Triggering factors and critical thresholds for landslides in Rio de Janeiro-RJ, Brazil

Abstract

The city of Rio de Janeiro undergoes periods of intense rainfall, and due to its geological and topographic characteristics, it is highly susceptible to landslides. Numerous structures have been built in areas at risk for landslides, using substandard techniques, primarily in poor neighborhoods. Critical thresholds for landslides in the city of Rio de Janeiro were established based on the combined effect of hourly intensity and accumulated rainfall over 96 h and an inventory of landslide available at Geotechnical Institute Foundation of Rio de Janeiro (GEO-RIO). Landslide events that occurred in the city from 1998 to 2002 were compared to those that took place from 2010 to 2012. The study aims to verify the effects of the slope stabilization work carried out by GEO-RIO and the population growth in areas highly susceptible to landslides during this period. The results indicate that the triggering factors for landslides in most of the areas were unchanged during these periods. Nevertheless, in spite of the investments in slope stabilization, the analyses pointed to a worsening condition in the most recent period for some regions, probably due to the increase in the irregular occupation (slums) in those areas. Some regions of the city were shown to be more susceptible to sliding than others due to differences in rainfall, geology, geomorphology and type of occupation. The results indicate that the early alarm system for the Rio de Janeiro city should be improved by specifying zone-dependent thresholds.