Published on Sustainable Cities

Preparing Cities for Climate Change – Initial Lessons from Sandy

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NYC subway station damaged by seawater flooding during Hurricane SandyNew York City has been a global leader in proactively planning and preparing for climate change under Mayor Bloomberg and the city’s civic leaders. PlanNYC sets out clear goals and plans to reduce greenhouse gas emissions by more than 30% and to increase the resilience of our communities, natural systems, and infrastructure to climate risks. It already started the process of adapting to climate change, including elevating infrastructure such as wastewater treatment plant, and expanding “green infrastructure” like marshes along the coast to buffer and limit flooding impacts.

But the events triggered by the unprecedented hurricane Sandy haven shown that what has been done is still not sufficient. What can we learn from the disaster? There will be a lot of valuable lessons coming out in the months ahead, as emergency responses are still ongoing and reconstruction are yet to start. Here are three early lessons:

The chance of catastrophic events is likely under-estimated. Governor Andrew Cuomo, only half-jokingly, stated that “every two years we have a one-hundred-year storm”. Even with careful identification and study of the city’s vulnerabilities led by scientists and experts, the scale of the storm still surprised everyone. The flood level is two feet higher than the past floods. What is particularly tricky is the double whamming of the storm: timing of the storm surge coincided almost exactly with the time of the normal high tide, resulting in much higher level of flood. There are debates as to how much role climate change played in Sandy, but the fact that sea level in the city has already risen by up to one foot over the last century means that a storm would lead to much bigger flood. Also, Sandy moved over very warm waters in North Atlantic, certainly giving it more energy. No matter how important was climate change to Sandy, extreme events are likely to happen more often. The fact that events which were considered once in a hundred years now tend to happen every ten years or even more frequently means that there needs to be “a fundamental rethinking about our built environment”, as stated by Cuomo, including infrastructure and buildings.

Need for flood-proofing the subway system. One major surprise is the flooding of the subway system. Even though the transit agency has taken many preventive measures, such as covering entrances and vents, erecting flood walls, and readying pumps, each of the seven subway tunnels in lower Manhattan was flooded. Large amount of water in the tunnels and stations will take a lot of time to be pumped out. Even after the water is out, the salt water is likely to have damaged quite a lot of the electric equipment. Options to improve the resilience of the subway system, as laid out by a Daily Beast article, include higher entrances and ventilation grates, built in flood gates (such as Bangkok metro which withstood the large 2011 flood), more pumps with back-up powers, or even a “huge balloon” to plug tunnels.

Power back-up and fire hazard. The power grid has a lot of vulnerabilities, especially in densely populated city like New York. It is not surprising that multiple types of breakages occurred all over the city, from downed power lines in the outer boroughs to exploded transformers in downtown Manhattan. How to better prepare for power outage in face of its inevitability? It is critical to carefully plan for the back-up system for essential functions, such as pumps, as a power outage would prevent them from working when they are most needed during flooding. Many buildings have their own power backup system, but often they are installed in the basements that are subject to flooding, again preventing them from functioning when flooding and outage occur at the same time. Finally Sandy shows the need to prepare and prevent fire hazard from explosions caused by flooding.

As the recovery of New York City and the northeast US proceed, New Yorkers will learn and reflect more, and these lessons will be valuable for other cities. “The fundamental rethinking” would call for higher-level efforts, such as “ringing Lower Manhattan with a grassy network of land-based parks accompanied by watery patches of wetlands and tidal salt marshes”, a feat that was planned and implemented in Brazil’s Curitiba. There is also need to reevaluate past efforts to develop low lying waterfront areas.

What is clear is that cities, especially coastal ones, need to seriously raise their game on preparing themselves for increasing disaster risks in face of climate change. Many of the cities that the World Bank is supporting, such as Kolkata, Mumbai, Dhaka, Guangzhou, Ho Chi Minh City, Shanghai, Bangkok and Yangon, are even more vulnerable to coastal flooding than New York. There is even more work to be done there.

Photo: NYC subway station damaged by seawater flooding during Hurricane Sandy. Credit:
MTA Photos, Flickr



Ming Zhang

Practice Manager for Urban Development and Disaster Risk Management

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