Vegetation-precipitation controls on Central Andean topography

Abstract

Climatic controls on fluvial landscapes are commonly characterized in terms of mean annual precipitation. However, physical erosion processes are driven by extreme events and are therefore more directly related to the intensity, duration, and frequency of individual rainfall events. Climate also influences erosional processes indirectly by controlling vegetation. In this study, we explore how interdependent climate and vegetation properties affect landscape morphology at the scale of the Andean orogen. The mean intensity, duration, and frequency of precipitation events are derived from the TRMM 3B42v7 product. Relationships between mean hillslope gradients and precipitation event metrics, mean annual precipitation, vegetation, and bedrock lithology in the central Andes are examined by correlation analyses and multiple linear regression. Our results indicate that mean hillslope gradient correlates most strongly with percent vegetation cover (r = 0.56). Where vegetation cover is less than 95%, mean hillslope gradients increase with mean annual precipitation (r = 0.60) and vegetation cover (r = 0.69). Where vegetation cover is dense (>95%), mean hillslope gradients increase with increasing elevation (r = 0.74), decreasing inter-storm duration (r = −0.69), and decreasing precipitation intensity by ~0.5°/(mm d−1) (r = −0.56). Thus, we conclude that at the orogen scale, climate influences on topography are mediated by vegetation, which itself is dependent on mean annual precipitation (r = 0.77). Observations from the central Andes are consistent with landscape evolution models in which hillslope gradients are a balance between rock uplift, climatic erosional efficiency and erosional resistance of the landscape determined by bedrock lithology and vegetation.