New York City floods because its aging sewer system was built to handle only 1.75 inches of rain per hour in most areas, and climate change is delivering storms that regularly exceed that threshold. But the problem goes deeper than old pipes. The city’s geography, its miles of concrete and asphalt, rising sea levels, and even the ground physically sinking beneath certain neighborhoods all combine to make flooding one of New York’s most persistent and growing dangers.
A Sewer System Built for a Different Climate
The single biggest reason streets flood in New York is that the drainage network underneath them simply cannot keep up. FEMA found that the drainage system across much of the city, including parts of Queens where flooding has been deadliest, is designed to handle just 1.5 inches of rain per hour. When storms dump more than that, the water has nowhere to go but up through storm drains and across streets, sidewalks, and into buildings.
Making matters worse, roughly 60% of New York City relies on a combined sewer system. That means stormwater and raw sewage travel through the same pipes. During heavy rain, those pipes fill beyond capacity, and a mix of rainwater and untreated sewage pours out of 398 overflow outfalls directly into surrounding waterways. The city’s combined sewer system is one of the largest in the country, discharging approximately 18 billion gallons of this combined sewage every year. The overflow doesn’t just pollute rivers and harbors. It also means the system is losing drainage capacity at exactly the moment neighborhoods need it most.
More Concrete, Faster Runoff
In a natural landscape, soil and vegetation absorb a significant share of rainfall. New York City is roughly 72% impervious surface: rooftops, roads, parking lots, and sidewalks that repel water instead of absorbing it. When rain hits concrete, it moves faster and concentrates in low-lying areas rather than slowly filtering into the ground. This dramatically increases both the speed and volume of stormwater that the sewer system has to manage all at once.
Extreme Rainfall Is Getting Worse
The storms hitting New York are not the same storms the sewer system was designed for. Multiple studies have documented significant increases in both the frequency and intensity of extreme precipitation across the northeastern United States since the mid-to-late 20th century. The IPCC projects that this trend will continue throughout the 21st century, meaning the gap between what the infrastructure can handle and what the sky delivers will only widen.
Hurricane Ida in September 2021 made this painfully clear. Record-breaking rainfall rates overwhelmed the city in a matter of hours, turning streets into rivers and filling basement apartments with water. Eleven people died in flooded basement apartments, 10 in Queens and one in Brooklyn. Many of those buildings sat in low-lying areas, and some were built on or near historical water bodies that had been filled in decades ago. The deaths were directly tied to the unprecedented amount of rain that fell within a single hour.
Parts of the City Are Physically Sinking
Some of New York’s most flood-prone areas face an additional problem: the ground beneath them is subsiding. A NASA-led study identified several hot spots where land built on artificial fill is slowly sinking. Two notable areas in Queens sit on old landfills. One runway at LaGuardia Airport is sinking at about 0.15 inches per year. Arthur Ashe Stadium, also in Queens, is subsiding at roughly 0.18 inches per year, a problem significant enough that engineers installed a lightweight roof during renovation to reduce the building’s weight.
Other sinking zones include the southern portion of Governors Island, built on 38 million square feet of rock and dirt from early subway excavations, and coastal neighborhoods like Coney Island in Brooklyn and Arverne by the Sea in Queens, both constructed on artificial fill. When land sinks even slightly, it puts infrastructure closer to water tables and tidal levels, compounding the effects of both rainfall and coastal flooding.
Rising Sea Levels Add Coastal Pressure
New York is a coastal city surrounded by water on nearly all sides, and those waters are rising. State projections estimate sea levels will increase between 0.5 and 2 feet by 2050. Under a median scenario, the region could see 18 inches of rise by the 2050s. Under a high-end scenario, 30 inches is possible by the same decade. Higher baseline water levels mean storm surges push further inland, tidal flooding reaches streets that used to stay dry, and the sewer system has less room to discharge during heavy rain because outfall pipes are already partially submerged.
For a city where critical infrastructure, housing, and transit lines sit at or near sea level, even modest increases translate into significantly more frequent and severe flooding events.
Basement Apartments Face the Greatest Risk
New York has hundreds of thousands of basement and below-grade apartments, many of them home to lower-income residents and immigrants. These units sit at the lowest point in any building, which means floodwater reaches them first and fills them fastest. During Hurricane Ida, the 11 people who drowned were all in basement apartments. Researchers found that these buildings were concentrated in low-lying areas, sometimes on land that was once a stream, pond, or wetland before being filled in and built over. The historical water still follows its old paths during extreme rain, pooling in exactly the places where those apartments sit.
What the City Is Doing About It
New York has been working on the problem from multiple angles, though progress is slow relative to the scale of the challenge. One approach is “cloudburst management,” a strategy that uses a combination of underground storage tanks, larger sewer pipes, rain gardens, and trees to absorb, store, and redirect stormwater before it overwhelms the system. The city announced four initial Cloudburst Hubs in January 2023, located in Corona and Kissena Park in Queens, Parkchester and Morris Park in the Bronx, and East New York in Brooklyn. The first completed pilot project wrapped up in 2025 at the South Jamaica Houses, a public housing complex in Queens. Additional pilots are underway in East Harlem, St. Albans, and Far Rockaway, with more designs in progress for Brownsville and Homecrest.
The city also runs the Bluebelt program, which preserves and enhances natural drainage corridors like streams, ponds, and wetlands instead of replacing them with underground pipes. These systems temporarily store stormwater, reducing flood damage to nearby properties while also filtering pollutants and creating green space. Urban wetlands are especially valuable in a city dominated by hard surfaces, because they counteract the rapid runoff that impervious streets and rooftops create.
These programs represent a shift in thinking, from trying to pipe all water underground to working with natural and engineered landscapes that can hold water in place. But retrofitting a city of 8.3 million people takes decades and billions of dollars, and the climate is changing faster than the infrastructure can adapt. For now, the combination of outdated sewers, intensifying storms, rising seas, sinking land, and vast expanses of concrete means flooding in New York is not an anomaly. It is a structural feature of how the city was built and where the climate is heading.