Global alluvial channel patterns.

Quantitative analysis of alluvial channel patterns is essential in fluvial science, as their morphology both reflects and influences river behavior through interactions with water and sediment regimes, landscape processes, and human interventions. However, a comprehensive global study to identify predominant channel patterns and their underlying mechanisms remains lacking. Here, we map global alluvial channel patterns using high-resolution satellite observations. Our results reveal a hidden dominance of anabranching channels that surprisingly constitute half (51%) of total reach length globally, exceeding meandering (24%), straight (18%), and braided (7%) channels. In non-mountainous settings, anabranching channels dominate most continents except Oceania. They are not confined to typical alluvial lowland systems, also comprising 50% of alluvial tracts in mountains. While anabranching is typically associated with gentle slopes and expansive floodplains, these conditions are not exclusive determinants. The prevalence of anabranching channels transforms fundamental perspectives on global river systems, posing challenges for the fluvial geomorphology community.