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October 21, 2009

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Home » Opinion » Foreign Views

World's major cities menaced by rising tide

By Elaine Kurtenbach | October 21, 2009, Wednesday | Print Edition

THIS city of 20 million rose from the sea and grew into a modern showcase, with skyscrapers piercing the clouds, atop tidal flats fed by the mighty Yangtze River.

Now Shanghai's future depends on finding ways to prevent the same waters from reclaiming it. Global warming and melting glaciers and polar ice sheets are raising sea levels worldwide, leaving tens of millions of people in coastal areas and on low-lying islands vulnerable to flooding.

Shanghai, altitude roughly three meters above sea level, is among dozens of great world cities - including London, Miami, New York, New Orleans, Mumbai, Cairo, Amsterdam and Tokyo - threatened by sea levels that now are rising twice as fast as projected just a few years ago.

Estimates of the scale and timing vary, but Stefan Rahmstorf, a respected expert at Germany's Potsdam Institute, expects a one-meter rise in this century and up to five meters over the next 300 years.

Chinese cities are among the most threatened. Their huge populations - the Yangtze River Delta region alone has about 80 million people - and their rapid growth into giant industrial, financial and shipping centers could mean massive losses from rising sea levels, experts say.

Many planners are slow in addressing the threat, in the apparent belief they have time. "By no means will Shanghai be under the sea 50 years from now. It won't be like the 'Day After Tomorrow' scenario," says Zheng Hongbo, a geologist who heads the School of Earth Science and Engineering at Nanjing University.

"Scientifically, though, this is a problem whether we like it or not," says Zheng, pointing to areas along Shanghai's coast thought to be shrinking due to erosion caused by rising water levels.

Chinese legend credits Emperor Yu the Great with taming floods in Neolithic times by dredging new river channels to absorb excess water. Today, Shanghai's engineers are reinforcing flood gates and levees to contain rivers rising due to heavy silting and subsidence.

"We used to play on the river banks and swim in the water when I was growing up. But the river is higher now," says Ma Shikang, an engineer overseeing Shanghai's main flood gate, pointing to homes below water level near the city's famed riverfront Bund.

Twice daily, the 100-meter barrier, where the city's Suzhou Creek empties into the Huangpu River, is raised and lowered in tandem with the tides and weather, regulating the city's vast labyrinth of canals and creeks.

The 5.86-meter high flood gate is built to withstand a one-in-1,000 years tidal surge; the highest modern Shanghai has faced so far was 5.72 meters, during a 1997 typhoon.

Levees along the Bund and other major waterways are 6.9 meters high, providing better protection than in Miami, New York and many other cities. But they still would be swamped if hit by a surge like Hurricane Katrina's 8.5-meter onslaught.

Shanghai is considering building still bigger barriers - like those in London, Venice and the Netherlands - to fend off potentially disastrous storm surges, most likely at the point 30 kilometers downstream where the deep, muddy Huangpu empties into the Yangtze.

Nearly a quarter of mankind lives in low-lying coastal areas, and urbanization is drawing still more people into them.

"The tendency of coastal and port locations to become playgrounds for architects and developers has become a global phenomenon in recent decades," says Gordon McGranahan, director of the human settlements group at the International Institute for Environment and Development, an independent think tank in London.

McGranahan helped author a 2007 report by the Organization of Economic Cooperation and Development that put the number of people living in areas vulnerable to such flooding at 40 million people, with trillions of dollars of homes and other assets at risk. By the 2070s, the number could rise to nearly 150 million, it says.

Extreme weather will aggravate the already precarious situation for many: in September, Tropical Storm Kestana left 80 percent of the Philippine capital, Manila, under water.

In years to come, some Pacific islands, like tiny Tuvalu, are expecting complete inundation. Vietnam's environment ministry estimates that more than a third of the Mekong Delta, where nearly half the country's rice is grown, will be submerged if sea levels rise by one meter.

Bangladesh is spending billions of dollars on dikes and storm shelters, while seeking international aid to help it adapt to flooding that could force up to 35 million of its people to relocate by 2050.

Though much of its land is arid, China likewise has millions of people living in densely populated tidal flats and coastal valleys who already must be evacuated during typhoons. Many of the country's biggest cities are threatened, the OECD report says.

"What has been specific to China has been the enormous coastward migration, unfortunately just at a time when it would have been better not to settle low-elevation coastal areas," McGranahan said.

Traces of former sea walls show that much of today's Shanghai, which sits between a flood basin and the sea, was under water or marshland until the 7th or 8th century AD. Over thousands of years, ancient settlements expanded and withdrew as water levels ebbed and rose.

In the future, communities unable to move may instead end up adapting buildings and infrastructure to accommodate higher water levels, says Hui-Li Lee, a landscape architect who is working on several projects in the region.

"There are many things we cannot account for, but if we know an area is going to flood, we have to plan for that," Lee said. "When we look at a map, we have to think that 30 years or 50 years later everything will be below sea level."

Foreign Views


 

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