Geomorphic constraints on landscape sensitivity to climate in tectonically active areas

The geomorphology of fluvial landscapes is known to record information about uplift rate, spatial patterns of faulting, and tectonic history. Data is far less available when addressing the sensitivity of common geomorphological metrics, such as channel steepness, to climatic boundary conditions. We test the relationship between channel steepness and precipitation rate by measuring a large number of channels in different mountainous areas. These regions exhibit a tenfold variation in precipitation rate between them (~ 100-1000 mm y− 1) but have similar uplift rates, allowing the tectonic variable to be controlled. By accounting for the orographic coupling of rainfall with uplifted topography, we find that channel steepness is significantly suppressed by higher precipitation rates in a measurable way that conforms to simple stream power erosion laws and empirical constraints on their parameters. We demonstrate this using modern and estimated glacial precipitation rates; and climate emerges as an important, quantifiable control on channel geometry. These findings help to explain why highly variable measurements of channel steepness are reported from different locations and provide important empirical constraints on how climate shapes tectonically active landscapes.