Assessment of the impacts of dynamic soil properties and vegetation cover on soil erosion using distributed hydrological model

The challenges in soil erosion modeling are mainly attributed to the heterogeneity of the soil properties and the complex interactions between vegetation cover and soil erosion processes. Current process-based soil erosion models apply empirical adjustment factors to account for the influences of vegetation cover and land managements. Most of soil erosion models assume that the temporal changes of soil properties are negligible over temporal scale ranging from several days to decades. Physically meaningful model representations of soil erosion processes require deep understanding of the mechanisms through which vegetation cover influences the soil particles detachment and transport, as well as the temporal-spatial changes of soil properties. In this study, the dynamic changes of soil properties in soil erosion modeling were investigated, through a distributed soil erosion model (GEOTOP-erosion). Specifically, spatially distributed and dynamical soil variables are introduced into the soil erosion model. Soil particles associated with different grain sizes experience different transport processes. Soil textures and organic matter (OM) contents are updated daily according to the feedbacks on erosion and deposition processes. Other related soil properties are derived by the updated soil textures and OM contents. The influences of vegetation cover are represented by four major mechanisms: (1) modifying net rainfall and raindrop energy by canopy interception, (2) reducing runoff generation by transpiration, (3) retarding overland flow by increasing surface roughness, and (4) increasing soil cohesion by root system. The simulations of this soil erosion model show appropriate interactions between vegetation cover and soil erosion processes. The erosion process could also be dynamically adjusted by the evolution of soil properties. An experimental catchment in Ireland was selected to test the soil erosion model. The simulation results show a good agreement between estimated and observed soil loss in complex land surface conditions. The simulations incorporated dynamic soil properties demonstrate more accurate soil erosion simulation. The coupled model could be extended to more broad applications, such as evaluation of anthropogenic activities, estimation of influences of soil disturbances and long term soil evolution.