary that straddles the boroughs of Brooklyn and Queens. You talked about restoring salt marshes, sand dunes, and other natural features like coastal forest. Why is that a good idea?

Sanderson: In the past, we filled a lot of the salt marshes. That’s what happened to the wetlands in lower Manhattan. It’s why some neighborhoods are vulnerable to flooding today. And I feel bad about it. People bought houses or set up their businesses, not knowing any of this. And now with sea level rise, the water’s going to come up. The question is, what do we do about it?

Flooded train tracks in the Bronx in the aftermath of Hurricane Ida, September 2, 2021.

Flooded train tracks in the Bronx in the aftermath of Hurricane Ida, September 2, 2021. Spencer Platt / Getty Images

e360: You propose bringing back the ecosystems that used to exist there.

Sanderson: That’s right. Those ecosystems are going to restore themselves, whether we like it or not. Once your house starts to flood on every high tide, it is a salt marsh again. You can’t live there anymore. And we can accelerate that process by choosing to take care of the people who live there, finding a better place for them to live, and then taking out the infrastructure.

It seems to me the only way forward. It’s just very difficult because it’s not really compatible with our sense of property, which is we draw these lines on the map, and we think that those legal lines in your property deed are more real than the land and the nature itself of that spot. Somehow, we need to get our legal and social and economic system to understand that the land changes over time, that it’s not a constant. It’s actually a dynamic living entity.

e360: What do you think of proposals to build mechanical barriers like sea walls in coastal areas?

Sanderson: When you harden the shore by putting a cement barrier, you actually increase the high tides elsewhere. There have been some nice studies on this. When you bulkhead, you get more high tides. You’re actually increasing the magnitude of the tides, so you’re making it worse for somebody else that’s in the same area. Nature likes soft edges that absorb the energy of the waves and help keep the tidal range within limits.

“We have all these incentives to pour pavement onto the landscape, but too few incentives to restore it.”

e360: Many American airports, including JFK in New York, are built on former salt marshes. You suggest that we tax people who use JFK, maybe a dollar per passenger, and use that money to help restore Jamaica Bay.

Sanderson: All of our airports are on old marshes, not just JFK, but LaGuardia as well. Newark Airport is built on salt marshes. Reagan National in Washington, same thing. Billions of dollars of goods move in and out of JFK airport every year, and millions of people. We have this global good. Can’t there be some very small amount of money from this massive river of economic value that’s created by the airport that goes back to help address the pain and the suffering that the airport caused to local nature?

e360: And tied into that, you have also said that real estate taxes in urban areas should be based on the ecological value of the place. How would that work?

Sanderson: That’s right. Property taxes don’t have to be just assessed on the market rates of our housing. You could build an ecological assessment in it. The value that you’ve taken from nature by having your house there could be part of the assessment of the property taxes you pay.

My home on City Island [in the Bronx] means that a forest can’t be there anymore. I’ve basically taken all the benefits that forest gave to the public and displaced that public good for my own. That should be part of my property taxes, my payback to the community.

Wetlands, for example, are more valuable in general than forests because of all the flood protection services and all the biodiversity benefits that they provide. Building on them should be taxed at a higher rate. You would get to a point where it wouldn’t make any sense to develop that next wetland, because it would increase the taxes so much on everybody. It could actually lead to a joint effort to try and protect the most important ecological areas.

A rendering of Manhattan before Europeans arrived.

A rendering of Manhattan before Europeans arrived. Markley Boyer / The Mannahatta Project

e360: Is this sort of thing happening now anywhere in the U.S.?

Sanderson: In some cities your sewage bill accords with how much land your house covers, or if you tear up your driveway and turn it into a garden your storm water fees go down. But for the most part, we have all these incentives to pour pavement onto the landscape, but too few incentives to restore it.

e360: Climate change, and even now the ongoing pandemic, underline the fact that cities are inevitably a part of the natural world. Do you see urban planners becoming more sensitive to incorporating nature into their designs in the future?

Sanderson: Yes, I think urban planners, architects, landscape architects, are all thinking about the environment in a much more serious way than they did even a decade or two ago. The problem is that there tends to be no economic benefit associated with these things. Because we don’t actually evaluate the value of nature in our economic system, there’s no way for them to put it on the balance sheet. Our land planning processes, our legal process, our political processes don’t even admit this kind of information, so they just can’t respond to it — that’s the challenge.

e360: From my 31-story apartment building in Manhattan, I look out over a sea of roofs that are covered in asphalt. There’s nothing growing on most of them. This is a huge expanse of real estate that could potentially be covered in vegetation.

Sanderson: That’s right. Imagine you planted green roofs on all of those buildings. And for the ones that are strong enough, especially some of the older buildings that could hold more soil weight, you could have shrubs and even trees on them. You could rebuild a forest at the top of the building level. It would cool the city considerably during heat waves.

“Every problem that the city has ever faced, the landscape has already solved in some way, shape, or form.”

There’s also a benefit in just seeing green. There have been some really interesting studies that people who are in hospitals and have a window looking out on a green space, they heal faster. And workers are more productive when they have windows and look out on green space.

e360: Futuristic portrayals of cities often show them as being even more highly built, with huge, interconnected buildings and lots of vehicles buzzing around both on the ground and in the air. I take it your vision of the future city is different from that.

Sanderson: We need to remember that a city wouldn’t exist except for the ecological fundamentals of the landscape. Every problem that the city has ever faced, the landscape has already solved in some way, shape, or form, whether that’s flooding from coastal storms or long-term droughts or how to process carbon out of the atmosphere. All these problems have been solved by nature.

We need to take ecology in urban areas seriously, but also take seriously what’s great about the city, its people, its creativity, the innovation that flows from it, and then try to imagine a form of the landscape that can work for both — that can allow the tremendous variety and productivity of nature to shine through and also be a great place for people to live and to work.