Susceptibility Map of Landslides Triggered by Rain in the Metropolitan Area of San Salvador (AMSS)

The Metropolitan Area of San Salvador (AMSS) is under the spectrum of different threats of natural origin. From the volcanic risk posed by the San Salvador volcano, up to the seismic, flooding and landslides hazards, this paper focuses on the latter. This threat is not only caused by natural phenomena, but also by human factors which have a decisive influence on it due to the pressure that urban sprawl represents on the territory. In this process of rapid urbanization of cities, the most vulnerable sectors of the population have tended to settle in areas with a higher degree of risk (banks of rivers and streams, mountain slopes, volcanoes surroundings, and others). For the foregoing, it is important for planning offices, to have the right tools, standards and skills that can be of help in their decision-making processes regarding urban planning of their territory .

Given this background, characterizing on maps the threat of landslides, is based on the analysis of susceptibility obtained from landslide inventory maps which show movements naturally triggered. This is done by using the bivariate method and considering conditioning factors of the land (geology, slope, aspect, geomorphology, fracturing and land uses). The introduction of anthropic factor in this analysis has been dealt with on the basis of drawing up a map of density, considering those landslides caused by human actions (anthropic density). Crossing this latter map with natural susceptibility, gives us a more realistic idea about the threat studied. Finally, rain as triggering factor is added using a modification of the Mora-Vahrson method which considers maximum daily precipitation for a given return period. The resulting map allows us to identify areas of a metropolitan area where the susceptibility to landslides ranges from low, moderate, to high and very high.