Cameron Highland is classified as one of the landslide-prone areas in Malaysia due to its hilly landform. It has been discovered that the landslides in Cameron Highland were mainly triggered by the intense rainfall since the area encountered high amount of rainfall throughout the year. This study is carried out to evaluate the correlation between the rainfall intensity- duration (I-D) and the landslide occurrences in the Cameron Highland area. Twelve cases of landslides in the study area had been selected for conducting the analysis of rainfall intensity- duration (I-D) that triggers the landslides. The important variables from the analysis such as the maximum rainfall intensity (I) and the duration of rainfall series (D) have been applied to establish the empirical rainfall intensity-duration (I-D) threshold for Cameron Highland landslide areas. Based on the study, by utilising the logarithmic scale graph and applying a power-law model from the general equation of 1= <xDp, the empirical I-D threshold for Cameron Highland landslide was determined as I = 29.088D0075 (I = rainfall intensity in mm/hr and D = duration in hour). The empirical (I-D) threshold can be a functional mechanism for the Early Warning System (EWS) once it is further developed, that enable the relevant authority to prepare mitigation measures such as evacuation, spreading information to the civilian in order to prevent major losses and casualties due to the landslide events.

Empirical rainfall thresholds for the purpose of shallow landslide forecasting are proposed for Peninsular Malaysia where numerous slope failures are reported due to the intense rainfall in conjunction with the humid tropical climate. Thirty-seven cases of landslide-triggering-rainfall were selected from 1993 to 2018 to identify the correlation between rainfall and shallow landslide through the analysis of specific rainfall events. The derived rainfall parameters were applied to establish two rainfall thresholds of (Imean-D) and (Imax-D) via practical methods. For the identical range of event duration 1 < D < 263 h, the (Imean-D) threshold formula was expressed as I = 17.5 D−0.722, while the (Imax-D) threshold was defined as I = 37.8 D−0.114. Both thresholds performed different functionalities with a primary goal of predicting shallow landslides. When both (Imean-D) and (Imax-D) thresholds were compared with the thresholds proposed by various studies worldwide, both dominated the upper positions. More rainfall is required for land sliding due to the high thickness of the Malaysian soil that is associated with the abundant tropical downpour. From the perspective of the antecedent, the period of prolonged precipitation or short heavy rainfall from 1 to 10 days can result in shallow landslides for Peninsular Malaysia. In the context of geology, the igneous rock type of granite has the highest susceptibility to the shallow landslide at 65%, despite other rock types of sedimentary and metamorphic. The threshold validation depicted all True Positive events for the (Imax-D) threshold, and one Negative False event for the (Imean-D) threshold. The (Imean-D) threshold was revised to acquire the new value, but it needed to deal with the possibility of False Alarm and the (Imax-D) threshold seemed to be more credible to represent the rainfall-induced shallow landslide threshold for Peninsular Malaysia.

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