Dynamics of Yearly Maximum Water Levels in the Amazon Estuary

Abstract The magnitude and temporality of the yearly maxima water levels are key parameters for the characterization of the riverine flooding hazard and its impacts. Although the Amazon estuary, that conveys the largest river discharge to the world ocean, exhibits marked events of maxima of the water level every year, the contribution of the natural drivers to these yearly extreme water levels is not well quantified. In this study, we investigate the contributing factors to the yearly maxima water level events along the Amazon estuary using a high-resolution cross-scale hydrodynamic model that has been extensively validated against comprehensive in situ and satellite datasets. Our study shows that the oceanic tide plays a crucial role in the genesis of the yearly maxima, whose influence decays from the downstream part (accounting for 85% of the total water level) towards the upstream part (44% of the total water level) of the estuary. Conversely, the Amazon discharge during the peak flood season induces yearly maxima in the upstream part of the estuary (accounting for 41% of the total water level), but the riverine influence decays sharply towards downstream and remains minor in the region of the mouths (9% of the total water level). Additionally, the sporadic bursts of north-easterly trade winds result in a sizeable wind-setup in the estuary (typically accounting for 5% to 13% of the total water level). Our study underscores the need for considering compound forcing in the cross-scale modeling in Amazon and similar estuaries. At a time when the climatic extremes are becoming more frequent over the Amazon region, our study helps the interpretation of the imprint of these extremes on the water level variability along this estuary.