Sea levels rising at an "alarming" rate because of climate change and depleting groundwater threaten coastal economies, officials warned Tuesday.
Two key cities, Shanghai and Tianjin, are among those facing the biggest threat, State Oceanic Administration (SOA) spokesman Li Haiqing said, citing the agency's 2007 sea-level monitoring report.
In the last 30 years, the financial hub of Shanghai has seen the sea level rise 115 mm, or the length of half a chopstick, the report says.
Tianjin, a major port about two hours' drive from Beijing, has seen the level rise as much as 196 mm, about the length of a new pencil.
In the past 30 years, the country's overall sea level has risen 90 mm with the average offshore surface temperature going up by 0.9C.
In comparison, when the global sea level rose 1.7 mm every year between 1975 and 2007, the Chinese sea level rose 2.5 mm every year, the SOA reports.
In the next decade, the SOA forecasts, China's coastal sea level is likely to rise by 32 mm, or 3.2 mm every year.
This is the first time the SOA has reported the cumulative figures of sea level rises in the last 30 years. The report is now being released annually, instead of every three years.
A three-degree risk rating system is being set up by the SOA to inform coastal cities of potential threats they face, Chen Manchun, a researcher with the SOA, told China Daily.
Sea level rises worldwide cannot be reversed, so Chinese city officials and planners must take measures to adapt to the change, he said.
Global warming is the main reason for the rising sea levels, SOA officials said, but surface subsidence is also to blame for the threat of floods in Shanghai and Tianjin - due to their "indiscriminate exploitation of groundwater resources" - Chen said.
Shanghai is also facing additional trouble in ensuring fresh water supply to its 20 million residents due to seawater intrusion, he pointed out.
The sea level report also shows an imbalance, the SOA reported without explaining the reason. From the Yangtze River Delta to the north, cities tend to face more serious problems than those in the south.
Liaoning, Shandong and Zhejiang provinces saw sea levels rise about 100 mm, while in Fujian and Guangdong provinces, including the area about the Pearl River Delta and Hong Kong, the rise was 50-60 mm.
Also Tuesday, the SOA released its China 2007 Sea Environmental Quality Report and China 2007 Sea Disaster Report. The environmental quality report shows serious deterioration in offshore water quality caused by pollution from onshore sources.