Roles of different controls influencing the intensity–duration rainfall thresholds for triggering landslides: an intercomparison of published thresholds

Abstract Rainfall thresholds for triggering landslides are crucial to forecasting landslide occurrences. Various site-specific conditions, determination methodologies, and targeted scales (extent of the area in which the rainfall threshold is defined) can influence the rainfall thresholds. The predicting power of rainfall thresholds can be upgraded by clarifying and quantifying the effects of the controlling factors on them. Studies on rainfall thresholds have dramatically increased recently, creating an opportunity to compare them and enhance knowledge about the effects of those controlling factors. Therefore, this study focused on collecting and intercomparing published rainfall thresholds to determine the effects of different controlling factors. We focused on the empirical intensity–duration and total event rainfall–duration type thresholds because they are the most common to date. We compiled information about published rainfall thresholds from various countries and regions and analyzed the variation of rainfall threshold parameters and critical rainfall intensities according to the different controlling factors. Our study shows that the quality and quantity of data, particularly the number ( N ) and the rainfall–duration range width ( DRW ) of landslide-triggering rainfall events used to define rainfall thresholds and targeted scales, might be crucial in determining rainfall thresholds for occurring landslides rather than site-specific conditions, such as geology and climate. Our findings indicate that thresholds for triggering shallow landslides and debris flows determined with N > 100 and DRW > 30 h often exhibit considerably narrower variation ranges and higher reliability than those with fewer events and shorter duration ranges, although there were large differences in site-specific conditions.