NYC's Subway Flooding Isn't A Fluke. It's The Reality For Cities In A Warming World

NYC's Subway Flooding is Not a Fluke. It's a reality for cities in a warming world
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Global warming is causing dangerous and disruptive flooding in underground railway systems all over the globe. In recent years, flooding at stations and tunnels has disrupted services and left passengers stranded in Boston, London and Washington, D.C.

The problem is now more urgent than ever thanks to multiple high-profile subway floodings caused by summer rainstorms.

The remnants of Hurricane Ida caused flooding in large parts of New York City's subway system overnight. Mayor Bill de Blasio issued an emergency travel ban and advised residents to "stay away from subways" as it was possible for up to 10 inches to fall in certain parts of the region within hours.

It is the third consecutive summer that New York's subways have been flooded. This is also the first time that the National Weather Service has issued a flash flood warning for the city. Boston's underground tracks have been repeatedly submerged by heavy rains.

Subway floods in other areas have proved deadly. After being trapped by flash floods, 13 people died in Zhengzhou (China) in July. The videos were so heartbreaking that they showed people trying to breathe in a shrinking air pocket as the water rose.

Slobodan Djordjevic is an engineer at University of Exeter who specializes on flooding underground train systems. Djordjevic spent a lot of his life studying flooding in subway tunnels. He says that he was shocked at what he saw in China. "I was actually pondering if this was real."

Climate-driven torrential rainfall is the cause of the flooding in China and elsewhere around the globe. Zhengzhou received almost a year's worth in precipitation in one day. In one afternoon, remnants of a tropical hurricane dumped more than a month's worth rain on New York City earlier this summer. Djordejevic says that flooding has affected dozens of subway systems worldwide, with the possibility of hundreds of thousands of people.

This has caused tension between the need for reliable and low-emissions mass transportation options and the rising cost of underground transit in a more humid world. It is costly to keep water out of stations and tunnels, particularly in areas with old, leaky subways built for the twenty-century climate.

The federal government could provide some assistance. Congress is currently working on an infrastructure bill that allocates $66 billion to rail. This huge cash infusion could be used to fund the retrofitting and construction of new lines for areas that rely on cars, as well as funding existing subway systems.

Djordjevic states that every city should conduct a thorough review of the flood risk to its underground system. Authorities need to be strategic about where they plan to build new lines, stations and tunnels in the future.

Many Asian cities are well ahead of the curve

Many American cities have spent a decade adapting their subway systems for a wetter climate. The Boston transit authority started waterproofing stations and protecting tracks vulnerable to sea-level rise. New York City spent millions to flood control the nation's most extensive underground railway system after Hurricane Sandy. The transit authority in Washington, D.C. has spent millions waterproofing leaky tunnels, and plans to spend more to keep water out from station entrances and vents.

Andy Off, Executive Vice President for Capital Delivery at the Washington Metropolitan Area Transit Authority, stated that "We are investing more today in water mitigation than ever before." There is also an emergency flood response. The unit monitors inclement weather and can alert workers to flooding hotspots. Workers can also check underground pump stations for water before they arrive.


However, keeping water out of your home is a constant struggle. Washington, D.C.'s metro system dates back nearly 50 years. New York City's subways and Boston's are older. The sidewalk or street is flush with the air vents, making it easier for water to flow in. Station entrances are often located in low-lying areas or constructed in ways that channel water down stairs or escalators.

Tina Hodges, an ex-analyst at the Federal Transit Administration, says that older systems were built for the climate of the future. She wrote a report in 2011 about climate risks to public transportation in the U.S. Northeastern United States. There has been a 67% rise in heavy precipitation in this region.

Similar results can be found in several European cities such as London and Berlin. Passengers have taken strikingly similar videos in recent years of water flowing into subway stations in cities thousands miles apart.

Perhaps newer subway systems in flood-prone areas of Asia could offer insight into how to adapt. As the Zhengzhou disaster this summer made clear, Asian cities are at the forefront of climate-driven subway flooding. The fact that these newer systems are often more protected against flooding and fatalities underlines the need for adaptation.

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He says, "There are many lessons to be learned from Asian cities and how to manage flooding of underground trains." In Taipei, for example, authorities raised the entrances of stations to prevent flooding due to cyclones. Researchers in Kyoto, Japan built a scale model of a subway station elevator and created a flash flood simulation to show how much water people can safely cross. This was done to test whether there were any emergency plans to close stations during storms. Although Bangkok, Thailand has had a flood warning system for years to protect passengers, underground train flooding has been a problem.

Djordjevic says that many subway systems in Asia were built earlier than those in Europe and the U.S., which makes them more suited for the current climate.

Hodges says that the U.S. has a higher percentage of larger cities adapting to and preparing themselves for flooding due to their greater resources. Large transit agencies have a growing number of resilience experts, who are available to collaborate with climate scientists and engineers in order to find solutions that protect passengers and trains from flooding. These resources are more rare in smaller cities.

Hodges states that there are certain barriers to adaptation to climate change. One of these is the difficulty in interpreting climate science into actionable information that engineers and planners can use.

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New train tunnels remain attractive despite flood risk

Underground trains are still a great option for many cities. New York City has continued to expand its subway lines since Hurricane Sandy. San Francisco is expanding its subway system, even though it faces flooding from rising sea levels.

Fort Lauderdale is one of the most vulnerable places to flooding in the country. A new underground train line would reduce traffic and allow residents to travel by train into downtown.

There have been some questions about the idea of investing in underground infrastructure in what is known as "Venice of America". The city's newspaper editorial board criticized the plan and suggested that the train cross a major river through a bridge rather than through a tunnel.

While Mayor Dean Trantalis recognizes that climate-driven flooding can be a problem in his city, he dismissed concerns about train tunnel flooding. He says, "If you have the right pump stations and the technology to predict heavy rains and other things like that, I've lived in Fort Lauderdale almost 40 years and my tunnel has never been flooded." The train will be kept underground to reduce congestion caused by railroad crossings.

Experts agree that it is important to consider the cost of future infrastructure and the climate. Many places are seeing sea level rise, including Florida. New train systems that are built to last for 30 years or longer will have to withstand significantly higher tides and more severe storms.

Djordjevic says that "when it comes to Florida's coastal areas, there will be some areas that will need to be abandoned, or protected at very, very high costs." These decisions should be carefully considered.