Rainfall Threshold for Landslide Warning in Southern Thailand – An Integrated Landslide Susceptibility Map with Rainfall Event – Duration Threshold

Southern Thailand is one of hotspots for landslides. So far, the rainfall triggered landslides in this region caused many sufferers and fatalities. On the basis of the rainfall data that triggered ninety-two landslide events during 1988–2018 and the landslide susceptibility maps published by the Department of Mineral Resources (DMR), this study introduced rainfall event-duration (ED) thresholds, namely EDm and EDh thresholds, for the places classified as the modest and the huge susceptibility levels, respectively. The modest susceptibility is a combination of very low, low, and moderate landslide susceptibility levels indicated in DMR maps. The huge susceptibility is a combination of high and very high landslide susceptibility levels indicated in DMR maps. Indicated by an area under the receiver operating characteristic curve (AUC), the EDm and EDh thresholds yielded the significantly better predictability than the original threshold did. Furthermore, the EDm threshold yielded the perfect prediction with AUC of 1.00.