Water Vapor Transportation over China and Its Relationship with Draught and Flood in the Yangtze River Basin
中国地区水汽输送异常特征及其 与长江流域旱涝的关系

The characteristics of water vapor transportation over China and its relationship with precipitation anomalies in the Yangtze River Basin are analyzed by using the observed data in China and ECMWF reanalysis data from 1981 to 2002 in summer. The results indicate that the first mode of the integrated water vapor transportation is significant whose spatial distribution presents water vapor convergence or divergence in the Yangtze River Basin, and whose variation has a close relationship with the precipitation in the Yangtze River Basin. When the Western Pacific Subtropical High (WPSH) is strong and shifts southward and westward, the Indian Monsoon Low Pressure (IMLP) is weak, and the northern part of China stands behind of the middle and high latitude trough, a large amount of water vapor from Bay of Bengal (BOB), South China Sea (SCS) and Western Pacific forms a strong and steady southwest water vapor band and meets the strong cold water vapor from northern China in the Yangtze River Basin, thus it is likely to cause flood in the Yangtze River Basin. When WPSH is weak and shifts northward and eastward, IMLP is strong, and there is nearly straight west wind over the middle and high latitude, it is unfavorable for oceanic vapor extending to China and no steady and strong southwest water vapor transportation exists in the region south of the Yangtze River. Meanwhile the cold air from northern China is weak and can hardly be transported to the Yangtze River Basin. This brings on no obvious water vapor convergence and less precipitation in the Yangtze River Basin.