The relationship between the probability of landslide occurrence and rainfall

A study of rainfall and the number of landslides is presented using 5 min rainfall records for all rainfall gauges in Hong Kong Island over a 10 year period. The results indicate that rainfall of 1-12 h duration is important in predicting the number of landslides, and that antecedent rainfall also has some influence. Analysis of the data gives general threshold rainfall values causing isolated landslides. Models predicting the number of landslides from rainfall near a specific rain gauge are developed. Rainfall for a 1 in 100 year event is calculated and utilized in the prediction of the number of landslides caused by such a storm event over the area of Hong Kong Island. Thus, the number of landslides for a substantial area, versus annual exceedance probability, can be approximately predicted using only rainfall data and records of landsliding. This approach can be utilized wherever landslide and detailed rainfall and landsliding records are, or can be, kept.