Abstract: Arid regions are often far from sea and ocean, the patterns of supply of water vapour to heavy rain area are generally different from those in humid regions. Several major patterns were summarized and the effect of precursory light rain on the following heavy rain process, the effect of low-level easterly wind on the occurrence of heavy rain, the role of advected (external) moisture, and especially the importance of recycled (internal) moisture in south Xinjiang were also discussed