The Hong Kong Observatory (HKO) announced Monday that the mean sea level in the Victoria Harbor has risen by 0.12 meter during the past 50 years.

According to the result of a study on long term sea level in Hong Kong conveyed by HKO, during the past 50 years, the mean sea level in the Victoria Harbor has been rising at an average rate of 2.3 millimeters per year. For Tolo Harbor, the mean sea level has also risen by 0.12 meter in the last 40 years, at an average rate of 3 millimeters per year.

Due to tides and meteorological effects, the sea level is in a continuously changing state. Ocean currents of the South China Sea, fresh water discharge and sedimentation from the Pearl River, as well as changes in coastline due to large scale reclamation affect the sea currents and sea levels at various parts of Hong Kong waters, said the Assistant Director of the HKO Yeung Kai-hing.

The highest sea levels in Hong Kong have been caused by storm surges associated with typhoons. "Near the center of a typhoon, the sea surface bulges upward as the atmospheric pressure is lower than that of the exterior. The strong winds associated with a typhoon will also drag and pile water up towards the coast and bring sea flooding to coastal low lying areas," explained Yeung.

Sea flooding due to storm surges is not common in Hong Kong and as the effects of storm surges and long term sea level rise have been taken into consideration in the design of coastal projects, it is unlikely that the sea level will pose a threat to Hong Kong in the near future.

The Hong Kong Observatory's study also reveals that the inter-annual change in the sea level in Victoria Harbor was particularly prominent in the past 15 years, with steep rise of the annual mean sea level from 1987 to 1999 and rapid fall after that. This period coincides with the most rapid rise in the global average temperatures since instrumental measurement of air temperatures began in the 1860s. This suggests that global warming might be an important factor in the sea level change in Hong Kong.

Yeung said that Regional climate change study is a key area of work of the HKO and in cooperation with the Lands Department and Hong Kong Polytechnic University, it has started to make measurement of the vertical ground movement at tide gauge stations, using satellite-based Global Positioning System techniques, since 2004. The data will support long term sea level change studies in future.

(Xinhua News Agency June 15, 2004)