A simulation model for desert runoff and erosion.

A distributed hillslope hydrological model is presented for a slope profile strip of variable width. It is based on stores representing soil moisture in an irregular bedrock surface, partially or entirely covered by a colluvial and/or wind-blown regolith. The model is used to explore the variations in infiltration, overland flow, soil moisture and evapotranspiration in response to differences in rainfall totals and storm durations, in gradient and in regolith depth and uniformity. Infiltration is separately estimated for bedrock and regolith components with evapotranspiration estimated from local soil moisture storage, and therefore persists longer in areas with only partial regolith cover. Biological activity is related to storage and evapotranspiration rates. Overland flow is routed downslope as a one-dimensional kinematic wave. The model is also used in aggregate form for longer periods to estimate erosion by overland flow. Some inferences are drawn about the extent to which differences between Sde Boker and the Hovav plateau are due to differences in climate, or to differences in local relief and in the supply of wind-blown sediment. (A)