Characteristics of Water Vapor Transportation During Summer Heavy Rainfall at the Upper Reaches of Yangtze River in 1998

Using the ECMWF reanalysis data in summer of 1998, we analyzed the characteristics of water vapor transportation in the nine heavy rains taken place at the upper reaches of Yangtze River. The result shows that the water vapor of heavy rains at the upper reaches of Yangtze River mainly originates from Bay of Bengal, South China Sea and West Pacific, and sometimes the water vapor from north part of Arabian Sea can transport through the north part of India and southeast part of Tibetan Plateau which can contribute to the heavy rains. The source regions of the water vapor have an obvious difference between different heavy rains. Both the complex topography and the water vapor transportation ways at the upper reaches of Yangtze River are an important factor to determine the heavy rains. When the West Pacific Subtropical High is strong and shifts both to south and to west, and the Indian Monsoon Low Pressure is weak, there is a favor condition of water vapor transportation for the occurrence of heavy rains at the upper reaches of Yangtze River. The characteristics of the water vapor transportation also result in the complexity of the occurrence and development of heavy rains at the upper reaches of Yangtze River.