New York City has thousands of underground apartments, and many residents are understandably worried about what the future holds for them as severe storms become more common in the Northeast. When the remnants of Hurricane Ida struck the tri-state area in early September, its torrential downpour killed 29 people in New Jersey, 16 in New York and one person in Connecticut. In New York City, 11 of the 13 victims died in flooded basements.
Investigators and researchers are unraveling the mixture of calamities that contributed to people perishing in these underground dwellings. Early signs point to an overwhelmed sewer system, legal basement apartments being built in low-lying areas and building code violations.
“Apartments in cellars and basements can be death traps,” said Reza Khanbilvardi, a professor of civil engineering and hydrology at City College of New York. When the soil is saturated during storms, the flow can be substantial, said Khanbilvardi.
Storms can threaten some basement renters if their dwelling doesn’t have enough exits or its windows are too small to fit through. This danger often occurs in cellar apartments (defined as being less than 50 percent above curb level as opposed to basement apartments, which have more than 50 percent of their walls above curb level).
According to the New York City building code, cellar apartments in one- and two-family homes are forbidden as a living space, and basement apartments must have one window in each room and a ceiling height of at least 7 feet. A spokesperson for the city’s Department of Buildings said five of the six properties where people died during Hurricane Ida were illegally converted cellar and basement apartments.
Along with structural issues, tenants in illegal apartments are often afraid to call for help because they risk getting kicked out of their residence, said Khanbilvardi.
Another culprit behind deadly flash flooding is New York City’s sewer system. It isn’t built to deal with storms like Hurricane Ida. New York is one of 772 U.S. cities with a combined sewer system—meaning stormwater on streets, sewage from homes and industrial waste share the same pipes. When heavy rain or repeat rainfalls overwhelm the system, runoff doesn’t happen as quickly as it needs to and can result in flooding. “We don’t have an empty sewer system waiting,” said Khanbilvardi.
The combined system can also result in raw sewage seeping into local rivers, which happened after Hurricane Ida and sickened Queens residents. Neighborhoods with high rise buildings and larger populations have bigger sewer systems—built with more capacity to handle high volumes of stormwater, said Khanbilvardi. But many residential enclaves in Queens and Brooklyn—those filled with one and two family units—just aren’t equipped to handle flash floods.
The New York City Department of Environmental Protection said it is working to separate previously combined sewers and create dedicated stormwater lines where possible. Gowanus, College Point and Canarsie are a few of the areas currently under construction.
Parts of Queens were built on marshy land, and some neighborhoods in the borough are in low-lying areas that are more vulnerable to flooding from storms and nearby creeks, streams and rivers.
“People who try to have inhabitable basements in those areas are gambling because there is often flooding,” said Clint Andrews, a professor of urban planning at Rutgers University. The Department of Buildings said they have received more than 3,000 self-reported notifications of storm-damaged properties across the five boroughs and will be conducting safety inspections. NYPD is investigating the illegal basement units where the fatalities occurred.
Despite the geographic pitfalls and structural violations, these apartments are an important source of affordable housing in New York City, said Rebekah Morris, a senior program manager at the Pratt Center for Community Development, which is part of NYC Base Campaign, a coalition created to make basement apartments safer. They also provide revenue for low-income homeowners, Morris said.
Morris thinks the city needs to focus on making these units habitable. “People are going to live in basements whether or not they’re legal. People need housing,” Morris added.
Brooklyn has similar landscape characteristics as Queens, but the former might have experienced less flooding and fewer deaths due to other factors such as stricter enforcement of building codes or better maintenance of sewers.
“When a storm like this one comes in, if you look at the street, you see many things, diapers, plastic bags, cans of coke,” said Khanbilvardi. Those items can cause clogging in sewers which decreases their capacity.
Urban flash floods also used to be less frequent partially because there weren’t as many paved areas, said Andrews. Now, New York City is heavily paved, which means much of the stormwater isn’t absorbed into the ground.
The structural and topographic issues in the city were exacerbated by Ida’s rainfall, which greatly exceeded some predictions. Khanbilvardi added that’s why there wasn’t an adequate warning in neighborhoods that faced severe flooding.
After the storm, New York City Mayor Bill de Blasio unveiled his Climate-Driven Rain Response Plan. He said the plan includes more aggressive pre-storm evacuations of streets and subway systems and a focus on a warning system, particularly for those living in basement apartments.
“It’s not like the rain we used to know. It’s just not. It’s a different reality of speed and intensity that we now have to understand will be normal,” the mayor said. The city’s Emergency Management agency has the ability to convert schools and other public buildings into shelters, but the city did not respond to questions about whether it is currently providing these shelters for people displaced by the storm. A representative for City Councilman Brad Lander said they are referring residents to the Red Cross, which is providing shelter in hotels throughout the city.
Stormwater flooding could be partially remedied by covering roofs with plants and vegetation, also known as green roofs.
“It’s like a sponge. It soaks up the water as it falls, and then it slowly releases it so that you don’t have that peak moment of rushing water that takes lives,” said Andrews. Creating permeable or absorptive surfaces can also help lessen the impact of flooding. The city’s Department of Environmental Protection said it had built in recent years more than 11,000 curbside rain gardens, infiltration basins and other green infrastructure practices to intercept stormwater.
As climate change intensifies storms in the New York City area, Andrews recommends tenants in basement apartments check that they have a second exit and can fit through it. This rule is especially valuable for tenants living at the bottom of hills.
“If you’re in a basin, you really do need to worry about inundation because you’re gathering water from all around,” said Andrews. Tenants and landlords should also check if water often pools inside the unit or outside during regular rainfall. That may be an indicator the drainage system isn’t optimal.
Sump pumps, a basin with a pump that senses water and automatically removes it, can help thwart flooding. But during extreme rainfall, pumps will get overwhelmed, and it’s crucial to have a plan for getting out.