AGU Fall Meeting, District-Of-Columbia, United States Of America, 10 - 14 December 2018, pp.5206
Landscapes are shaped by the interplay between the erosive power of runoff and the protective effect of vegetation against erosion. Climate change results in changes in both runoff production and vegetation cover, and these have counteracting effects. The delicate balance between both effects is more pronounced in water-limited ecosystems due to the tight dependency of vegetation growth on water availability. The nonlinear character of climate-vegetation interactions in semi-arid regions challenges our interpretation of the erosional response of landscapes. To elucidate the role of climate change on sediment export, we use the CHILD landscape evolution model coupled with vegetation dynamics and surface hydrology in a semiarid Southwest US setting. The climate forcing was represented with a constant climate. In the first setting (dry-to-wet), mean annual precipitation (MAP) is increased from 200 mm to 600 mm; in the second one (wet-to-dry), used to compare the erosional response, MAP is decreased from 600 mm to 200 mm. Landform evolution and erosional response were investigated for bare soil and dynamic vegetation conditions. Results show that the sediment yield is in-phase with climate forcing when the surface is bare, and therefore an increase in precipitation leads to higher runoff production and higher sediment export. However, when vegetation dynamics is driven by climate, sediment production becomes out-of-phase with climate. In this case, erosion increases during dry periods and topography builds up during wet periods. This reversed behaviour is driven by the protective effect of vegetation cover that increases (decreases) due to vegetation growth (loss) during the wet (dry) periods, counteracting the contribution of increased (decreased) erosion due to runoff production. Another important outcome is the asymmetric temporal response of bare soil to the direction of climate change. In bare soil cases, the erosional response for dry-to-wet transitions is much faster than that of wet-to-dry transitions; however, this behaviour becomes symmetric for dynamic vegetation case.