Commuters in The Bronx and Manhattan faced severe flash flooding at subway stations last Thursday as storms dumped more than four inches of rain on the city in less than 24 hours.
Viral videos captured commuters wading through waist-high water at 157th Street and water barreling down Dyckman Street - both in upper Manhattan. The Dyckman Street station alone took on 28,000 gallons of water. These videos are a reminder of more dramatic floods like Hurricane Sandy in 2012, and a preview of what to expect as rain-induced flooding becomes more common and climate change accelerates.
Up to 20 percent of all New York City subway station entrances - more than 400 in total - could be affected by an extreme rain scenario, also known as a “once-a-century” flood event, according to Regional Plan Association (RPA) analysis.
Wet subway woes are not new in New York. Even on a dry day, about 14 million gallons of water are pumped out of the subway system. Now, however, “once-a-century” flood events occur every couple years, regularly inundating stations despite earnest efforts from the Metropolitan Transportation Authority (MTA). The agency has invested $2.6 billion in resiliency projects since Hurricane Sandy, including fortifying 3,500 subway openings like vents, staircases, and elevator shafts against flooding.
Some causes of subway flooding are beyond the transit agency’s control. For example, at 157th Street and in other neighborhoods, runoff water flooded streets, sidewalks, and stations because nearby drains and catch basins were either clogged or not designed to handle the magnitude of these flood events.
While some observers have rightfully pointed out the subway system was not designed to account for climate change nearly one hundred years ago, the reality remains: our transit infrastructure is still unprepared for climate change, particularly rain-induced flash floods.
To demonstrate the magnitude of the New York City subway system’s adaptation needs, Regional Plan Association (RPA) staff mapped station entrances and compared this information with flood models recently published by the Mayor’s Office of Resilience. The Department of Environmental Protection, the agency in charge of our water supply and sewer systems, developed two rain-based flood models: a moderate scenario based on two inches of rain per hour, and an extreme one based on three and a half inches per hour.
These models show places of localized flooding and the impacts of potential blocked storm drains and outfalls from sea level rise. In both scenarios, the maps demonstrate that the city’s sewer infrastructure was not designed to handle rainstorms of such magnitude.
Under the moderate scenario, a dozen or so station entrances would be affected by deep and contiguous flooding - which is more or less what New York City experienced last week. This partially explains why the majority of the transit system was up-and-running, with major disruptions avoided.
Climate change will make those events more intense and frequent.
Under the extreme scenario, up to 20 percent of all station entrances - more than 400 in total - could be affected by some type of rain-induced flooding. 227 entrances would be affected by nuisance flooding, 156 entrances would be affected by deep and contiguous flooding, and 21 entrances would be affected by the predicted high tides in 2080.
New York City and the wider metro region should begin to address flood events in the subway system by tackling two big barriers to meaningful climate change adaptation: cost and coordination.
Proactive climate change adaptation projects will likely be some of the most expensive we undertake in the next generation. Yet today we mostly pay for them by retroactively relying on federal funds in the wake of natural disasters. The federal government should contribute funding toward New York’s climate change adaptation needs, but it should be proactive and not reactive. The negotiations happening at the federal level right now over an infrastructure bill, for example, ought to account for climate change adaptation on a very significant and ambitious scale.
RPA’s Fourth Regional Plan also outlines new and more effective ways to fund adaptation projects like instituting climate adaptation trust funds through an insurance surcharge, establishing a Regional Coastal Commission that would help prioritize funding for resilience projects, and implementing congestion pricing to help raise funds for transit improvements.
Future development can - and should - also contribute to the city’s climate adaptation efforts. The city should prioritize transit oriented development and land value capture mechanisms that aim to reduce or slow the release of stormwater into the right of way, sewer systems, and transit infrastructure. This includes private property incentives for green infrastructure including grant funding for green roofs and a large-scale retrofit program kicking off this year.
The MTA’s current five-year capital program includes about $140 million directly associated with future drainage projects. The Mayor’s stormwater resiliency plan indicates that the city’s 2021 10-year capital plan includes $4.6 billion for sewer improvements. The agency has committed $3.8 billion to sewer upgrades citywide in the past decade. While these investments are welcome, it is unclear the extent to which these commitments will improve the resilience of our transit system when it faces rain-induced flooding.
The relatively small amount of resiliency funding in the MTA’s capital plan (compared to investments made after Superstorm Sandy), coupled with the uncertainty around the city’s stormwater resiliency commitments to transit, raises important questions. The responsibility for mitigating the impact of rain-induced flooding on transit seems to be falling into a technocratic gap. Runoff water, however, does not care about political boundaries or agency jurisdictions.
Hurricane Sandy flooded the MTA South Ferry subway station in 2012.
New York City is still trying to spend federal disaster relief funds from Hurricane Sandy before they expire in September 2022. While the Mayor blames the slow pace of spending on federal bureaucracy, New York City’s own agencies ought to become more nimble, too.
To adapt the city’s transit infrastructure to climate change and rain-induced flooding, we need strategic operating and capital investments and nimble, coordinated agencies to implement them. More in depth analysis should help identify priority areas with greater precision and the instances where interagency coordination is most needed.
As the window of opportunity to adapt to climate change narrows, all city agencies, especially DOT and DEP, must immediately align with each other - and with the MTA -in order to complete projects more rapidly to mitigate the impacts of rain-induced flooding. New York City can achieve this in part by promoting greater inter-agency coordination and implementing a comprehensive planning framework, where budget and capital programs would be aligned with current and future needs.
While those recent subway station flooding videos are shocking to watch, we know these events may soon become commonplace unless we invest, coordinate, and act now.
