Also known as relief rainfall, this forms when moisture-laden air masses are forced to rise over high ground. The air is cooled, the water vapour condenses, and precipitation occurs. See Gray and Seed (2000) Meteorol. Applics. 7 on the characterization of orographic rainfall, and Minder et al. (2008) Qly. J. Royal Met. Soc. 134, 633, 817–39, Part B, on small-scale patterns of mountain precipitation. The step-duration orographic intensification coefficient method may be used to estimate the effects of topography on storm rainfall; see Lin (1989) Atmospheric Deposition, IAHS Publ. 179.