Shanghai is Sinking

The only thing keeping the Huangpu River out of the Peace Hotel’s Art Deco lobby on Shanghai’s waterfront this summer is a concrete flood wall.

It’s not that the river has risen more than usual during the rainy season. Instead, Shanghai is sinking.

The land under the skyscrapers and 13 million people of this bustling metropolis is deflating like a giant air mattress, slowly settling as its shallow water table collapses after decades of overuse.

Sinking Widespread

Sinking cities are common in chronically dry China, which is guzzling water from underground aquifers to supply a booming economy and growing population.

Land under 46 cities is sinking, the government says. Areas around Beijing, the capital, have sunk by up to 14 inches over the past decade.

Although Chinese officials warn publicly about relying too heavily on wells, drought in recent years has complicated their efforts. As rivers dry up, cities and farms drill more wells. More than 100 cities in northern China are short of water, the official Xinhua News Agency has reported. Some reservoirs are dry.

Shanghai has switched to river water for most uses, slowing its annual descent to less than two-fifths of an inch. But after years of rapid decline, even that threatens China’s business capital, which sprawls across flat land less than 10 feet above the Huangpu.

“If we didn’t control this, the ground would collapse” by three feet every decade, said Liu Yi, a government geologist who tracks the sinking. “The damage would be unbelievable — floods and wrecked buildings.”

Drained Water

Shanghai, one of the world’s most densely populated cities, switched fairly easily to water from the Huangpu and Yangtze rivers. But it still suffers the legacy of long, severe bouts of ground subsidence.

The problem stems from Shanghai’s rapid 19th century metamorphosis into a foreign colonial base. Shallow aquifers that had supported a Chinese trading port were quickly strained supplying factories and a populace that tripled by 1900 to more than 1 million.

The sinking was first noticed in 1921, but Shanghai went on using ground water for decades, according to Liu, the senior geologist for the Shanghai Institute of Geological Survey. The problem got so bad by the 1950s and 1960s that the ground was sinking by four inches a year.

The government took action in 1963, banning most wells and limiting use of the rest. Still the decline continued, and Liu said that since the mid-1960s the city has settled 16 more inches.

Shanghai has avoided nightmare scenarios of flooding in urban neighborhoods or among the office towers of its sleek new financial district. But official projections say water levels could rise 19 to 27 inches by 2050, threatening waterfront areas.

Downtown Flood Wall

Worst-hit is the old city center, where sections are at or below the Huangpu’s level. The district has some of Shanghai’s most valuable real estate and the Bund, the former British settlement whose 1920s-era buildings make up the city’s signature skyline.

The Bund’s name comes from Hindi — a reminder of British colonial rule in India — and means embankment. The Huangpu then was low enough that its flat bank was used as a mule path to tow junks up the river.

That bank is now topped by a flood wall built in the early 1990s by city leaders worried that the summertime Huangpu would overflow onto Sun Yat-sen Road, the eight-lane riverfront boulevard.

They concealed the menace with Shanghainese flair, filling the wall with shops and topping it with a tourist promenade. Families stroll the wide walkway on summer evenings, unruffled that the water on one side is higher than the ground on the other.

Even before its mid-August peak, the Huangpu already is level with the road, said Zhang Liugang, an official of the city Anti-Flood Office. In 1997, he said, the rain-gorged river ran five feet higher than the road and came within 3½ feet of the top of the flood wall.

Reversing Nature’s Flow

The geologist Liu has spent 12 years tracking the city’s decline. His staff of 100 and network of 27 monitoring stations with sensors drilled 300 to 600 feet into the earth monitor the shifts.

“You can’t see it if you look around, but the problem is terrible. We can’t wait until it’s visible,” Liu said.

In a tactic that borders on science fiction, Shanghai is trying to reverse the decline by recharging its aquifers, pumping in 5.2 billion gallons of water a year.

The program, Liu said, has met with modest success, with land in some areas rising as much as 4½ inches.