Climate-Driven Landscape Evolution Encoded in Stream Network Geometry

Abstract:

Climate signatures recorded in the geometry of branching streams provide insight into climate and landscape histories on Earth and other planetary bodies. Recent findings establish that branching angles vary systematically with climate, widening to ∼72° with increasing humidity. Here we demonstrate that in US watersheds, the relative slopes of confluent streams control their branching angles: streams with a greater difference in slope tend to branch at wider angles. Distributions of slope ratio are climate dependent, as branching streams in more humid landscapes are less likely to share a common slope than those in arid landscapes. This observation may be explained by the inhibition of runoff erosion and increasing role of soil creep in humid climates, which create and maintain ridges and valleys that disrupt the regional gradient. Our findings imply a ubiquitous topographic control on erosion, challenging the prevailing interpretation that groundwater seepage accounts for branching angles widening with humidity.