Wednesday, Nov. 28, 2012

How to Save the City

It was called the Watersnoodramp, which in Dutch means "flood disaster" — and it was nothing less. The North Sea flood of 1953 was the result of a high tide meeting an unusually strong storm — the same combination that made Superstorm Sandy so destructive — resulting in a coastal surge that inundated the countries around the North Sea. Lives were lost in England, Scotland and Belgium, but the most severe impact was felt in the Netherlands. The old dikes and other sea defenses built around the Dutch coast proved powerless to stop the surge. Radio stations at the time didn't broadcast at night, when the flood was at its worst, so few Dutch residents living in harm's way received the warning to evacuate, and nearly 2,000 people died after the sea swallowed the coastline. With much of their country positioned below sea level, the Dutch were no strangers to the threat of a coastal storm, but the 1953 flood would prove one of the worst in the nation's history.

It was also a turning point for the country. Soon after the floodwaters receded, the Dutch launched an ambitious program to strengthen and extend the seawalls and other defenses that had failed to protect them. That eventually led to the creation of the Delta Works — a $13 billion, 640-km-long system of levees, seawalls, dikes, locks and dams designed to ensure that something as catastrophic as the 1953 flood never hits the Netherlands again. The Delta Works — which features movable parts that allow Dutch planners to keep waterways largely unblocked except in the event of a major storm — is designed to protect the Netherlands from 1-in-10,000-year floods, meaning the country should be shielded from the worst disaster that could be expected over the course of 10,000 years. But climate change is forcing the Dutch to alter their calculations and fortify their protections. Globally, sea levels have already risen by nearly 30 cm over the past century, a rate that is accelerating, and as the globe continues to warm, the Dutch are preparing their country to deal with a 1.3 m rise in the North Sea by 2100. The cost will be high — well over $1 billion a year to heighten seawalls, on top of the $500 million a year the Dutch spend just to keep the Delta Works system running. But the alternative would be to leave their cities unprotected from the higher seas and stronger storms expected in a warmer world.

That grim alternative was on full display in New York City in the aftermath of Superstorm Sandy. Storm surges in lower Manhattan reached 4.25 m, shattering a nearly 200-year-old record. The resulting floods inundated cars and buildings, knocked the city's vital subways out of commission and left hundreds of thousands of New Yorkers without power. In the coastal communities of Queens and Staten Island, beyond the dense core of lower Manhattan, the damage was even greater, with more than 40 New Yorkers dying in the storm and its aftermath. Altogether, the bill from Sandy — which affected U.S. states from North Carolina to Rhode Island — is likely to be well north of $50 billion. And New York City, home to the greatest concentration of wealth in the world, will never be the same.

There's no way to know just how much man-made climate change might have amplified Sandy. But city planners in New York should have known enough to provide greater protection for the homes, businesses and vital infrastructure built close to a rising sea. That may change in the future, as New York Governor Andrew Cuomo pointed out after Sandy struck. "Climate change is a reality," Cuomo said. "Given the frequency of these extreme weather situations we have had, for us to sit here and say this is once in a generation and is not going to happen again, I think would be shortsighted."

New York may be the most recent coastal city to become the victim of a climate-torqued natural disaster, but it's hardly the only metropolis in danger. A 2007 report by the Organisation for Economic Co-operation and Development found that 40 million people — and $3 trillion in assets — live in cities that could be exposed to major 1-in-100-year coastal-flood events, in metropolises like Shanghai, Miami and Mumbai. As these cities boom, so does their vulnerability — the same report estimates that by 2070, 150 million people and $35 trillion in assets could be exposed to major coastal floods. Even if global warming turns out to be less threatening than most climate scientists fear, there will be more people and more expensive property in harm's way of coastal floods over the years to come. Worse, most of that growth will take place in developing nations that may lack the resources to adapt to climate change.

That sets the stage not just for a human disaster but also potentially for an economic one that could be felt well beyond the site of the catastrophe. Severe floods struck the Thai capital of Bangkok in 2011, inundating the factories that churn out as much as a quarter of the world's disk drives. The floods cost Thailand nearly $50 billion, but the disaster also disrupted global supply chains, leading to a worldwide shortage. "As global corporations expand into emerging growth markets, their operations and supply chains will become exposed to a complex set of climate risks," said Helen Hodge, head of maps and indices at the risk-research firm Maplecroft, which recently published an urban climate vulnerability index. The lesson for cities and corporations is clear: prepare for climate change or risk turning a natural disaster into man-made catastrophe.

Dutch cities like Amsterdam and Rotterdam aren't the only examples of urban areas that have taken real — if expensive — steps to shore up against the effects of global warming. Like many old cities, London was built on a floodplain and was victimized by storm surges repeatedly throughout its history — including the 1953 Watersnoodramp. That flood persuaded British officials to begin building the great Thames Barrier, the second largest movable seawall in the world after the Delta Works. Finally completed in 1984 at the cost of more than $2 billion in today's figures, the Thames Barrier is usually open to allow maritime traffic down one of the world's busiest rivers. But the gates swing shut to protect London from a rising storm surge — a maneuver that has been required more than 100 times since the barrier was completed. The half-drowned Italian city of Venice — which has to contend with rising sea levels even as it sinks at the rate of nearly 4 cm a century — is building the multibillion-dollar MOSE project, a network of seawalls meant to close off the city from surging tides.

In the weeks since Sandy, New York officials have been debating the wisdom of installing similar seawalls to protect Manhattan. (While New York City has more than 800 km of coastline, it has few physical defenses against flooding.) But most of the plans being considered would cost more than $10 billion, take years to complete and leave people and property beyond the seawalls at even greater risk of flooding. As the failure of the levees in New Orleans after Hurricane Katrina showed, physical barriers don't guarantee safety — especially as climate change raises sea levels beyond what cities had prepared for. (The Thames Barrier will likely be outpaced by rising seas as soon as 2050.) "I don't think there's a practical way to build barriers in the ocean," New York Mayor Michael Bloomberg said after Sandy hit. "If you spent a fortune, it's not clear to me that you would get much value for it."

Even the Netherlands is moving away from a coastal-defense system based only on expensive seawalls. The Dutch are investing in a plan called Room for Rivers, which uses sandbars to give waterways the space to overflow safely during floods. For the developing-world cities that are more vulnerable to climate change, such as Kolkata or Ho Chi Minh City, multibillion-dollar seawalls will likely never be a viable option. But there are alternatives. The Bangladeshi capital of Dhaka — a constant victim of floods and cyclones — has been building embankments, concrete-reinforced walls and pumping stations in the most densely populated parts of the city. Emergency shelters are built on stilts so that residents have a safe place to gather in the event of a storm. Bangladeshis have even adapted to the frequent floods by creating biaras — floating fruit-and-vegetable gardens that rise and fall with the water level. Still, no one thinks those small adaptations alone will save Dhaka, which Maplecroft rated this month as the global city most vulnerable to climate change.

It doesn't help that Dhaka's development has stripped away the wetlands and mangrove forests that can provide a natural barrier to storm surges, even as more and more people have piled into coastal danger zones. It's a mistake that has been repeated in rich and poor cities around the world. In the U.S., nearly 4 million people live within a meter of high tide, putting them at risk every time a storm whips by. Globally, more than 600 million people live in cities and towns less than 10 m above sea level. When storms and floods do strike — and they'll likely become worse with warming — they affect more people and more property. Cities like Amsterdam, London and Venice have proved that it is possible to fight rising seas and coastal floods — albeit at a stiff price. But unless we deal directly with climate change, the sea will one day win out.