Environmental controls on landslide size distribution in the Paraitinga River basin, SE Brazil

The analytical treatment of some of the primary environmental controls on landslides has demonstrated that the landslide size distribution in the Paraitinga River basin, southeastern Brazil, are influenced by parameters such as triggering rainfall, lithology, slope gradient, upslope area, and land cover. Through the mapping of the surface of rupture of 1102 landslides triggered during an intense rainfall event in the summer of 2009/2010 and the fitting of a probability density function, we have discovered that the probability of large landslides occurring was significantly disturbed by lithology, slope gradients > 0.56 m/m, and triggering rainfall exceeding 180 mm within 48 h. In contrast, the probability density function for small landslides was affected by slope gradients less than < 0.31 m/m, rainfall less than 120 mm within 48 h, and higher values of upslope area. Moreover, the area of landslides in the probability peaks substantially increased when lithology consisted of schist or quartzite and in forested areas. These findings corroborate previous studies that establish a relationship between landslide size distributions and triggering processes, as well as the mechanics of landslides based on stability models, indicating a variation in triggering processes between the two segments of the curve: rollover (small landslides) and tail (large landslides).