Divergent drainage-scale responses to lithological heterogeneity.

Despite widespread recognition that lithological heterogeneity helps shape river networks, a widely applicable topographic diagnostic for whether and where lithological contrasts drive drainage reorganization is still lacking. Here, we introduce a drainage-network metric, the rock proportion-contributing area order (RP-CAO) relationship, and further show that responses diverge with drainage scale: small, low-discharge channels divert around resistant rocks, whereas large, high-discharge rivers largely maintain their course and incise through them. We capture this divergence by tracking rock-type enrichment along the network as a function of contributing area. Across landscape evolution simulations and natural river networks, the enrichment-scale relation forms a robust V-shaped pattern that quantifies these end members. Applied to networks along the eastern Tibetan Plateau, it isolates where lithology most strongly localizes rerouting and divide mobility despite strong spatial variability in tectonic and climatic influences. Requiring only topography and lithological maps, the framework enables comparable tests of drainage reorganization driven by spatially discrete lithological contrasts across mountain belts worldwide.