Rain belts in East Asia frequently pose threats to human societies and
natural systems. Advances in a skillful forecast on heavy precipitation
require a deeper understanding of the preconditioned environments and
the hydrologic cycle. Here, we disentangle 15 dominant moisture channels
along four corridors reaching the Somali Jet, South Asia, Bay of Bengal
and Pacific basin for the warm-season rain belts. Among them, the Somali
and South Asian channels were underappreciated in the literature. The
results also highlight the importance of terrestrial moisture sources
and the close relationship between the moisture pathways and rain belts'
characteristics. Back-tracing the weather within a 2-week lead time
reveals the pre-existing weather systems and circumglobal wave trains
that govern the moisture channels. Findings from this work develop a
better understanding of East Asian rain belts' water cycle and may offer
insights into model evaluation and heavy rainfall prediction at a longer
lead time.