Analysis of critical value of rainfall to induce landslides and debris-flow in Mt. Bawakaraeng Caldera, South Sulawesi, Indonesia

Mt. Bawakaraeng Caldera has been affected by tens of destructive landslide and debris-flow in recent years, triggered by rainfall episodes, which were responsible for many deaths and very important economic losses. Among the instability causes, meteorological factors are of primary importance in the Jeneberang Watershed, South Sulawesi namely the high recurrence rate of rainfall triggering landslides and debris-flow. The cumulative rainfall method is used to reconstruct both absolute and calibrated antecedent rainfalls associated with each major landslide and debris-flow event. The critical rainfall combination (amountduration) responsible for each landslide and debris-flow event was assessed and rainfall threshold for landslide and debris-flow was calculated. Rainfall-triggered landslides and debris-flow in the study area are ruled by the function I=86.517I)^-0.408, where I is the rainfall intensity in mm/day and D is the duration of rainfall in days. They are related both to short duration precipitation events (1-3 days) with high average intensity (between 82 and 90 mm/day) and long-lasting rainfall episodes (1-5 months) with a lower intensity (between 10 and 15 mm/day).