This paper describes the development and test of a numerical rainfall generator for use as a preprocessor for small-scale spatialized simulation of processes induced by rain, such as soil erosion or soil surface crusting. This generator produces series of individual raindrops respecting both a given hyetograph and a spatial distribution, and satisfying an imposed or parametrized size distribution, either to mimic the behavior of an experimental rainfall simulation or to reflect the properties of a natural rainfall. "Intensity maps" and "energy maps" can be used as inputs to take into account the spatial variability of the characteristics of rainfall produced by rainfall simulators, such as rainfall intensity or kinetic energy. The velocity and the shape of drops are estimated to permit an accurate evaluation of the effect of their impact on the ground and a solution to the problem of the partition of the volume of each drop on a discrete terrain is also proposed. Finally, comparisons are made with real data in order to validate the model.