Effect of changing vegetation on denudation (part 2): Landscape response to transient climate and vegetation cover

We present a numerical modelling investigation into the interactions between transient climate and vegetation cover with hillslope and fluvial processes. Model simulations were designed to investigate the effects of climate change and associated changes in surface vegetation cover on topographic basin metrics such as: slope, relief and channel steepness. The Landlab surface process model was used to evaluate the effects of temporal variations in vegetation cover on hillslope diffusion and detachment limited fluvial erosion. A suite of simulations were conducted to represent present-day climatic conditions and satellite-derived vegetation cover at the four EarthShape study areas as well hypothetical transient long term changes. Two different transient variations in climate and vegetation cover include a step change in climate or vegetation, as well as 100 kyr oscillations over 5 Myr. Results indicate that the coupled influence of surface vegetation cover and mean annual precipitation shifts basin landforms towards a new steady state, with the magnitude of change highly sensitive to the initial vegetation and climate conditions of the basin. Dry, non-vegetated basins show higher magnitudes of adjustment than basins that are situated in wetter conditions with higher vegetation cover. For coupled conditions when surface vegetation cover and mean annual precipitation change simultaneously, the landscape response tends to be weaker. When vegetation cover and mean annual precipitation change independently from each other, higher magnitude shifts in topographic metrics are simulated. Changes in vegetation cover show a higher impact on topography for low initial surface cover values whereas for areas with high initial surface cover, the effect of changes in precipitation dominate the formation of landscapes. This study demonstrates a sensitivity of catchment characteristics to different transient forcings in vegetation cover and mean annual precipitation, with a crucial role for initial vegetation and climate conditions. Ongoing research is developing fully-coupled landscape evolution and dynamic vegetation model (see companion paper) forced with predicted paleoclimate histories from an atmospheric general circulation model.