Abstract: A method and apparatus are provided for conducting meso-scale rainfall simulations and runoff collections. The apparatus includes a system for continuously applying to a test plot simulated rainfall having a droplet size spectrum, an impact velocity, a spatial uniformity and an intensity simulating natural rainfall. Additionally, the apparatus includes a collector assembly for collecting runoff from the test plot for analysis. In accordance with the present method, natural rainfall for a geographic area including the test plot is studied in order to determine the drop size spectrum, drop impact velocity, spatial uniformity and intensity of the rainfall. A sprayer or irrigation head is then selected providing a droplet size spectrum closely resembling that of the natural rainfall to be simulated. Next, the spacing between and relative height of the irrigation heads is adjusted to ensure that the spatial uniformity, intensity and drop impact velocity resemble that of the natural rainfall to be simulated.