Many parts of the mainland are sinking because of rapid
urbanization and heavy use of underground water, a study conducted
by the Chinese University of Hong Kong found.
Researchers projected that coastal cities like Shanghai subsided
by 5 to 7 millimeters each year and would become unsuitable for
human living in 100 years.
The university's Institute of Space and Earth Information
Science found that urbanization had created immense pressure on the
ecology and human living environment in China.
The urbanization rate in Dongguan city has increased from 13
percent in 1979 to 51 percent in 2000. Shenzhen is housing more
than 10 million people on its less than 2,000 square kilometers of
land, with an annual population growth rate of 15 percent from 1990
to 2000.
The trend created surging demands for housing, infrastructure
and energy, the study said.
The institute assistant professor, Zhang Yuanzhi said
urbanization would result in the constructing of surfaces which
were impervious to water on the ground, such as asphalt and
concrete roads. Increased prevalence of impervious surfaces would
lead to a higher pressure in drainage and flood prevention of the
cities, especially during heavy rains.
Underground water was also pumped away to fulfill the higher
demand for drinking water, Zhang said. Combined with the effect
caused by impervious surfaces, land subsidence would result.
Zhang said some 50,000 square kilometers of lands in 96 cities
of the nation were subsiding. About 80 percent of these subsided
lands were along the eastern seaboard. The situation was more
serious in the Yangtze River Delta and the Bohai-Tianjin
Region.
Underground water in some cities, such as Datong in Shanxi
province, was pumped away for use in power plants. Mining in
Luoyang also contributed to the problem.
"It is projected that the land subsidence is ranged from 5 to 10
millimeters a year. That figure superficially appears
insignificant. But serious problem will result in a longer period,"
Zhang said, adding that some cities would not be suitable for human
activities after the land subsidence.
The impervious surfaces also replaced the vegetated lands,
making it more difficult for heat to be dispersed by plants.
The heat island effect would be more serious, Zhang said.
The study found that the impervious surfaces percentage for
urban areas in Kowloon and Hong Kong Island had reached 60 percent
or above. The percentage for the SAR's countryside was below 40
percent.
However, the land subsidence in Hong Kong was stable, he
said.
Zhang said the pace of urbanization should be slowed down, and
the building intensity should be reduced.
The over-use of underground water on the mainland should be
restricted, he said.
"Measures should be taken to slow down the land subsidence," he
added.
(China Daily HK Edition August 7, 2007)
