New threshold for landslide warning in the southern part of Thailand integrates cumulative rainfall with event rainfall depth-duration

A landslide-triggering rainfall threshold for the southern part of Thailand was introduced. The new threshold explicitly integrates the variables of event rainfall and cumulative rainfall from precipitation data corresponding to 92 landslide events in the study area. To determine event rainfall, a suitable inter-event criterion ( IEC ) had to be defined that separated two consecutive rainfalls. A rainfall intensity no greater than 2 mm/day lasting at least 1 day ( IEC 2,1 ) was the criterion established to separate two consecutive rainfalls in the study area. Using quantile regression, an event rainfall depth-duration ( ED ) threshold was drawn at a probability level of 5%. A 20-day cumulative event rainfall depth ( CR 20 ) was the most suitable duration of cumulative rainfall depth. A CR 20 of 100 mm was the third rainfall variable to give a threshold that integrated cumulative rainfall with event rainfall depth-duration ( CED ). This threshold is proposed for the study area depicted in three-dimensional space. The CED threshold is implemented by an assessment of CR 20 followed by an assessment of ED . The hit rate ( HR ) of the CED threshold is a little lower than the HR of the ED threshold, but the CED threshold is far better than the ED threshold in terms of false alarm rate ( FAR ) since the CR 20 of 100 mm filters out many non-triggering rainfalls prior to the assessment of the event rainfall.