Detection of vulnerable areas to the occurrence of floods in tropical regions, from morphometric attributes

Floods are the principal natural disasters responsible for social, economic, and environmental damages in tropical and subtropical regions of Brazil. The objective of this research was to establish a procedure to remotely determine areas vulnerable to the occurrence of floods in a watershed using a geographic information system. Therefore, a morphometric analysis of the drainage network and the relief was performed in 170 hydrographic subbasins from the Alto Sapucaí watershed, Minas Gerais Southern and São Paulo Northeast states, Brazil. This study considered the following parameters: compactness coefficient, drainage density, stream frequency, roughness index, stream surface length and form factor or Gravelius´s shape index. Therefore, a cluster analysis was executed to identify similar characteristics in the 170 subbasins to discriminate those most susceptible to flooding due to the morphometric characteristics of the drainage, relief, and basins. It was possible to separate the subbasins into two groups. The first includes 85% of the area and did not present significant risks for floods. The second, which represents 15%, is classified as a risk zone. In the second group are the municipalities of Itajubá, Piranguinho, Santa Rita do Sapucaí, Piranguçu, and Delfim Moreira, which, according to the civil defense bulletins, suffer from recurrent floods. The diagnosis was followed by a list of suggestions for planning and managing areas subject to natural disasters. The procedure adopted was efficient and can be applied in other regions for the effective planning of public policies for the use and occupation of urban and rural areas, with lower financial costs and saving lives.