Amplified response of Amazon floodplain flows to rising river levels

Abstract The dynamics of Amazon floodplains is tightly connected to the adjacent river flood pulse, yet its hydrological functioning differs from that of the main channel. While the river transports water downstream, floodplain flows promote lateral connection, facilitating biogeochemical exchanges with the river and sustaining local ecosystems and riverine communities. Extreme floods in the Amazon Basin have become more frequent in recent years, and their impact on floodplain flow remains unknown. Here, we show that floodplains flows of the lower Amazon basin can reach up to 40 000 m 3 s −1 during extreme floods, a magnitude comparable to the world´s largest rivers. While the mean (maximum) Amazon River flow has only increased by ∼4.7% (8.7%) since 2005, the mean (maximum) flow in the adjacent floodplain has increased by 60% (68%), corresponding to a relative increase approximately 13 times larger than that of the mainstem. This suggests a nonlinear and amplified hydrodynamic response, where small increases in river level produce disproportionately large relative increases in floodplain flow. Interestingly, the floodplain water extent shows only a moderate increase (13.5%), indicating that the recent intensification of Amazon River discharge does not primarily expand flooded areas but instead accelerates water movement within them. Such intensified flows may enhance fluvial erosion, sediment transport, and ecosystem disturbance, increasing the vulnerability of floodplain ecosystems and communities to extreme hydrological events and ongoing environmental changes. Our study indicates that actual changes in the Amazon floodplain flow are significantly larger than in the main river, calling for more studies to assess the impacts on the Amazon floodplain human populations and ecosystems.