If you visit Shanghai and get a sinking feeling, you're on to something. China's most populous coastal city has had a subsidence problem for decades. This was due, first, to its swampy terrain. Second, there was too much pumping of groundwater. City officials successfully waged a determined effort to replenish depleted aquifers with treated water; they also placed tough restrictions on the use of groundwater. But now, the sinking has returned with a vengeance - at a rate of around 7 millimeters a year. This time, the cause is the city's high-rise building boom, one key result of Shanghai's transformation into a global financial center.

Researchers believe that improved technology may help limit the damage: deeper basements to offset building weight and arrays of piles to relieve pressure. But subsidence isn't Shanghai's only construction-related problem. Last year, the Shanghai Daily reported that, based on samples taken by the city's Industrial and Commercial Administrative Bureau, half the steel sold wholesale to construction companies was lighter than the legal standard, and a quarter flunked tension tests.

And a future scare looms: Researchers say Shanghai is among cities vulnerable to rising sea levels caused by global warming. -TG

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