Earth Observation Records of Extreme Sediment Mobilization in the World’s Largest Choked Lagoon During the 2024 Southern Brazil Flood Catastrophe

The 2024 catastrophic floods that devastated the southern Brazilian state of Rio Grande do Sul also affected the coastal environment of the world’s largest choked lagoon, the Patos Lagoon (PL). Given its size, satellite imagery presents an incomparable advantage to evaluate the effects of the floodwaters entering this ecosystem. To obtain a general overview of the event in the lagoonal water body, this research utilized Sentinel-3 OLCI data to remotely estimate suspended particulate matter (SPM) concentrations in every available image between January and August 2024. Our results show that the fluvial pulse generated from the extreme rainfall produced a sediment plume that, at its maximum, covered an area of over 3,000 km², representing ~ 29% the water body. This plume may have carried up to an unprecedented 5 million tons of SPM into the lagoonal system. This vast amount of SPM is likely to get trapped in the lagoon, disrupting multiple aquatic ecosystem services such as fishing or navigation. The multiwavelength SPM approach we employed performed satisfactorily to describe the water dynamics in the study before, during, and after the extreme event. Moreover, our findings indicate that during the study period, the turbidity in the lagoon was primarily controlled by SPM. Future climate change scenarios forecast an increase in rainfall in the hydrographic basins that discharge to the PL. This threat makes evident the necessity of permanent water-quality monitoring for adaptation and mitigation strategies in this water body.