2024 Brazil floods: Mapping the extent and impacts in Eastern Rio Grande do Sul using geospatial techniques

The May 2024 flood event in Porto Alegre, Brazil, marked one of the most severe hydrological disasters in the region's history. This study provides a high-resolution flood inundation assessment by integrating Sentinel-1 SAR, Sentinel-2 multispectral imagery, and Copernicus DEM-derived contours, overcoming the limitations of individual datasets. A key challenge in urban flood detection is SAR's insensitivity due to the double bounce effect and the limited spatial resolution of Sentinel-derived flood maps. To address this, we integrated high-resolution PlanetScope imagery for manual validation and used DEM-based contours to refine the flood extent in urban areas. Further, daily precipitation from the Global Precipitation Measurement Integrated Multi-satellitE Retrievals for the (GPM-IMERG) is considered for assessing the impact of precipitation on flooding. The analysis from precipitation revealed multi-day extreme rainfall from April 27 to May 4, with three consecutive days (April 30 – May 2) exceeding the 99.9 th percentile as the primary driver of the flooding. The flood extent map shows that 1481 ​km 2 of cropland and 76.2 ​km 2 of urban areas were inundated, significantly impacting critical infrastructures, including the Salgado Filho International Airport. These findings highlight the vulnerability of densely populated and agriculturally vital regions to extreme weather events exacerbated by climate change. The findings emphasize the urgent need for resilient infrastructure, adaptive urban planning, and robust mitigation strategies to manage the increasing risks of extreme weather events driven by climate change.