Numerical simulation of the wind-driven rainfall distribution over small-scale topography in space and time

A general numerical simulation model is developed to determine the wind-driven rainfall (WDR) distribution over small-scale topography in space and time. It applies to the redistribution of rainfall by specific perturbed wind-flow patterns that occur over small-scale topography. The model is based on Computational Fluid Dynamics (CFD) and provides a necessary extension of the existing CFD models. It allows a high-resolution determination of the WDR distribution in both space and time. The model is demonstrated by application for a two-dimensional hill and a two-dimensional valley. The calculated distinct rainfall distribution patterns will be investigated and explained and the influence of different parameters will be analyzed in detail. It will be shown that the resulting variations in hydrologically effective rainfall can be very large (e.g. up to 92% in the examples analyzed). Therefore, these variations should be taken into account in e.g. catchment hydrology, runoff and erosion studies and the design of rainfall monitoring networks.