Features and Sources of the Anomalous Moisture Transport for the Severe Summer Rainfall over the Upper Reaches of the Yangtze River

Using the daily NCEP/NCAR reanalysis dataset and the observation rainfall data in China for the 1980-1997 period, features of severe summer rainfall over the upper reaches of the Yangtze River are investigated and then sources of moisture contributing to severe rainfall over eastern and western Sichuan Province (ES and WS for short) are examined with particular reference. It turns out that the severe rainfall occurring locally dominates summer rainfall over the upper reaches of the Yangtze River. Climatological rainfall and anomalous one constitute severe rainfall, but the latter accounts much for severe rainfall. The meridional moisture transport dominates the composite moisture transport on the occurrence day for ES region, while the zonal is equivalent to the meridional for WS region. Correlation between the moisture transport fluxes over the two regions of severe rainfall and other regions, the anomaly and variation of the moisture transport day by day during the period of severe rainfall lend a support for the conclusion that the meeting of the moisture from the West Pacific through the South China Sea (SCS) and the one from northwestern China exerts a vital effect on the occurrence of severe rainfall, which can not be neglected.