Influence of the number of vulnerability classes in determining morphometric susceptibility to flooding

Abstract Watershed morphometry is an important tool to diagnose susceptibility to flooding. This diagnosis can guide the planning and implementation of mitigation measures to avoid flooding damage. The objective of this work was to study flooding susceptibility in Espírito Santo Stream Basin (ESSB), located in the municipality of Juiz de Fora, Minas Gerais, Brazil, based on its morphometric characterization using two, three and five classes of vulnerability. In order to accomplish this, the basin was divided considering two levels of detail: in the first, less-detailed level, three sub-basins were generated; and in the second, more-detailed level, 65 watersheds were generated. Morphometric susceptibility to flooding was evaluated in these study units and the results were compared using the K-means and Fuzzy C-means clustering techniques. The results showed that the number of classes adopted affects the result of classification vulnerability, suggesting that cluster validation criteria can be used to delimit the choice of the number of classes to be adopted. Groups formed only by morphometric similarities differ from those obtained by the methodology based on classification of areas susceptible to flooding, since the methodology for susceptibility analysis transforms the numerical values of each morphometric parameter in a class of susceptibility.