Shanghai has sunk by nearly three meters over the past 80 years, causing 14.5 billion yuan (US$1.7 billion) worth of damage, according to a report issued by the Nanjing Geological Survey Center. Sixteen provinces and regions and 46 major cities also suffer from subsidence.

Researchers believe that excessive pumping of underground water the primary cause of the problem.

The report, with contributions from the geological departments of Jiangsu and Zhejiang provinces and Shanghai Municipality, shows that land south of the Yangtze River has sunk by an average of more than 20 centimeters over an area of almost 10,000 square kilometers.

The most serious ground subsidence occurs in the urban districts of Shanghai Municipality and Suzhou, Wuxi and Changzhou in east China's Jiangsu Province, and Jiaxing in Zhejiang Province. Subsidence in these areas has reached as much as 2.6 meters.

Suzhou, Wuxi and Changzhou have lost 2.6 billion yuan (US$310 million) because of the problem, which affects both urban and rural areas. It causes damage to buildings and problems such as flooding on farmland.

Guo Kunyi, vice director of the Nanjing Geological Survey Center and the person in charge of the report, said that underground water should be pumped with restrictions. He says that replacing underground water could prevent further subsidence.

The government should also invest in monitoring machines and survey equipment, Guo added. Most evidence of problems underground comes from cracks and subsidence. Timely checking of such evidence and prompt response can prevent further subsidence before it is too late.

The researchers worked nearly five years on the report, which cost more than 40 million yuan (US$4.8 million) to complete.

(China Daily March 22, 2005)