Sub-grid scale parameterization of hillslope runoff and erosion processes for catchment-scale models of semi-arid landscapes

The processes of hillslope runoff and erosion are typically represented at coarse spatial resolution in catchment-scale models due to computational limitations. Such representation typically fails to incorporate the important effects of topographic heterogeneity on runoff generation, overland flow, and soil erosion. These limitations currently undermine the application of distributed catchment models to understand the importance of thresholds and connectivity on hillslope and catchment-scale runoff and erosion, particularly in semi-arid environments. This paper presents a method for incorporating high-resolution topographic data to improve sub-grid scale parameterization of hillslope overland flow and erosion models. Results derived from simulations conducted using a kinematic wave overland flow model at 0.5m spatial resolution are used to parameterize the depth-discharge relationship in the overland flow model when applied at 16m resolution. The high-resolution simulations are also used to derive a more realistic parameterization of excess flow shear stress for use in the 16m resolution erosion model. Incorporating the sub-grid scale parameterization in the coarse-resolution model (16m) leads to improved predictions of overland flow and erosion when evaluated using results derived from high-resolution (0.5m) model simulations. The improvement in performance is observed for a range of event magnitudes and is most notable for erosion estimates due to the non-linear dependency between the rates of erosion and overland flow. Copyright (c) 2013 John Wiley & Sons, Ltd.