Abstract
This study demonstrated the relationship between rainfall intensities-durations (I-D) associated with shallow landslides and defined the empirical rainfall I-D threshold for the initiation of shallow landslides in Japan. New thresholds were also compared with global, regional and local scale rainfall I-D thresholds proposed by previous studies.
The rainfall I-D threshold was defined by the equations I = 2.18*D^(-0.26) (where I and D are average rainfall intensity in mm/h and rainfall duration in hours from beginning of rainfall to landslide occurrence, respectively). The rainfall I(MAP)-D (normalized) threshold was expressed as I(MAP) = 0.0007*D^(-0.21) (where I(MAP) is normalized average rainfall intensity from beginning of rainfall to landslide occurrence with respect to the MAP(mean annual precipitation) in h^(-1)).
In comparison with other rainfall threshold proposed by previous studies, new rainfall I-D and I(MAP)-D (normalized) thresholds were lower than those for the world, in humid subtropical region, in the Asia monsoon region and in Japan. We can therefore conclude that rainfall I-D conditions and new thresholds revealed the regional potential of landslide hazard in Japan which was characterized by heavy rainfalls with long-term duration during the East Asia summer monsoon season.
