Subsidence has become a topic often bemoaned in China and as of today, this plague is far from reaching its end. More than 70 cities in china have different subsidence problems, covering a total area of 64,000 sq kilometers.

Shanghai is the city most seriously affected, with the deepest settlement at 2.6 meters. Since subsidence was first identified in 1921, Shanghai has seen direct economic losses of one trillion yuan.

Underground water systems have been destroyed in some of north China's cities, while water quality has frequently been affected by the issue. In Xi'an, where famous architecture dates back to Tang Dynasty, the Big Wild Goose Pagoda, has tilted thousand millimeters due to surface subsidence.

Other cities, like Tianjin, Taiyuan and Suzhou, are also tortured by such problems.

Heavy use of local groundwater and excessive urban construction are cited as the reason for subsidence. Consequentially, many cities hit by subsidence have substantially reduced groundwater extraction. In Suzhou, Wuxi and Changzhou in eastern China, underwater extraction dropped to 3 million cubic meters from 290 million in 2000. The annual rate of subsidence has been controlled at below 25 millimeters per year in the three cities, with no terra crack disasters occurring in the cities since 2003.

One scholar from Chinese Academy of Science, Lin Xueyu suggests that, "the settlement is degenerative and undetectable. Its monitoring is therefore equally important and difficult."

A Subsidence monitoring project has recently been approved in eastern China's Jiangshu Province. With 249 GPS points located along the Yangtze River, the monitoring system has played an important role in subsidence prevention.

(CRI February 14, 2007)