Effect of changing vegetation and precipitation on denudation – Part 2: Predicted landscape response to transient climate and vegetation cover over millennial to million-year timescales

摘要

We present a numerical modeling investigation into theinteractions between transient climate and vegetation cover with hillslopeand detachment limited fluvial processes. Model simulations were designed toinvestigate topographic patterns and behavior resulting from changing climateand the associated changes in surface vegetation cover. The Landlab surfaceprocess model was modified to evaluate the effects of temporal variations invegetation cover on hillslope diffusion and fluvial erosion. A suite ofsimulations were conducted to represent present-day climatic conditions andsatellite derived vegetation cover at four different research areas in theChilean Coastal Cordillera. These simulations included steady-statesimulations as well as transient simulations with forcings in either climateor vegetation cover over millennial to million-year timescales. Two differenttransient variations in climate andvegetation cover including a step change in climate or vegetation were used, as well as100 kyr oscillations over 5 Myr. We conducted eight different step-changesimulations for positive and negative perturbations in either vegetationcover or climate and six simulations with oscillating transient forcings foreither vegetation cover, climate, or oscillations in both vegetation coverand climate. Results indicate that the coupled influence of surfacevegetation cover and mean annual precipitation shifts basin landforms towardsa new steady state, with the magnitude of the change being highly sensitive to theinitial vegetation and climate conditions of the basin. Dry, non-vegetatedbasins show higher magnitudes of adjustment than basins that are situated inwetter conditions with higher vegetation cover. For coupled conditions whensurface vegetation cover and mean annual precipitation change simultaneously,the landscape response tends to be weaker. When vegetation cover and meanannual precipitation change independently from one another, higher magnitudeshifts in topographic metrics are predicted. Changes in vegetation cover showa higher impact on topography for low initial surface cover values; however,for areas with high initial surface cover, the effect of changes inprecipitation dominate the formation of landscapes. This study demonstratesthe sensitivity of catchment characteristics to different transient forcings invegetation cover and mean annual precipitation, withinitial vegetation and climate conditions playing a crucial role.