Andrew Kelly / Reuters

Hurricane Sandy is the wake-up call.

Millions upon millions of people live in coastal cities — not just New York and the Boston-Washington corridor, Los Angeles, San Francisco, Miami, and New Orleans, but also many of the great cities in the emerging economies of Asia, India, and around the world. Their coastal locations are what fueled their growth in the first place, as a recent study titled "The United States as a Coastal Nation" [PDF] shows.

Cities, especially coastal ones, are critical components of the global economy. Just the world's 40 largest mega-regions — many of them located along coastline — account for roughly two-thirds of global economic output and nine in 10 of the world's innovations. The next several decades are primed to witness the greatest surge in urbanization in world history, and much of it will occur in coastal cities.

But coastal mega-cities are also susceptible to natural disasters, like Hurricanes Sandy and Katrina or the tsunami that led to the nuclear power plant meltdown in Japan. These great disasters appear to be occurring with increasing frequency, and prompt debates about their relation to global warming and climate change, as well as our cities' preparation for both storms and rising sea levels.

A 2007 Organisation for Economic Co-operation and Development (OECD) study [PDF] examined the world's cities that are most at risk for coastal flooding, looking at the levels of population and economic activity currently at risk as well as projecting out to 2070. The report notes that about 40 million people were "exposed to a 1 in 100 year coastal flood event" as of 2005. But by 2070, this risk increases to some 150 million people "due to the combined effects of climate change (sea-level rise and increased storminess), subsidence, population growth and urbanisation."

The maps below (from the report) chart the population and economic assets at risk currently and out to the year 2070, as population grows and the current pace of climate change continues. The exposure from coastal flooding is a feature of our spiky economic world, being highly concentrated in a small number of large global cities. When it comes to risk to population, the top 30 cities represent 80 percent of global exposure and just the top 10 represent roughly half of it. New York is among the major population centers exposed to coastal flooding, alongside Miami and New Orleans as well as Shanghai and Guangzhou, China; Mumbai and Kolkata, India; Ho Chi Minh City, Vietnam; Osaka-Kobe, Japan; and Alexandria, Egypt. The risk to population centers is roughly split between cities in the advanced and emerging economies. 

Map courtesy of the OECD study, "Ranking of the World's Cities Most Exposed to Coastal Flooding Today and in the Future" [PDF]
Map courtesy of the OECD study, "Ranking of the World's Cities Most Exposed to Coastal Flooding Today and in the Future" [PDF]

When it comes to economic assets, the risk shifts to wealthier cities in the advanced world, and becomes even spikier and more concentrated (see the table below also from the OECD report). As of 2005, the report estimated the economic exposure to coastal flooding to be roughly $3 trillion, or about 5 percent of global economic output. By 2070, the total asset exposure could rise more than tenfold reaching $35 trillion, more than 9 percent of projected annual global economic output. New York ranks third in terms of economic assets at risk to coastal flooding in 2070. Miami is first, Guangzhou is second, Kolkata fourth, Shanghai fifth, and Mumbai sixth. New Orleans and Virginia Beach also rank among the top 20.

Table courtesy of the OECD study, "Ranking of the World's Cities Most Exposed to Coastal Flooding Today and in the Future" [PDF]

Long Island, New York, on Oct. 30. (U.S. Coast Guard/
Petty Officer 2nd Class Rob Simpson/Handout/Reuters)

What can be done to mitigate this risk? 

Writing over at The Nation earlier this week, Mike Tidwell suggests that there appear to be three basic solutions: "(1) abandon our coastal cities and retreat inland, (2) stay put and try to adapt to the menacing new conditions or (3) stop burning planet-warming fossil fuels as fast as possible." Given that the first one is more or less impossible, he concludes, like most of us probably would, that coastal mega-cities need to do a combination of two and three.

That means we have to begin to make our cities, especially our global cities, more resilient. There is indeed a growing research literature on resilience.

2010 essay in Seed magazine explained the growing field of urban resilience, drawing upon two main premises:

The first is that humans and nature are strongly coupled and co-evolving, and should therefore be conceived of as one “social-ecological” system. The second is that the long-held assumption that systems respond to change in a linear, predictable fashion is simply wrong. According to resilience thinking, systems are in constant flux; they are highly unpredictable and self-organizing, with feedbacks across time and space.

The article goes on to note that the field emphasizes "tipping points," such as gradual climate change and crises like storms or market crashes. It states: "How much shock can a system absorb before it transforms into something fundamentally different? That, in a nutshell, is the essence of resilience." The article focuses attention on the issue of urban resilience in particular, and the inner-workings of "the medley of blue and green spaces, both natural and man-made, that can buffer a city against change." The article also poses some important questions for global cities and those who lead them:

Can the world’s mega-cities keep growing? Are other patterns of urban growth preferable? Urbanization is inevitable, but can it be directed so that cities can be harnessed as generators of innovation, and core contributors to future sustainability? As scientists make headway on these macro-issues, can they develop tools to help decision-makers build for social, economic, and ecological resilience?

Scientists have long warned of the vulnerably of coastal mega cities. Writing in Foreign Policy, John Seo noted last year that increasing globalization only heightens the impact of natural disasters and technology failures on the world, equating the potential future economic damage of a hurricane or earthquake to the destruction of a major war or nuclear weapon. In regard to information technology, he poses, "Are we putting the global economy's trillions of eggs in the largest electronic basket ever constructed?"

A sheen caused by spilled fuel shines on water left in a street by the storm surge of Hurricane Sandy in Lindenhurst, New York on Oct. 31. (Lucas Jackson/Reuters)

An article from The New York Times this past September explored New York City's vulnerability from flooding, casting an eerie hindsight over this week's storm. Dr. Klaus H. Jacob, a research scientist at Columbia University’s Earth Institute and an adviser to the city on climate change (also author of this predictive study), told the Times that subway tunnels would have flooded during Hurricane Irene had the storm surge been one foot higher. "We’ve been extremely lucky," he told the paper. "I’m disappointed that the political process hasn’t recognized that we’re playing Russian roulette." Today, repairs and service restoration are only just beginning in New York's flooded subway system.

The opportunity is to rethink infrastructure in terms of resilience, and not just rebuild it as it was (as this post in Scientific American points out). As University of Toronto professor Christopher Kennedy points out in his important book on The Evolution of Great World Cities, the definition of infrastructure goes far beyond roads, airports, tunnels, rail systems, subways and bridges and includes the rules, code and norms which govern how cities are built. His research points out that London's rise to global commercial dominance in the 17th century was fueled by its response to the catastrophic fires of 1666. These led to sweeping changes in the city's building codes and widening of its streets, which in turn led to increased densities, the adoption of new building technologies, and ultimately remade the city in ways that put it on a new growth trajectory.
The roadblock to building resilient cities, quite simply, has less to do with science and more to do with institutions and politics, as Steve Nash pointed out a couple of years ago in The New Republic.

For one thing, the politics of sea-level rise are still hazy—no one seems to agree on whether it’s a local, state, or federal responsibility. And Congress is not doing much to resolve these issues. The climate bill that passed the House last year merely calls for more research, even though more blue-ribbon panels seem superfluous at this point. “Do you need cost-benefit analysis to know that you’re going to protect Manhattan?” asks [Jim Titus of the U.S. Environmental Protection Agency]. “That you’re not going to allow the Jefferson Memorial to go underwater? That Miami is going to continue to exist?” Those aren’t trick questions. But, for now, they’re going unanswered. 

We'll be covering the issue of urban resilience on Atlantic Cities in coming weeks, starting with a conversation with Andrew Zolli, author (with Ann Marie Healy), of the important new book, Resilience: Why Things Bounce Back.

Top image: A largely unlit downtown Manhattan due to a power blackout caused by Hurricane Sandy on Oct. 30. (Andrew Kelly/Reuters)

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