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ABSTRACT Heavy rain events or rainstorms of various scales often occur in Hong Kong from April to September. In extremes cases, they lead to serious landslides and flash floods resulting in loss of life, and damage to property and infrastructure. With climate change, extreme rain events are projected to be more frequent and more intense in this region. A system to gauge and label the severity of rainstorms would be useful for identifying and communicating extreme conditions in warning and disaster prevention operations. In parallel, a better understanding of the characteristics of rainstorms would also be important for impact assessments and engineering design purposes. This paper formulates a practical framework to index the magnitude and severity of rainstorms in Hong Kong. An index termed as the Severity Index combining the magnitude of different rainstorm attributes is devised for quantifying the overall severity of rainstorms. This index is flexible to allow tuning for specific applications. [ABSTRACT FROM AUTHOR]

In Hong Kong, rain-induced shallow slope failures are recognized as one of the most catastrophic hazards due to Hong Kong's hilly terrain and frequent heavy storms. Due to climate changes, extreme storms are expected to be more frequent and intense in the future. The prediction of shallow slope failures under extreme storms is therefore essential. This study aims at simulating likely shallow slope failures on western Hong Kong Island under extreme storms. The terrain and slopes are discretized into a grid of cells on a geographical information system. Then, the pore-water pressure regime in the ground is analyzed through an infiltration analysis. Next, the slope stability and debris movement are assessed using a well-established model, which has been validated with landslides triggered in two past storm events. Finally, the shallow slope failures under three extreme storms at 44, 65, and 85% of the probable maximum precipitation are simulated. Under such extreme storms, more than 300 major slope failures may occur, occupying 0.5-1.7% of the natural terrain area. Some of the simulated movement traces and deposition locations are close to the urban area, calling for new strategies for landslide risk management. [ABSTRACT FROM AUTHOR]