Coping with landslide risks in Hong Kong under extreme storms: Storm scenarios, cascading landslide hazards and multi-hazard risk assessment

(RGC CRF, 2016-2019, PM: Zhang, L.M.; Co-I: Dr Cheung, Wai-Man, Raymond; Prof Jiao, Jimmy Jiu-Jiu, Dr Lee, Tsz-Cheung; Prof Ng, Charles W. W.; Prof Tung, Yeou-Koung; Dr Zhao, Jidong)

Slope failures in Hong Kong are frequently triggered by rainstorms. For example, a severe rainstorm hitting Lantau Island in June 2008 caused about 1,600 natural terrain landslides, 900 debris flows and 600 flood spots. If the same rainstorm were to hit Hong Kong Island, the current slope safety system would be stretched to its limit. The capacity of the system would be exceedingly overwhelmed upon more extreme rainfall. According to the studies of the Hong Kong Observatory, the annual rainfall in Hong Kong is expected to be more variable and the frequency and intensity of extreme rainfall events may increase over time under the influence of the changing climate. Under extreme rainfall conditions, multiple hazardous processes such as landslides, debris flows and flooding may occur simultaneously or sequentially, resulting in cascading hazards increasing the risk. In the worst cases, interactions among these hazards can generate new hazards of greater destructive power such as formation of landslide dams and dam breaching. It is important to identify the catastrophic hazard scenarios that could be generated in Hong Kong and the corresponding bottlenecks in the slope safety system, and to make recommendations for improving preparedness and system safety.

The primary objective of this project is to develop a stress-testing framework for assessing the landslide risk in Hong Kong under extreme rainstorms caused by the changing climate. This project will, for the first time, address the issue of slope safety under extreme rainstorms within a novel framework of ‘stress testing’ by integrating the strengths of two universities (HKUST and HKU) and two government departments (Geotechnical Engineering Office and Hong Kong Observatory). Stress testing is defined as a targeted reassessment of safety margins of a given system in light of extreme events. It involves testing beyond normal operational capacity, often to a breaking point. The scientific tasks of this project include (1) identification of plausible future critical storm scenarios considering climate changes, (2) evaluation of slope system response under extreme rainstorms using advanced multi-scale hydrological and geotechnical processes modelling algorithms and advanced centrifuge modelling techniques, (3) multi-hazard risk assessment, and (4) formulation of a unique stress-testing framework for evaluating the Hong Kong slope safety system. The bottlenecks of the present Hong Kong slope safety system will be identified and the areas of improvement to the system will be recommended to the policy makers.

The proposed multi-scale multi-process modelling techniques will advance the state-of-the-art in hazard analysis. The stress-testing framework for landslide risk management can be applied to other regions of similar climate conditions and to other engineering systems.