Predicting landslides from rainfall in a humid, sub-tropical region

Abstract Topography, geology and a humid, sub-tropical climate make the Durban region on the east coast of South Africa particularly prone to sliding mass movements. Records of individual landslides and landslide events between 1970 and 1990 were compared with 22 rainfall variables calculated for the same period. Correlation coefficients demonstrated statistically significant relationships between annual and wet season landslide frequencies and maximum 3-day and maximum monthly wet season rainfall, whereas precipitation for shorter and longer periods was unrelated. Envelopes of critical values for cycle and total coefficients based on the percent of mean annual rainfall were identified for both the timing and magnitude of landslide events. They suggest a two-stage equilibrium condition for the rainfall-mass movement relationship, controlled by average wet season rainfall. Moreover, once the pattern of rainfall for any particular wet season is established, the envelopes allow the prediction of rainfall conditions necessary for landslides to occur. The likelihood of an inaccurate prediction is approximately 10%.