The climate crisis turns the world’s subways into flood zones

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Terrified passengers trapped in flooded subway cars in Zhengzhou, China. Water cascade down the stairs in the London Underground. A woman wading through murky water up to her waist to reach the New York subway platform.

Metro networks around the world are struggling to adapt to an era of extreme weather conditions brought on by climate change. Their designs, many of which are based on the expectations of another era, are outdated and investments in upgrades could be curtailed by a drop in ridership brought on by the pandemic.

“It’s scary,” said Sarah Kaufman, associate director of the Rudin Center for Transportation at New York University. “The challenge is how do we prepare for the next storm, which was supposed to be 100 years from now,” she said, “but could it happen tomorrow?”

Public transport plays a key role in reducing car trips in large cities, thereby limiting automobile emissions that contribute to global warming. If commuters are frightened by images of flooded train stations and start avoiding subways for private cars, transport experts say this could have major implications for urban air pollution and greenhouse gas emissions. tight.

Some networks, like those in London or New York, were designed and built over a century ago. While a few, like the one in Tokyo, have been successful in strengthening their flood defenses, the crisis in China this week shows that even some of the most recent systems in the world (Zhengzhou’s system is not even ten years old). ) can also be overwhelmed.

Modernizing flood metros is “a huge undertaking,” said Robert Puentes, managing director of the Eno Center for Transportation, a nonprofit think tank focused on improving transportation policy. “But when you compare that to the cost of doing nothing, it starts to make a lot more sense,” he said. “The cost of doing nothing is much more expensive.”

Adie Tomer, senior researcher at the Metropolitan Policy Program at the Brookings Institution, said subways and rail systems help combat urban sprawl and reduce the amount of energy people use. “Subways and fixed rails are part of our climate solution,” he said.

The recent floods are another example of the type of extreme weather conditions that are compatible with climate change around the world.

Just days before the Chinese metro nightmare, flooding in Germany left 160 people dead. The great heat waves have wreaked havoc in Scandinavia, Siberia and the Pacific Northwest in the United States. Wildfires in the Western United States and Canada sent smoke across the continent last week and triggered health alerts in cities like Toronto, Philadelphia and New York, giving the sun an eerie reddish tint.

Flash floods have also inundated roads and highways in recent weeks. The collapse of part of California’s Highway 1 in the Pacific Ocean after heavy rains this year has served as a reminder of the country’s fragile roads.

But more intense flooding poses a particular challenge to aging metro systems in some of the world’s largest cities.

In New York City, the Metropolitan Transportation Authority has invested $ 2.6 billion in resilience projects since Hurricane Sandy flooded the city’s subway system in 2012, including fortifying 3,500 subway vents, stairways and elevator shafts against flooding. Even in dry weather, a network of pumps discharges approximately 14 million gallons, mostly groundwater, from the system. Yet this month’s flash floods showed the system remains vulnerable.

“It’s a challenge trying to work within the constraints of a city with aging infrastructure, as well as an economy recovering from a pandemic,” said Vincent Lee, associate director and technical director of the water for Arup, an engineering company that helped modernize eight metro stations. and other facilities in New York after the 2012 storm.

London’s sprawling underground faces similar challenges.

“Much of London’s drainage system dates back to the Victorian era,” said Bob Ward, policy director at the Grantham Institute for Climate Change and the Environment in London. And this has a direct impact on the city’s metro system. “It is just not able to cope at this time with the increase in heavy rainfall that we are experiencing due to climate change.”

Meanwhile, the crisis in China this week shows that even some of the world’s newest systems can also be overwhelmed. As Robert E. Paaswell, professor of civil engineering at New York City College, said: “Subways are going to flood. They are going to flood because they are underground.

To help understand how underground flooding works, Taisuke Ishigaki, a researcher in the Department of Civil Engineering at Kansai University in Osaka, Japan, built a diorama of a city with a bustling metro system, then set off a downpour equivalent to about 11 inches of rain. in one day.

Within minutes, floodwaters pierced several subway entrances and began to hurtle down the stairs. Just 15 minutes later, the diorama platform was under 8 feet of water – a sequence of events Dr. Ishigaki was horrified to see unfold in real life in Zhengzhou this week. There, floodwaters quickly overwhelmed the passengers still standing in the metro cars. At least 25 people have died in and around the city, including 12 in the metro.

Dr Ishigaki’s research now informs a flood monitoring system used by Osaka’s vast underground network, where special cameras monitor surface flooding during heavy rains. Water above a certain level of danger activates emergency protocols, where the most vulnerable entrances are closed (some can be closed in less than a minute) while passengers are quickly evacuated from the metro via other outings.

Japan has made other investments in its flood infrastructure, such as cavernous underground cisterns and flood valves at metro entrances. Last year, private rail operator Tokyu, with support from the Japanese government, completed a massive cistern to capture and divert up to 4,000 tonnes of stormwater runoff at Shibuya Station in Tokyo, a hub major.

Yet if there is a major breach in the many rivers that flow through Japanese cities, “even these defenses will not be enough,” said Dr Ishigaki.

Public transport advocates in the United States are calling for pandemic relief funds to be allocated to public transport. “The scale of the problems has grown greater than what our cities and states can solve,” said Betsy Plum, executive director of the Riders Alliance, an advocacy group for subway and bus users.

Some experts suggest another approach. With more extreme flooding down the line, protecting subways at all times will be impossible, they say.

Instead, investments are needed in buses and cycle paths that can serve as alternative modes of public transport when subways are flooded. The natural defenses could also provide relief. Rotterdam in the Netherlands grew plants along its trams, absorbing rainwater through the ground and reducing heat.

“During the pandemic, you saw the way people got around by bicycle, the most resilient, least disruptive, cheapest, and low-carbon mode of transportation,” said Anjali Mahendra, research director at Ross Center for Sustainable Cities of the World Resources Institute, a Washington-based think tank. “We really need to do a lot more to connect parts of cities and neighborhoods with these cycle lanes that can be used to get around. “

Some experts question why public transport has to be underground in the first place and say public transport should take the street back. The street-level tram, bus systems and bicycle lanes are not only less prone to flooding, they are also cheaper to build and easier to access, said Bernardo Baranda Sepúlveda, Mexico City-based researcher at the Institute for Transportation and Development Policy. , a non-profit organization.

“We have this inertia of the last century to give cars so much available above ground space,” he said. “But one bus lane carries more people than three car lanes.”

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