In April-May 2024, unprecedented floods in Rio Grande do Sul displaced around 600,000 people and caused more than 180 deaths. This study unpacks the role of anthropogenic climate change and the preceding El Niño conditions on the extreme rainfall using a probabilistic event attribution. This event was rare even in the 2024 climate, with a return period exceeding 100 years. With global warming of 1.2°C, such an event has become approximately 2 (0.06 to 4200) times as likely, or equivalently 12% (-13 to +43%) more intense. The recent El Niño event also approximately doubled (0.7 to 37 times) the likelihood of such an event relative to a neutral year. In any disaster, the vulnerability and exposure context play a crucial role in turning the meteorological hazard into impacts, underscoring the need for equitable adaptation measures to break the cycle of risk and inequality in the context of a warming climate.