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climate change

Observed Climate Change in Hong Kong

Mean sea level


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 and that recorded by tide gauges at other coastal stations in the region. On average, the mean sea level in the Victoria Harbour rose at a rate of 29 mm per decade during the period 1954 to 2013.

annual mean sea level at Victoria Harbour from 1954 to 2013

Annual mean sea level at Victoria Harbour (1954-2013)

In connection with mean sea level rise as a result of climate change, a major impact in Hong Kong is an increase in sea flooding associated with storm surges caused by tropical cyclones. The extreme sea level brought by storm surges of the same typhoon will be higher when the mean sea level is raised (see diagrams below).

diagrams

Based on the IPCC Fifth Assessment Report (AR5), for a mean sea level rise reaching 0.38 m in mid-21st century (2046-2065) and reaching 0.82 m in late 21st century (2081-2100) under the RCP8.5 scenario with the highest concentration of greenhouse gas emission, and assuming no change in storm characteristics, the return periods for various extreme sea levels in the Victoria Harbour will shorten as shown in the table below, meaning that the frequency of occurrence of a particular extreme sea level will increase.

Return period
(Year)

Extreme sea level above Chart Datum#(m)
Current
mean sea level
For a sea level rise
reaching 0.38m in the
mid 21st century
(2046-2065)
For a sea level rise
reaching 0.82m in the
late 21st century
(2081-2100)
1 2.7 3.1 3.5
2 2.9 3.3 3.7
5 3.1 3.5 3.9
10 3.3 3.6 4.1
20 3.4 3.8 4.2
50 3.5 3.9 4.4

#Chart Datum is the level to which soundings or tide heights are referenced, and is approximately the level of lowest astronomical tide in the Victoria Harbour. Chart Datum is 0.146 m below the Hong Kong Principal Datum, the level to which land surveys in Hong Kong are referenced.

Using the example of an extreme sea level of 3.53 m in the Victoria Harbour brought by Typhoon Hagupit in 2008, its return period will shorten from around 50 years at present to around 5 years in mid-21st century (2046-2065), and even every year by late 21st century (2081-2100).

 

 

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Last revision date: <17 Mar 2014>