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Subway Flooding: Expect More

Commuters on the Upper West Side of Manhattan wait in a stalled subway during the morning rush hour Wednesday, Aug. 8, 2007. Most subway lines in the city were experiencing delays or diversions after torrential rain caused flooding.
(Image: © AP Photo/Richard Drew)

The likely intensification of extreme weather events from global warming could mean that urbanites have more events like last week’s subway flooding in New York City to look forward to in the future.

The flooding and subsequent paralysis of New York's subway system—from nearly 1.5 inches of rain falling in just an hour—raised concerns about the subway system's infrastructure and the fate of the infrastructures of coastal cities worldwide in the face of extreme events that could become more frequent in our warming world.

"This is the kind of thing that we probably will see more of," said Kathleen Miller, an economist at the National Center for Atmospheric Research who studies the effects of climate change on society.

Stronger storms, higher seas

When an intense thunderstorm dumps a considerable amount of rain in a very short time, the ground cannot absorb the water quickly enough, so flooding occurs.

While the frequency of thunderstorms might not change, they are more likely to be intense in a warming world, climatologists say, because warmer air holds more moisture. This means that rain is more likely to come in short, intense bursts than in longer, gentler rainfall events.

"You've got more atmospheric moisture for a storm to draw on," Miller explained.

"All storms reach out and grab the available water vapor and concentrate it, and so it rains harder when it does rain," agreed climatologist Kevin Trenberth, also of NCAR, in an email interview.

Gradually rising sea levels are also a problem for dealing with subway flooding, as higher sea levels make it harder to pump out the water from the tunnels and could make the storm surge from nor'easters and hurricanes reach farther ashore.

City sewer systems, wastewater treatment plants, and water supply plants could all also be affected by intense rains and sea level rise.

"The current setup isn’t going to drain as well with higher sea levels," Miller told LiveScience.

Aging infrastructure

NCAR postdoctoral fellow Ilan Kelman says that much of the current infrastructure in the United States, not just in New York, is nearing the end of its life and isn't equipped to cope with these types of events and so requires investment to improve it.

Asked about what kinds of improvements the MTA plans to make in the wake of last week's flooding, MTA spokesman Mike Charles said that such a discussion was premature until the review report requested by New York governor Eliot Spitzer comes out sometime next month.

But flooding concerns are always on the MTA's agenda, he noted—even on dry days, pumps pull out about 13 million gallons of water a day from the subway tunnels.

As to whether climate change is being factored into the MTA's considerations for infrastructure upgrades, Charles said that "it's too early to say on that… they're not ignorant of it, but it's so speculative at this point."

But those who study the effects of climate change say that the time to start adapting infrastructure to those possible impacts is now.

"If we move quickly now, we could avoid the most serious consequences," said climatologist Radley Horton of Columbia University.