Most of New York City — more than 70% — can’t absorb rain due to all its concrete and pavement. This often leaves water falling from the sky with no place to go, leading to catastrophic and deadly flash floods.
These calamities are especially common during cloudbursts, defined as a sudden but brief concentrations of heavy precipitation that typically accompany unusually hot weather, such as summer thunderstorms.
Scientists expect the problem to worsen with climate change.
To combat this, the New York City Department of Environmental Protection proposed last month to create a series of infrastructure installations that would transform portions of the five boroughs into super sponges.
The Cloudburst Management plan will turn available outdoor public surfaces and subsurfaces into layers that can absorb, capture, or divert precipitation. Using technologies such as porous pavement and collection basins installed below recreational facilities such as playgrounds, it can handle up to 2.3 inches of hourly rainfall, or an extreme storm one might expect to occur once every 10 years.
The project’s final coverage area is undetermined at the moment, as well as its price tag.
Ultimately, the program is designed to reduce property damage by alleviating the burden on the city’s 150-year-old sewer system. Most precipitation flows through these sewers and is diverted directly into one of the municipal waterways or wastewater treatment plants. Currently, the system can only handle 1.75 inches of rain per hour. When that is exceeded, flooding can happen.
“We are not really putting all of our eggs in one basket, just relying on the sewers,” Dr. Pinar Balci, assistant commissioner at the DEP, told Gothamist. Instead, the DEP is using a variety of solutions working cohesively together in areas where they are tailored to be most effective.
The DEP has been planning Cloudburst since 2017, piloting and testing various options to keep water from pooling in hazardous places. Its long-term vision is to expand the program by building “hubs,” a cluster of various stormwater resiliency projects concentrated around major flooding hotspots. At the end of the year, the agency will announce its first four sites.
A likely location for a Cloudburst hub is the New York Hall of Science in Queens. During Hurricane Ida, about half its exhibits were destroyed. The facility sits at a low point, and is vulnerable to flooding. Using a combination of porous bike and parking lanes along with surface and subsurface rainwater collectors, the DEP plans to reduce flooding not only at the museum but in the surrounding neighborhoods, too.
The city is funding Cloudburst with municipal and federal monies such as FEMA’s Building Resilient Infrastructure and Communities grant. President Joe Biden's administration recently doubled this resiliency program’s funding to nearly $2.3 billion following a $200 million boost via the Bipartisan Infrastructure Law.
Cloudburst would not have been able to prevent flooding from last year’s remnants of Hurricane Ida — record-breaking rainfall of more than 3 inches in a single hour. But it's designed to be an immediate and effective helping hand during a downpour, including lesser storms that still cause flooding, property damage, and fatalities citywide.
New York City is very wet – it’s going to get wetter
The average yearly precipitation in the metropolitan area is increasing at nearly an inch per decade. That’s projected to escalate further — by up to 11% – in less than 30 years alongside a rise of more frequent severe storms.
These weather events can have devastating effects. The remnants of Hurricane Ida killed more than a dozen people in New York City, most of whom were inside flooded basement apartments.
In the aftermath, the city released a report titled “The New Normal,” which cited stormwater management as a priority in combating future flooding.
Catastrophic costs come with being unprepared for rain. As a result of Hurricane Sandy, New York City incurred $19 billion worth of damage. The storm recorded more than 40 fatalities and crippled transportation systems including the flooding of all train tunnels into Manhattan. Basic services were temporarily unavailable leaving 2 million people without power and phone service for nearly two weeks.
This flooding is further exacerbated by sea level rise, which has risen twice as fast in New York City relative to the global average, according to the DEP. This increase in ocean levels also raises the water table, which means the soil cannot absorb as much water. When soil is easily saturated, more storm water will run off into streets and homes, increasing the chance of floods.
Flooding isn’t just caused by rainfall from above, according to Dr. Klaus Jacob, a geophysicist and climate expert at Columbia University's Climate School. He said in the past, many neighborhoods depended on wells for their water supply. Now that people no longer pump water from the Earth, the groundwater levels are higher.
“Rising groundwater levels mean that if it rains a little bit, that's enough to cause some flooding because the water can't infiltrate into the ground. So, it finds its way out to the street and the sewer system,” Jacob said. “Of course, under heavy rains, it gets worse. There are things coming from above when there are things coming from below.”
Absorb. Capture. Divert.
The sewer is the key component to the city’s routine stormwater management and the Cloudburst plan.
Upgrades are already in progress in southeast Queens, a flooding hotspot. The de Blasio administration invested about $2.5 billion for this segment of the system alone, according to the DEP, which said it improves about 70 miles of sewers annually. That’s about 1% of existing sewers.
But at that rate, it will take more than a century to completely overhaul the system. Projected sea level rise and precipitation levels are design factors for the new enhancements.
“The stormwater resilience vision for New York does have sewers as its kind of baseline – a first level of defense,” said Erika Jozwiak, a program manager for infrastructure at the Mayor's Office of Resiliency.
Some components of Cloudburst allow city surfaces to absorb more water. Green infrastructure such as rain gardens can fit into road and sidewalk medians with native plants. By using grading and openings gaps in the curb, rainwater is diverted into a sunken area where it can be absorbed through the soil. When the ground becomes saturated, the excess water is diverted further or stored in tanks. Beach 67 in Rockaway has rain gardens in its medians that include underground water tanks.
While natural storm protection is the DEP’s favored resiliency tool, Balci said it has limitations. Streets, sidewalks, and parking lots cannot be easily transformed into greenspace, but they can still be improved to absorb and divert runoff.
Porous pavement is an alternative to the traditional asphalt road, bike lane, sidewalk or even a recreational surface such as a playground. When it rains, this permeable material can absorb rainwater for storage or diversion below ground.
These penetrable surfaces are already piloting in residential parts of Queens and the Bronx, where there are 17,000 linear feet of porous pavement. City officials are currently designing another 300,000 linear feet in Brooklyn and the Bronx.
Often used in conjunction with porous pavement are methods for storing water captured during a downpour. Dry ponds and underground tanks are examples of rainwater collection, which can be integrated into recreational centers such as a schoolyard or a basketball court.
A pilot project for the South Jamaica Houses, an eight-block Queens NYCHA complex home to about 2,600 residents, is entering the construction phase. The project will consist of basketball courts made from porous blacktop. Below the courts, large underground storage collects water. And because it’s sunken into the ground and enveloped by a wall of concrete bleachers, the court itself will also become a pool during storms that can hold additional rain.
The DEP estimates the new courts will cost $4 million-$5 million, which also includes the excavation of two grass lots for underground water storage.
Jacob, from Columbia, contends that these engineering solutions are expensive — and temporary. Eventually, these projects will have to be replaced, upgraded or maintained, he said.
“We need a long-term vision,” Jacob said. “I'm not sure whether that's the case for this particular project.”