Rising seas threaten Shanghai, other big cities

updated 3:31 p.m. ET Oct. 18, 2009

EDITOR'S NOTE — This is one of an occasional series of stories leading up to December's climate conference in Copenhagen, reporting on the impact, future and responses to climate change

SHANGHAI - 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 and other weather-related catastrophes.

Shanghai, altitude roughly 3 meters (10 feet) 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, expanding from warmth and meltwater. Estimates of the scale and timing vary, but Stefan Rahmstorf, a respected expert at Germany's Potsdam Institute, expects a 1-meter (3-foot) rise in this century and up to 5 meters (15 feet) over the next 300 years.

Chinese cities are among the largest and 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.

Sea is advancing
The sea is steadily advancing on Shanghai, tainting its freshwater supplies as it turns coastal land and groundwater salty, slowing drainage of the area's heavily polluted flood basin and eating away at the precious delta soils that form the city's foundations.

Planners are slow in addressing the threat, in the apparent belief they have time. Instead, Shanghai has thrown its energies into constructing billions of dollars worth of new infrastructure: new ports, bridges, airports, industrial zones, right on the coast.

"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. In modern times, the city has been sinking for decades, thanks to pumping of groundwater and the construction of thousands of high-rise buildings.

Reinforcing flood gates and levees
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 (330-foot-wide) 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 (19-foot) 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 (nearly 19 feet), during a 1997 typhoon.

Levees along the Bund and other major waterways are 6.9 meters (nearly 23 feet) 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 (28-foot) 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 (18 miles) downstream where the deep, muddy Huangpu empties into the Yangtze.

‘It is extremely complicated’
Sang Baoliang, deputy director of the Shanghai Flood Control Headquarters, has been to see the Thames Barrier, which protects London, and the Deltaworks series of storm barriers and dams in the Netherlands, where two-thirds of the population lives on land below sea level, much of it reclaimed from the sea.

Like many Chinese officials, some of whom deem the topic too sensitive to discuss, Sang is cautious about what China might do.

"We are studying this, but it is extremely complicated," said Sang, as shots from surveillance cameras at dozens of flood gates flashed on a full-wall screen.

"If the research determines that indeed the sea level will rise further, then we will need to build the walls higher. But this is still under research," he said.

Such projects usually require several decades of planning and construction, and with sea levels rising, they likely will have to be adjusted, given the unknowns of climate change.

"Nobody — no municipal or provincial government, and no central government agency — is preparing adaptation plans for Shanghai or the Yangtze Delta," says Edward Leman, whose Ottawa-based consultancy Chreod Ltd. has published research on the issue. "They must begin now, as investments and decisions made today will have a major impact in the coming years."

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