Tide gauge records in the Victoria Harbour since 1954 demonstrate an unambiguous rise of the mean sea level during this period. There was a rapid rise of the sea level from 1990 to 1999 and a moderate decline thereafter. The trend is similar to that observed by satellite remote sensing over the South China Sea since the early 1990s and also tide gauge records at other coastal stations in the region. On average, the mean sea level in the Victoria Harbour has risen at a rate of 2.8 mm per year during the period 1954 to 2011.

Annual mean sea level at Victoria Harbour (1954-2011)

A major impact of the mean sea level rise in Hong Kong is an increase in sea flooding from storm surges caused by tropical cyclones. For a rise of 0.18 m or 0.59 m in the mean sea level and assuming no change in storm characteristics, the extreme sea levels in the Victoria Harbour for various return periods would become higher as illustrated below:

Return Period (years)	Extreme sea level above Chart Datum (m)
	Current mean sea level	A rise of 0.18 m in mean sea level	A rise of 0.59 m in mean sea level
2	2.9	3.1	3.5
5	3.1	3.3	3.7
10	3.3	3.4	3.8
20	3.4	3.6	4.0
50	3.6	3.7	4.1
100	3.7	3.9	4.3
200	3.8	4.0	4.4

        Note: Chart Datum is 0.146 metre below Principal Datum.