Rainfall-based landslide susceptibility analysis for natural terrain in Hong Kong - A direct stock-taking approach

The steep natural terrain in Hong Kong, combined with deep weathering profile and high seasonal rainfall, is highly susceptible to rain-induced, shallow landslides. With over 35 years of practice in landslide risk management, Hong Kong has progressively built up a series of important databases that facilitate conducting novel technical development work related to natural terrain landslides. Amongst others, there is a dense network of raingauges that provides state-of-the-art rainfall records, a high-resolution inventory of historical landslides and a LIDAR-based digital terrain model for the natural terrain. This paper discusses the previous landslide susceptibility map for natural terrain in Hong Kong and its limitations, and then presents a new territory-wide rainfall-based landslide susceptibility analysis that takes cognizance of the effects of slope angle and bedrock geology. The year-based susceptibility model correlates landslide density with normalized maximum rolling 24-hour rainfall. Twenty-four terrain units, comprising eight classes of slope angle and three classes of bedrock geology are considered. For each terrain unit, a year-based correlation between normalized maximum rolling 24-hour rainfall and landslide density is obtained. Global adjustment factors are recommended to transform the year-based correlation to the storm-based correlation. The potential applications of the outcomes of the landslide susceptibility analysis are also discussed.