Report No. : GEO Report No. 364

Report Title : Territory-wide Rainfall-based Landslide Susceptibility Analysis (2022), 28 p.

Author : F.L.C. Lo, R.P.H. Law & F.W.Y. Ko

Abstract

The previous landslide susceptibility map for natural terrain in Hong Kong has its limitations for direct application, such as in predicting number of natural terrain landslides in a rainstorm and undertaking global analysis, for example, global quantitative risk assessment and priority ranking. To overcome the limitations, a new territory-wide rainfall-based landslide susceptibility analysis was developed that correlates rainfall and landslide density with slope angle and solid 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 solid geology were considered. For each terrain unit, a year-based correlation between normalized maximum rolling 24-hour rainfall and landslide density was obtained. Global adjustment factors were recommended to transform the year-based correlation to the storm-based correlation. Storm-based correlation based on normalized maximum rolling 4-hour and 24-hour rainfalls was also developed using the same methodology.

For the time being, the new susceptibility model would be applied in predicting number of natural terrain landslides in a rainstorm and undertaking global analysis, for example, global quantitative risk assessment and priority ranking. However, the resolution and reliability of the model are not yet sufficient to support direct application for site-specific hazard assessments and risk-based decision making at this stage.

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