Magnitude and Extent of Six Years of Land Subsidence in Shanghai Revealed by JERS-1 SAR Data 477 Magnitude and Extent of Six Years of Land Subsidence in Shanghai Revealed by JERS-1 SAR Data

Many provinces in China including Shanghai, Tianjin, Jiansu, Hubei, Hangzhou, Suzhou, Changzhou, Cangzhou, and Jianxing (Deng and Ju, 1994; Ding et al., 2005; Hu et al., 2004; Xue et al., 2005; Yang et al., 2005) are subsiding owing to rapid development and urbanization. The cause identified with these subsidence phenomena has been mainly due to excessive withdrawal of groundwater (Chai et al., 2004; Shi and Bao, 1984; Xue et al., 2005; Yang et al., 2005). The subsidence phenomenon in China occurs mostly in medium-seized and large cities with common characteristics of being slow, accumulative and irreversible (Xue et al., 2005). At least, 45 cities and municipalities (China Daily, 2003b; Deng and Ju, 1994; Hu et al., 2004) are experiencing this geological problem owing to massive exploitation of underground water to meet the needs of the rapid evolving industries and urbanisation. In the case of Shanghai, the massive construction of high-rise buildings in the downtown area has also contributed to the subsidence problem (China Daily, 2003b; Zhang et al., 2002). About 11 cities, including Shanghai, have recorded accumulative subsidence values exceeding 1 m at their subsidence centres (Hu et al., 2004; Yang et al., 2005; Zhang et al., 2002). The most affected cities, since the early 1900s, are Shanghai, Tianjin and Taiyuan, with each of them having accumulative subsidence value greater than 2m (China Daily, 2003b). The Chinese government has spent billions of Yuan (RMB$), as direct and indirect economic costs, in addressing land subsidence problems in China. Hu et al. (2004) mentioned that the estimated total economic loss due to land subsidence in Tianjin is RMB$189.6 billion. In the three areas of Suzhou, Wuxi and Changzhou, the total economic loss is estimated at RMB$46.87 billion (Yang et al., 2005). For Shanghai, the China Daily (2003b) and Yang et al. (2005) quoted the total economic losses of about RMB$290 billion, in the last 40 years, due to land subsidence and its related problems. 25