Analysis of climate and vegetation variability on erosion using a
coupled dynamic vegetation and landform evolution model
Abstract
Variability in precipitation frequency, intensity and duration deeply
affect vegetation and erosion yields. Under climate change scenarios,
alterations in precipitation are expected but it is not well understood
how it could affect erosion rates and what is the role of vegetation on
landscape geomorphic response. Traditional erosion models normally
include basic representations of vegetation that do not account for the
dynamic character of biomass variability and feedbacks with hydrological
and erosion/deposition processes. Hence, using a new modelling
frameworks that account for the effect of varying vegetation cover on
erosion, and that includes climate change scenarios is needed. Here we
use a new model: COPLAS, a tool that couples a Landform Evolution Model
with dynamic vegetation and carbon pools modules to investigate the
response of landscapes to climate change. The vegetation module includes
a coupled photosynthesis-stomatal conductance representation that
responds to climatic data inputs as temperature, CO2 concentration and
water availability. We use the model to simulate the erosional and
geomorphic responses of dynamic vegetation in Howard Springs (Australia)
to predicted changes in daily precipitation under future CO2
concentrations of about 940 ppm. The model was calibrated using Ozflux
site historical data. Catchment scale simulations were run for a period
of 100 years for three scenarios (bare soil, constant and dynamic
vegetation) using a daily time step. We found that, for our study case,
bare soil produces on average 139% more erosion than the constant
vegetation case and 124% more than the dynamic vegetation case.
Moreover, an increase in precipitation of around 23% induces an
increase of 25%, 35% and 43% in the erosion rates for dynamic
vegetation, constant vegetation and bare soil respectively, while a
decrease in 26% reduces it in 36%, 60% and 59%. This could be
explained by the nonlinear relation between erosion and vegetation
(higher rainfall induces higher erosion potential which can be
counteracted by an increase in vegetation cover leading to a decrease in
soil erodibilty). This finding highlights the importance of considering
the dynamic character of vegetation in order to understand the nonlinear
relations between fluvial erosion and vegetation cover.