In Parts of New York City, a Vexing Mix of Stormwater and Sewage Have Made Flooding the ‘New Normal’ – Inside Climate News

As climate change intensifies, New York City is increasingly facing weather extremes. Currently, the city is on drought watch, and recently, wildfires have erupted in Brooklyn’s Prospect Park and neighboring New Jersey and Connecticut.

The city is forecast to have a dry winter, and the risk of the first drought emergency since 2002 mounts every week without rainfall. 

In recent years, the city has also often suffered from an over-abundance of water. Last September, the subway flooded, as did highways, when the remnants of tropical storm Ophelia blew through the city. 

Extreme rainfall events, which are likely to become more frequent as climate change intensifies, are threats not just to people and property, but also to the ecosystem of the Hudson River and its estuaries. 

This month, the New York-New Jersey Harbor Estuary Program hosted a conference where environmental activists, scientists, city employees and community organizers came together to discuss the health of these ecosystems, as well as that of the communities on its shoreline. 

The wellbeing of the two parties are inextricably linked.  

“The same thing that was plaguing the estuary was impacting my community,” said Pamela Pettyjohn, the president and founder of the Coney Island Beautification Project, a nonprofit organization focused on environmental awareness and community resilience.

The conference took on a somber tone in light of recent election results, with many city and state employees, as well as local environmental groups, anticipating a more complicated path to cleaning up the city’s waterways. Their chief obstacles are sewage outflows and stormwater.

New York City, like many dense urban areas, has a history of filling in surface stream channels, as well as inland marsh, which would have once absorbed and conveyed stormwater to larger bodies of water. Instead, the city is dependent on a nearly 200-year-old network of 7,500 miles of sewer pipes to collect and convey sewage and stormwater to 14 wastewater treatment plants.

Around 60 percent of the city’s sewers are part of a combined system, which means stormwater and sewage run through the same pipes to the wastewater treatment plants. When the sewer system is overwhelmed during extreme rainfall events, both sewage and stormwater are redirected out to the Hudson River and its estuaries in combined sewer overflows.

At the same time, since Local Law 172 passed in 2018, city agencies are required to develop maps to identify areas of the city that will be most exposed to flooding due to climate change. Coastal flooding has been at the forefront of resilience conversations in New York since Superstorm Sandy landed on these shores in 2012, killing 43 residents and flooding entire neighborhoods. 

But extreme rainfall events, and the flooding associated with them, are much harder to predict, and their impacts are difficult to model.

“One of the reasons that there’s such a challenge is because they can occur at such small spatial and temporal scales,” said Bernice Rosenzweig, a professor of environmental science at Sarah Lawrence College. “They’re not well represented in our conventional ways of making climate change projections.”

Rosenzweig also co-chairs the Flooding Workgroup of the New York City Panel on Climate Change. According to her group’s 2024 report, flooding in some inland areas of the city from short extreme rainfall events, which are often referred to as cloudbursts, are projected to become 19–24 percent more intense due to climate change. 

Another report, published in a 2024 Springer Nature journal, found that nearly a third of the city’s roads could potentially be flooded during these cloudbursts. It also discusses the potential for future storm surge, bolstered by sea level rise, to cause backflow into the sewer system, ultimately pushing the water through outfalls and back up through storm drains. 

The uncertainty surrounding the potential for extreme rainfall events can also be traced back to another important factor—humans.

“When doing projections for extreme rain, the biggest source of uncertainty is also what people will do in the next few decades, in terms of human greenhouse gas emissions,” said Rosenzweig. 

City Plans to Manage Sewage and Stormwater

The city’s Department of Environment Protection has developed 11 Long-Term Control Plans to reduce combined sewer overflows in water bodies. These often make use of both engineered solutions, like retention tanks for stormwater or sewer improvements, and green solutions, like restoring marshes and establishing green roofs or rain gardens—gray and green infrastructure. 

The Financial District and Seaport Climate Resilience Plan is a part of the Lower Manhattan Coastal Resilience Project, which will protect a part of the city hit hard during Superstorm Sandy. The plan includes a proposal to extend the Manhattan shoreline into the East River by a city block, creating an elevated flood zone that would also serve as a redesigned waterfront for the community. 

Arcadis, a sustainable design company, has partnered with the city to deliver the plan. Joel Kaatz, national technical expert and co-lead of the global flood risk and stormwater management practice with the company, extolled the importance of addressing the issue of stormwater accumulation behind the proposed raised waterfront. 

“The plan also proposes a large pump station for rainfall that falls behind that coastal protection system, and that can provide a lot of benefit for the sewer system in the upstream and surrounding area,” said Kaatz, and new sewer lines that connect to the pump station. 

The Department of Environmental Protection has also begun more ambitious efforts to alleviate pressure on the sewer system, including unearthing parts of a Bronx waterway—Tibbetts Brook—so that the clean water from the stream no longer enters the city’s sewers. The process is called “daylighting.”

“We have to think about the processes, the strategies, that we can use that will allow us to store water, and safely convey water,” said Rosenzweig. “You really have to think of what magnitude of storm that any type of infrastructure is designed for, and also how it functions within the landscape of the city.”

Cloudburst hubs—structures like sunken basketball courts which retain stormwater during heavy rainfall—and the Adams administration’s general plans for increasing green infrastructure in the city, also contribute greatly to efforts to alleviate the pressure on the sewer system.  

But despite the Department of Environmental Protection’s efforts to manage stormwater, many of the city’s plans are delayed, while others don’t meaningfully reduce combined sewer overflow. And, according to some scientists, some of the obstacles the city faces could simply be insurmountable. 

Not Completely Smooth-Sailing

In April, New York City Comptroller Brad Lander released a report on the city’s preparations for a flash flood event. It found that, when Storm Ophelia hit last September, 63 per cent of the Department of Environmental Protection’s 51 catch basin cleaning trucks were out of service. Cleaning catch basins helps prevent the streets from flooding, as plastic and other garbage can stop drainage into the sewer system. 

The city’s sewer system was not designed for the amount of water that now falls on the city during intense storms, which has led the city to its current two-pronged green and gray infrastructure plans to combat flooding from heavy rainfall. 

The sewers also regularly need fixing, with emergency repairs making up at least 8 percent of the Department of Environmental Protection’s annual budget. 

Though the department has added sewers in some areas over the course of the past two decades, a larger overhaul of the system would be near-impossible due to the cost and the disruption to city residents. There is also very limited subterranean space left in the city, particularly because the water table is quite high in some areas. 

Even if a wide-ranging effort was made to reform parts of the sewer system, experts like Rosenzweig insist that the city would not know what amount of rainfall to plan for due to the uncertainty surrounding cloudbursts, and more generally, climate change.

“How do you do a cost-benefit assessment when you don’t know what the weather is going to be like in the future?” said Rosenzweig. “You don’t know what the probability of various types of storms is going to be.”

The comptroller’s report also revealed that a majority of the department’s stormwater infrastructure are delayed or over budget. Timelines for projects often stretch into the next two decades, ultimately letting millions of gallons of sewage and dirty stormwater enter the city’s waterways in the meantime. 

Recently, the city announced the redesign of the long-term control plan at Newtown Creek—a small waterway that separates Brooklyn and Queens and connects to the East River—causing delays in the reduction of combined sewer overflow into the creek. 

Though the redesign would lead to a 67 percent reduction in overflow into the creek, rather than 62 percent, community leaders want to see further reductions if the project is to be delayed to 2040. 

“If we’re going to get a 10-year delay, we want to make sure that there’s substantial benefits being done in the meantime,” said Willis Elkins, executive director of Newtown Creek Alliance. The alliance is a local organization that works to improve the environment around the creek.

Elkins and his team have advocated for further planned reductions of combined sewer overflow into the creek, particularly as New York City leaders have committed to eradicating nearly all overflow into the waterways by 2060.

“If you’re re-examining the system in general, you should try to make it as substantial as possible so we can get closer to something like a 90 percent reduction,” said Elkins. “It seems like it would be more cost effective if their goal is to actually get to zero” 20 years after the project is finished.

The Department of Environmental Protection, asked for comment, responded by providing the city’s most recent stormwater management update.  

Despite the city’s best efforts, there are some instances where flooding is unavoidable, particularly due to the amount of impervious surfaces in the city. The city lacks space to store water during large storms—a problem that has no easy solution. 

“If you have water running in your sink, and you put it on a trickle, it’s going to go down the drain, but if you put five gallons of water into your sink, it’s going to overflow,” said Dr. Jennifer Cherrier, a professor of Earth and Environmental Sciences at CUNY, and the founder of Waterway Ecologics, a company that designs nature-based solutions to drainage issues. “People need to understand that we’ve paved everything, so where’s the water going to go?”

Kaatz, the stormwater management expert at Arcadis who has extensive experience partnering with the city for stormwater and storm surge resilience plans, sees a future where the city works to ensure that assets like hospitals, transit infrastructure and major highways remain operational during a flood. This type of well-developed flood warning system, he said, prevents loss of life and helps maintain access to critical services. 

“It’s about redefining what we mean when we say ‘manage’ or ‘be resilient,’” said Kaatz. “You have to acknowledge that there’s going to be events that exceed the capacity of your infrastructure.”

Clean Water—a Unifying Issue

Though progress is slow in New York, the desire for healthy ecosystems in the state’s waterways seems to be a unifying issue, even across partisan lines. 

For Suffolk County, Long Island, just a two-hour drive from the city, improving sewage infrastructure has been one of the few things local officials and residents can agree on. 

Proposition 2, which was voted in during this last election cycle in a landslide, would create a small increase in county sales tax to fund the expansion of the region’s sewer system in certain areas, and the update of most residents’ septic tanks. 

Around 74 percent of homes in this region are not connected to a sewer system, and instead make use of often old-fashioned personal septic tanks and cesspools to dispose of sewage. 

Currently, most of these tanks do not adequately remove nitrogen from sewage, and are leaking into the groundwater underneath residents’ homes, ultimately polluting the Long Island Sound and surrounding water bodies. 

“There’s no other place that has a population of 1.5 million people that doesn’t have sewers—that’s absurd,” said Adrian Esposito, the vice president of Citizens Campaign for the Environment, a local nonprofit that has been pushing for the passage of Proposition 2 for years. “In New York, we’re supposed to be treating our sewage, not drinking it and swimming it.”

“Rather than think about flooding when we’re in the middle of an Ophelia or Ida or a Superstorm Sandy, we just need to understand that it’s something we’re going to be living with. It’s the new normal.”

— Jennifer Cherrier, CUNY professor of Earth and Environmental Sciences

Higher nitrogen levels can lead to lower dissolved oxygen in the water, which can choke out marine organisms. Advocates for the bill expect a slow improvement in water quality, with the most marked changes only being observed around a decade in the future. 

Despite the bill’s gradual effects, residents and environmental advocates are excited about the future.

“In light of climate change, we are worried that the storms and the warming water are going to slow our progress,” said David Ansel, vice president of water protection at Save the Sound, an environmental organization that helps steward the Long Island Sound. “So it’s even more important than ever that we do what we can control, which is to improve our infrastructure.”

Back in New York City, local officials are increasingly taking a holistic approach to sewage and stormwater infrastructure. They are working to understand where water flows and accumulates, from upper elevation, through the city’s streets and sewers, and out into the river and sea. 

“It’s about focusing on areas that you know may have the most flooding problems, but also from a social vulnerability and equity standpoint, and recognizing that water doesn’t see the boundaries of a project,” said Kaatz. This is called a watershed-scale approach.

New rainfall models help show the city where flooding is likely to happen, ensuring that green and gray infrastructure can be placed in strategic locations. They also help inform residents whether their homes are likely to flood in the event of extreme rainfall. 

Cherrier hopes that these models help further encourage the city’s governing bodies to be more proactive when it comes to stormwater and coastal resilience—rather than reactive. 

“Rather than think about flooding when we’re in the middle of an Ophelia or Ida or a Superstorm Sandy, we just need to understand that it’s something we’re going to be living with,” said Cherrier. “It’s the new normal.”

Resilient Communities

Every year, the Brooklyn waterfront neighborhood of Red Hook hosts the Barnacle Parade, a celebration of their resilience in the face of Superstorm Sandy, which hit the area hard 12 years ago. 

In late October, residents dressed up in water-themed costumes and jubilantly marched through the neighborhood. A marching band slowly moved through the streets, as well as a litany of boatlike structures and laughing children.

The parade ended at Van Brunt and Pioneer Streets, where local vendors sold food and custom T-shirts, and local bands played for the many families gathered. A man atop a large rectangular float dubbed the “Wind-A-Bago” maneuvered a bubble machine, to the delight of the many children in attendance. 

Families played under a large blue tarp behind it, a representation of the water that devastated this community. 

Despite the enduring memory of flooding during Sandy, there is a palpable sense of excitement among residents. They are still here, and that is cause for celebration.