Risk Matrix of Hydrological Disasters Combining Rainfall Thresholds and Social-Environmental Criteria

This paper presents a procedure for risk assessment for hydrological disasters considering the threshold rainfall and environmental and social criteria. A case study was carried out to test its feasibility in the northern region of the State of São Paulo, Brazil. The advantage of this procedure is that it only uses data available on government institutions and websites. For this reason, other regions and countries can easily adapt the procedure to their reality. Initially, the hydrological disasters were obtained including date, type of disaster, geographical coordinates and the number of victims. Next, for each disaster, the daily rains corresponding to the dates of the events were obtained from government websites, to establish the rainfall thresholds. Social criteria weighted the poverty index, population density, and the elderly population. The Environmental criteria weighted hydrology, geomorphology and geology factors. An open-source Geographic Information System (GIS) enabled the spatial distribution of disasters through the characterization of the physical environment in hydrology, geomorphology and geology features. The risk assessment was then obtained by combining the rainfall-triggering event with the environmental Susceptibility with social vulnerability. As a result, 31 of the 138 studied municipalities suffered from hydrological disasters, accounting for 99 occurrences between 2002 and 2017.