The characteristics of moisture transport associated with drought/flood in summer over the east of the southwestern China

Based on the NCEP/NCAR reanalysis monthly data and daily precipitation data for the 20 stations in the east of the southwestern China from 1959 to 2006, the characteristics of moisture transport associated with drought/flood in summer over the east of the southwestern China have been analyzed. The results show that there are two main water vapor paths directed to the area of the east of the southwestern China. One comes initially from the Tibetan Plateau and then turns toward the Bay of Bengal and reaches the east of the southwestern China through Burma and Yunnan province. The other comes from the south of the Bay of Bengal with the strong vapor transport band directed to the IndoChina Peninsula and the South China Sea merging with crossing equator vapor therein. The moisture turning north from south of Western Pacific Subtropical High (WPSH) contributes also to the east of the southwestern China. The intensity of the Indian Ocean Vapor Path (IOVP) is the strongest, and the one of the Pacific Ocean Path is the weakest associated with vapor transport in the east of the southwestern China. The intensity of the Tibetan Plateau Southern Side Path is far less than that of the IOVP in the Indian Ocean monsoon area. Over the Eastern Asian monsoon area the meridional moisture transport is stronger than the zonal one, whereas the zonal vapor transport is stronger than the meridional one over the Indian Ocean area. The summer rainfall in the east of the southwestern China is connected closely with changes in the zonal moisture transport, but there is no obvious relationship between this rainfall and changes in the meridional one. The precipitation over the east of the southwestern China is more prone to flood in case the water vapor transport of the southern IOVP is weak when the strong moisture transport of by the northern Indian and the eastern Asian monsoon result in the transport direction becoming more longitudinal over the Indian monsoon zone while becoming more latitudinal over the eastern Asian area, which causes the whole water vapor transport band tend to be more western, and conversely it tends to drought. Over the area the east of the southwestern China thereare a net outcome in summer, and it is a weak water source with the most income entering through its southern border. In drought years the vapor flowing out is more dramatic than normal whereas in flood years there is weak net outcome. There is closely relationship of the vapor transport intensity with the 500 hPa and SST patterns.