Long-term sea-level changes in Hong Kong from tide-gauge records

Over four decades of tide-gauge data and leveling measurements collected at two tide-gauge stations in Hong Kong are analyzed to study the long-term tendency and the frequency features in the sea-level changes in the region. The results show that there has been a long-term sea-level rise of 1.9 mm per year and a land subsidence of over 4 mm per year at the tide-gauge stations. The variations in sea-level from seasonal through to decadal time scales are detected by using the time-frequency spectrum of wavelet transform. The annual, semiannual and the 18.6-year variations are most significant and exhibit stable periodicity. The local atmospheric pressure variations mainly influence the annual sea-level change and the effect amounts to 33% of the magnitude calculated before the inverted barometer corrections are applied. It is also projected from the extrapolation of the current trends of sea-level rise and ground subsidence that the absolute and relative mean sea-levels in Hong Kong may further rise by 10 cm and 30 cm respectively by the middle of the next century. The possible maximum relative mean sea-level change, when considering the various temporal variations, can be as high as 50 cm in the next half century.