Observations of drop size distributions in natural rainfall have shown that the range of drop sizes increases with increasing rainfall intensity. If a network of nozzles is used to generate artificial rainfall, an increase in working pressure increases the average intensity but decreases the range of drop sizes within the spray. This property has hindered the development of the rainfall simulator more than any other single factor. Alternative methods of simulating rainfall, which depend upon individual drop forming elements such as hypodermic needles for example, are capable of producing sprays with uniform drop sizes only. Such methods have been employed successfully in generating storm patterns involving both temporal and spatial variations in intensity for laboratory catchment studies. A general purpose rainfall simulator, combining control of application rates in both space and time with the reproduction of the drop size distributions and velocities of fall of drops observed in nature, has yet to be developed.