Observed streamflow data shows El Niño–Southern Oscillation increases likelihood of extreme events in South America

Understanding how the El Niño–Southern Oscillation influences extreme streamflow events is essential for anticipating water-related risks in South America. Here, we analyse the relationship between this climate phenomenon and the likelihood of floods and droughts using a multi-decadal observational dataset of river discharge. We quantify how the probabilities of extreme events shift under different phases of the El Niño–Southern Oscillation. The results show that flood likelihood increases by over 120% during El Niño in the La Plata Basin and by over 120% during La Niña in the northern Amazon. Maximum precipitation and streamflow signals are generally aligned, but flood flows exhibit stronger amplification than high precipitation, suggesting a cumulative climate effect on extreme events. In contrast, increased drought probabilities of more than 120% is linked to El Niño in the Amazon, while La Niña raises drought risk in inland South America of more than 80%.