Accelerating and Widespread Retreat of Global Estuarine Fronts

Estuarine-fronts retreat poses significant challenges as global environmental changes increasingly shape the frontal dynamics between estuaries and the sea. Prevailing interpretations frequently present inconsistencies, tending to prioritize terrestrial processes while underestimating the increasing impact of sea-level change. Here, we analyze high-resolution data on estuarine fronts positions from 1984 to 2024 across 18 of the world’s largest rivers with discharge higher than 5000 m ³ /s, revealing significant long-term retreat in all cases, with the Amazon exhibiting maximum retreat (102.9 km) and the Indus the least (8.4 km). We also find that most of the rivers posed accelerating retreating trends and six of which are among the top-9 large rivers (Amazon, Orinoco, Yangtze, Paraná, Irrawaddy and Mekong). Our analysis reveals that four major drivers—sea-level, river discharge, sediment flux and wind field—shape these patterns in different ways. Each of these factors singly dominates at least two rivers, accounting altogether for twelve rivers where retreat can be attributed primarily to one driver. In contrast, six rivers exhibit multi-factorial control, with two to three drivers acting jointly. These results demonstrate that estuarine retreat cannot be explained by a universal mechanism; instead, distinct rivers are governed by different combinations of terrestrial and oceanic processes. Oceanic influences, especially sea-level rise, are emerging as pervasive controls and normally with delayed responses. Given projections of sea-level rise of 0.63–1.01 meters by 2100, the accelerating retreat already observed is likely to intensify, with profound implications for biodiversity and ecological balance, highlighting the urgent need for adaptive management strategies.