Flood-prone areas based on physiographic indices and multi-criteria assessment for the basins of Ubatuba, on the mountainous North Coast of São Paulo State, Brazil

The municipality of Ubatuba, São Paulo State, Southeast Brazil, is known for its strong orographic rainfall as a result of moisture fronts in the Atlantic Ocean, morphological structure, and abrupt relief of Serra do Mar. These conditioning combinations reinforce the occurrence of natural disasters such as runoff, floods, and landslides. There are several indices to assess flood hazard with different individual characteristics, but not an integrated index, based on traditional approaches. We used the compactness coefficient, circularity ratio, sinuosity index, drainage density, and curve number to propose an integrated index based in a multi-criteria assessment. Hence, the aim of this study was to propose and discuss an integrated index for morphometric and land use and land cover analysis of the Ubatuba municipality watersheds based on a decision matrix. Overall, the integrated multi-criteria index was efficient in discriminating hazard areas to flooding on the north coast of São Paulo, with 82.35% of the watersheds studied being identified with moderate hazard. The use of an integrated multi-criteria index using relief, LULC and soil type, an empirical parameter used in the determination of direct surface runoff from excess rainfall, and hydrography features helps in the interpretation of local hazard to flooding and contributes to urban planning, flood warning systems, and water resources management.