Modeling the sensitivity of sediment and water runoff dynamics to Holocene climate and land use changes at the catchment scale

An increasing number of studies have indicated that soil erosion, sediment redistribution and water discharge during the Holocene have varied greatly under influence of environmental changes. In this paper we have used a modeling approach to study the driving forces for soil erosion and sediment redistribution on the one hand, and water discharge on the other hand, during the Holocene for the Belgian Dijle catchment.Soil erosion and sediment redistribution was modeled using the spatially distributed Watem/Sedem model. Several scenarios of past land use and climate were used to model soil erosion, colluvial sedimentation and sediment export to the fluvial system, and those scenarios were combined with a sensitivity analysis. Modeling results are validated based on an available time differentiated field-based sediment budget. Water discharge was modeled using the spatially distributed STREAM model with a daily time step. The model was calibrated based on contemporary discharge data. The results indicate that soil erosion has increased between the early Holocene and the current situation by ca. 9% due to climatic variations, and by ca. 6000% due to changes in land use. The average discharge has increased by ca. 7%, mainly due to land use changes, and the discharge also shows more peaks. The decrease in cropland area and increase in built up area since 1775 CE has resulted in a decrease in soil erosion and in a further increase in discharge, showing the difference in sensitivity of both processes to land use changes.