Qualitative flood mapping as a tool for urban planning

Case study of Iguaçu watershed

Abstract

Urban flooding represents a growing challenge for contemporary cities, especially in densely populated areas. These events, typically caused by intense rainfall, are worsened by unplanned urbanization, which increases impervious surfaces, and by climate change, which intensifies the frequency and severity of precipitation events, as well as sea level rise in coastal regions. This study aims to map flood susceptibility in the Iguaçu River Basin, located in the Metropolitan Region of Rio de Janeiro, using the Physical Susceptibility to Floods Index (PhySFI)—a multi-criteria tool that assesses flood vulnerability based on four indicators: terrain slope, land use, proximity to water bodies, and elevation. The study also proposes a complementary analysis by cross-referencing the index results with historical flood records, validating the model in previously affected areas and identifying zones of residual risk. The results of this mapping showed good correspondence with the recorded events, lending robustness to the proposed methodology. Thus, the susceptibility map can be used as a basis for complementary analyses, offering a dual planning strategy that combines corrective measures in critical areas with the implementation of preventive actions in vulnerable zones, contributing to sustainable and resilient urban development.