Interaction between tectonics and climate encoded in the planform geometry of stream networks on the eastern Tibetan Plateau

Stream networks are highly abundant across Earth’s surface, reflecting the tectonic and climatic history under which they have developed. Prior studies suggest that stream branching angles are strongly correlated with climatic aridity, with a tendency toward wider branching angles in more humid climates. However, branching angles are also shaped by topography and thus by tectonic forcing. The importance of climate relative to tectonics, especially in tectonically active regions, remains ambiguous. Here we evaluate the relative dominance of climatic aridity and channel slope in shaping the branching angles of stream networks on the eastern Tibetan Plateau, a region with complex tectonics, variable climate, and diverse landscapes. Climatic aridity and channel slopes vary systematically from the relatively flat, dry interior to the steep, wet margin. Our analysis shows that the correlation between branching angles and climatic aridity reverses between the relatively flat interior and the steep eastern margin and the shift is observed in the transitional zone at intermediate topographic slopes. In the flat interior, branching angles are wider in wetter climates, consistent with previous studies in other regions. As one approaches the Tibetan Plateau’s eastern margin, however, branching angles become narrower as climate becomes wetter and topographic gradients simultaneously become steeper. These general patterns also persist after removing side-branches. These results indicate that climatic controls on branching angles are gradually overwhelmed by tectonic controls as one goes from the relatively flat terrain of the interior to the steeper terrain of the tectonically active eastern margin. Our findings demonstrate the joint influence of tectonic forcing and climate in shaping river network morphology.