Climatic and Tectonic Forcing Lead to Contrasting Headwater Slope Evolutions

Abstract. Landscapes evolve through the coupled effects of tectonics and surface processes. Previous studies have shown that uplift rate changes generate upstream-migrating erosion waves, altering downstream slopes while upstream ones remain constant until the wave arrives. However, the distinctive differences between landscape responses to uplift versus climatic changes, particularly rainfall rate changes, remain incompletely described. This study uses a numerical model to investigate landscape responses to changes in both rainfall and uplift rates. Results show that, unlike the simple upstream-migrating erosion waves from uplift rate changes, rainfall rate changes generate more complex responses. Specifically, rainfall rate changes cause transient slope change reversals at the headwaters due to differential erosion between the divide and its adjacent areas, a pattern not observed in uplift-induced evolution. These reversals are more pronounced when hillslope diffusion plays a dominant role (i.e., high diffusion coefficient). While both tectonic and climatic forcing drive landscape change, they produce recognizably different signatures in river profiles. If these distinctive signatures can be identified from river profiles or inferred from erosion rate measurements, they can help disentangle climatic and tectonic influences on landscape evolution.