Supplementary file 1_Unprecedented suspended solids load caused by record-breaking extremes in southern Brazil: the May 2024 event.docx

In May 2024, intense precipitation and flooding impacted southern Brazil in what became the country’s worst climate disaster. The unforeseen volume of runoff was funneled into Patos Lagoon, the world’s largest choked coastal lagoon, transporting large amounts of suspended solids (SS) from the watershed and eroded margins. In this study, we estimate SS concentration, discharge, and mass budget in Patos Lagoon during the May 2024 extreme flood event. Given the challenges of monitoring such extreme events, a multi-proxy approach was adopted, integrating optical satellite data with in situ gravimetric samples, gauging station records, rating curves, and ADCP measurements. Results revealed unprecedented water discharge rates (May 2024 monthly average of 1.78×104 m³/s, 37% above the historical maximum) and high SS concentrations (up to 463 g/m³). Between April 1st and June 30th, more than 9 million tonnes of SS were delivered to the Patos Lagoon (9.77×106 ± 6.75×106 t), exceeding the typical annual load and comparable to about one month’s worth of the SS discharge from the Río de La Plata. This study provides the first estimate of the SS mass budget for Patos Lagoon, suggesting that most of the SS was exported to the coastal ocean, while a fraction likely accumulated within the lagoon. These findings offer a foundational understanding of how extreme hydrometeorological events influence sediment dynamics in choked coastal systems.