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Study on the differences in water vapour characteristics and predictive signals of low‐frequency precipitation in the pre‐flood season of South China between flood and drought years

Using 753 station's precipitation daily data in China and NCEP/NCAR daily reanalysis data from 1980 to 2017, the lead–lag correlations between 10 and 20 days low‐frequency (LF) precipitation and LF water vapour transport are comparatively analysed in the pre‐flood season of South China during typical flood and drought years, and verified using Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) backward trajectory model. The same features during both the flood and drought years include that, (a) the primary LF water vapour sources are the south side of Lake Baikal, the northern Sea of Japan and the Yellow Sea, the South China Sea and the western Pacific Ocean. (b)The key LF water vapour circulation systems are the Lake Baikal anticyclone (LBAC), the Northeast China cyclone (NECC), the Philippine Sea anticyclone (PSAC) and the South China cyclone (SCC). The different features between the flood and drought years include that, (a) the southern Sea of Japan is another water vapour source and the Australia anticyclone (AAC) is another key LF water vapour circulation system in the flood years. (b) There are two southwest warm water vapour flows and one southeast cross‐equatorial water vapour flow in the flood years, while there is only one southwest warm water vapour flow in the drought years. In addition, most of notable predictive signals start appearing at approximately −4 days in both the flood and drought years. However, there is a difference in the time of occurrence of similar predictive signals, and some predictive signals only appear in the flood years.