The establishment of rainfall thresholds for debris slide in Taiwan-With the combination of multivariate analysis and the I-R index

Abstract

Catastrophic landslides and debris slides triggered by intense typhoons such as Typhoon Morakot (2009) occurred more frequently in the recent years, and caused many casualties and economic loss in Taiwan. For the purpose of reducing the damage resulted from geological hazards, this study collects landslide inventories which contain the information of occurrence time, location, magnitude, rainfall intensity, accumulated rainfall and tries to establish the rainfall threshold for debris slide. This study adopts the concept of risk matrix, combining the magnitude (landslide ratio of slope units) and the possibility of occurrence (historical disaster records) to set up the warning thresholds. Critical rainfall thresholds are build up according to the R24 (24 hours accumulated rainfall, as long-term rainfall) and I3 (3 hourly mean rainfall intensity, as short-term rainfall) of historical disasters. Validation with recent typhoon event shows the threshold can forecast the landslides in 2~9 hours in advance which may be enough for the evacuation. An early-warning system is also built and the results can be applied to regional land-use planning and disaster prevention.