By Cleo Pascal

Superstorm Sandy brought devastation to New York and the city is still cleaning up the mess. When disasters hit big cities, the media naturally focus on human tragedies. In the heart-rending chaos, large, systemic failures get brief mention.

However, as patterns develop over time, it is becoming clear that those systemic failures are occurring more often. One increasingly glaring problem is that many global trade and financial centres, including Shanghai, Mumbai, Bangkok, London as well as New York, are in vulnerable locations. Each city is projected to be increasingly subject to extreme weather, throwing periodic wrenches into the global economy. Such disruptions can weaken economic systems, and have unexpected cascading effects, from shutting down trading floors, to rupturing critical supply chains.

Extreme weather is just one factor, however. Most financial centres grew up around ports which placed these cities on the coast -- New York, Shanghai, Mumbai, Bangkok -- or, like London, on a large river. Population booms then led to haphazard zoning and development.

The result is overstretched infrastructure papering over the cracks in an increasingly unstable environment. Buildings start subsiding, airports go up on floodplains, saltwater infiltrates underground wiring and transport systems. And the city -- a critical hub in a global economy -- becomes a disaster waiting to happen. In future there will be more Sandys hitting more global centres more often. And they will affect you. Here we look at five cities and the threat they face from just one disruption, flooding.

New York

The greater Manhattan area has a combined estimated population of

22 million, an economy of at least $1 trillion, and built assets worth $2 trillion. Much of its critical infrastructure is

3 metres above sea level. That doesn't mean it takes a 3 metre rise in sea level for there to be a problem. All it takes is a storm surge. In 2011, Hurricane Irene whipped up a 1.2 metre surge, and caused more than $15 billion in damage. In November, Sandy brought over a 4 metre surge, and shut down energy and water systems, airports, tunnels, subways, highways, and the New York Stock Exchange. In an era in which high-frequency trading means companies are willing to pay extra to be a few feet closer to the trading floor, whole sections of the city were closed down. Much of the southern tip of Manhattan is on reclaimed land, and particularly low lying. This will happen again.

Average elevation about 30 metres for Manhattan, but much critical infrastructure, especially at the southern tip, is less than 3 metres above sea level.

Estimated population at risk (millions): 1.9

Shanghai

The journal Natural Hazards this year declared Shanghai as the major city 'most vulnerable to flood risks'. Shanghai means on the sea. China's glittering economic showpiece is, like New Orleans, at the mouth of a delta, and in a typhoon pathway. Also like New Orleans, sections of it are subsiding, and haphazard development has resulted in building on flood plains, draining wetlands, moving waterways, all undermining its stability. A direct typhoon hit on Shanghai could have an enormous effect on the global economy if China decides to use its foreign exchange holdings to pay for a massive rebuild. It could also affect security if one of the myriad chemical plants in and around the city is breached, creating a 'chemical Fukushima'.

Average elevation above sea level: 3 metres.

Estimated population at risk (millions): 2.3

Mumbai

Mumbai is the throbbing business and entertainment capital of India. The heart of the city was made up of seven islands that, over time, were merged through land reclamation. Its low elevation combined with booming unregulated housing in flood zones, poor drainage, and increasingly erratic and extreme rains, explain why the city is facing serious challenges. In 2005, severe floods killed thousands and shut down the city, including much of the banking sector. As Mumbai is a regional hub and outsourcing centre, the effects rippled out globally. Little has been done since to reinforce its infrastructure.

Average elevation: 15 metres, but much critical infrastructure, especially in the heart of the city, is just about sea level.

Estimated population at risk (millions): 3

Bangkok

Bangkok is the delta megacity, with an estimated population of 14 million, and an average elevation of around 1.8 metres -- though parts are actually below sea level. Once known as the Venice of the East, it is suffering serious subsidence. During the 1980s, in some places, Bangkok was sinking by more than 12 centimetres a year. That rate has declined but the city is still highly exposed. While not a global financial centre, Bangkok is an important manufacturing base and port. Thailand's 2011 floods were among the most costly in history, causing an estimated $45 billion in damage and affecting global supply chains, including a worldwide shortage in hard disk drives. Production for Honda, Nissan and Sony, among others was badly hit.

Average elevation above sea level: 1.5 metres.

Estimated population at risk (millions): 1

London

The world's leading financial centre cannot count on the Thames Barrier to keep it dry. There are five ways London could flood: tidal surges can drive seawater up the Thames; swollen rivers can send swells down it; heavy rains can overwhelm drainage systems; sewers can back up; and groundwater can rise. The Thames Barrier is designed to stop tidal surges but only until 2030. According to the Greater London Authority's London Climate Change Adaptation Strategy,

'a significant proportion of London's critical infrastructure is at risk of flooding, including emergency services and utilities that London would be reliant upon in case of a flood'.

The British Government's Flood and Coastal Defence report summed up the situation: 'Hard choices need to be taken -- we must either invest more in sustainable approaches to flood and coastal management or learn to live with increased flooding.'

An estimated 15 per cent of London lies on river flood plains.

Estimated population at risk (millions): 1.4

 

Cleo Pascal is an Associate Fellow, Energy, Environment and Resources, Chatham House and author of 'Global Warring'

 

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