Storm surge hazard in Hong Kong under global climate changes

Abstract

The impact of Typhoon Hagupit has raised public awareness on the hazard of storm surge. The international research and local tide gauge data collected over the years, has shown the trend on sea level rise. From the tropical cyclones and storm surge database of the Hong Kong Observatory, a study on the trends of storm surge impacting Hong Kong (1960~2008) has been carried out to investigate whether significant changes of extreme sea level have taken place under climate changes.

The mechanism of storm surge is described in the beginning of this dissertation, followed by clarification of the methods and data used for analysis. It was found that a significant sea level rise was recorded in both Victoria Harbor and Tai Po Kau in the past half century. However, the annual extreme sea level and maximum storm surge of Victoria Harbor had decreased at a rate of 2.6 & 4.8 mmyr-1 (1960~2008). The descending trend are much significant in Tai Po Kau tide gauge station. The trend on storm surge is generally consistent with the decline of tropical cyclones which entered the South China Sea and within the 800km range of Hong Kong. By observing the vibration of sea surface temperature anomolies as Pacific Decadal Oscilliation and El Nino Southern Oscillations, it is possibly related to the annual number of tropical cyclones and affect the chance of intense storm surge impact.

The projection on the storm surge intensity at the end of this century has been done in accordance with the result of Global Climate Models in IPCC AR4. The mean sea level is projected to rise for 0.18~0.59m but some of the researchers argue that the value is too conservative. The majority of global cimate models estimate that there is no significant change in the frequency of tropical cyclones but slightly increase in their overall intensity. In using the extreme projection of climate change, the return period of severe storm surge will be significantly shortened at the end of this century. The possibility of extreme sea level, causing serious damage to low lying area in the territority, tends to increase.