The Effect of Variable Climate and Vegetation Cover on Catchment-Scale Erosion Rates

Abstract

The influence of variations in tectonics (rock uplift rates), climate, and associated vegetation cover (including other factors) on catchment processes has long been of interest to geomorphologists. However, the interactions of climate and vegetation with surface processes are relatively complex to understand. For example, an increase in precipitation supports vegetation growth and, at the same time, leads to high erosion rates. This study investigates the influence of different rock uplift rates and variations in precipitation and vegetation cover in catchment erosion at variable timescales (from millennial to daily timescales). The investigation is done through numerical simulations using a complex landscape evolution model (Landlab) modified to account for vegetation cover (and type) and remote sensing, and geographical information system (GIS). The model inputs were parameterized to four study areas with similar granodioritic lithology and distinct climate and ecological settings in Chilean Coastal Cordillera. Three sets of numerical simulations were conducted using Landlab: (1) To evaluate the role of changing rock uplift rates over the periodicity of variations in climate and vegetation at Milankovitch timescales (i.e., 21 kyr, 41 kyr, and 100 kyr) on long term catchment processes. (2) To identify which factor, precipitation or vegetation change is vital in influencing catchment erosion at season timescale. (3) The role of vegetation cover and type in influencing erosion rates during extreme precipitation events in present-day climatic conditions. The results indicate that at longer timescales, catchment processes are significantly influenced by Milankovitch timescale variations in climate and vegetation. These transient changes are superimposed upon tectonically driven rock uplift rates. At the seasonal timescale, precipitation variations pose a first-order control on catchment erosion, and the role of vegetation changes is secondary but still significant. However, at daily timescales, vegetation cover and type distribution play a more vital role (over precipitation variations) in controlling erosion rates during extreme precipitation events. Overall, this thesis augments the understanding of the significance of each natural driver (i.e., tectonics, climate, and vegetation) over others, at different timescales, on catchment-scale surface processes in distinct climate and ecological settings.