Infrastructure protectionA Subway Flood Expert Explains What Needs to Be Done to Stop Underground Station Deluges

By Klaus Hans Jacob

Published 3 September 2021

Subway stations in New York were inundated with water following heavy rain on 1 September 2021, and other cities around the world have also experienced similar inundations. “Climate change isn’t a matter of the future; its effects are happening right now,” says one expert.

Subway stations in New York were inundated with water following heavy rain on 1 September 2021. But the Big Apple isn’t alone – over the last year we have seen similar images in other major cities, including London and Zhengzhou in China.

The Conversationspoke with Klaus Hans Jacob, a geophysicist and flood expert who analyzed New York’s subway system before and after 2012’s Hurricane Sandy, about the ongoing – and increasing – flood risk to coastal underground transportation systems and what city planners can do to prepare and protect.

Are instances of major subway floods increasing? And if so, why?
In New York over the last month or so we have had three subway floods – first due to a heavy downpour, then from Tropical Storm Henri and now Hurricane Ida. Meanwhile, we have seen similar floods in cities across America and the world.

I think the message should be pretty clear by now: Climate change isn’t a matter of the future; its effects are happening right now. Warmer oceans means more moisture in the atmosphere, and as that moisture encounters cold air, it all comes down on the cities like the proverbial cats and dogs.

It is not necessarily a problem just for coastal cities. Ida, for example, left havoc across the entire interior of the eastern United States. But, of course, many major metros – from London to Amsterdam to Marseilles to New York – have been built next to major rivers or on the coast. This makes them vulnerable to excess water through rising tides or heavy rain. In the latest case in New York, it was from above, but the flooding from Sandy came from coastal surge.

How does the age of some of these subway systems affect flood risk?
When the subway was initially built in New York starting in 1904, no one was thinking of sea level rise or torrential rains. And so the fundamental design of the underground system did not take those phenomena into account.

We know better now. For the past 20 years, it has been clear that more severe storms are an inevitable outcome of human-made climate change.

But despite having a couple of decades to do something about it, we are still in a reactive mode rather than being proactive. Essentially city officials are cleaning up the mess after the storm, rather than taking measures like relocating infrastructure or protecting it.