Climatic Characteristics of Runoff Variation in Flood Season in Jinsha River Basin

As one of the largest rivers in southwestern China, Jinsha River is rich in water resources and hydropower resources, but at the same time, it is also an important flood zone over the upper and middle reaches of Yangtze River in flood season. Therefore, water resource as well as flood and drought changes in this region play a prominent role in the temporal and spatial distribution of water resources in China. In this paper, the data of runoff from four stations in Zhimenda (1957-2002), Shigu (1952-2004), Xiaodeshi (1953-2005) and Pingshan (1940-2004) hydrological stations, NCEP/NCAR reanalysis data and precipitation dataset from gauge stations were collected. Besides, by using trend analysis, correlation analysis, wavelet analysis and sliding-t test and other methods, the climatic characteristics of runoff variation in flood season (July-September) over Jinsha River were studied. The results show that: the annual variation trend of runoff is not significant in flood season; the runoff in Zhimenda station takes a time scale of 2~4 years as the main oscillation cycle; the significant abrupt change of runoff is found around 1970 in Shigu, Xiaodeshi and Pingshan stations; before 1970, the main oscillation period is of a 2~4 years time scale, while after 1970, it is of a 8-16 years time scale; the runoff change in the downstream of Jinsha River Basin is dominated by the runoff in the upper and middle reaches of the mainstream of Jinsha River and its branchs; when the westerly vapor transport over the regions from Iranian plateau to the central and western Tibetan plateau is strengthened (weakened), the precipitation over the Three Rivers Source Region increases (decreases), which is benefit for the increase (decrease) of runoff in the source of Jinsha River; when the westerly vapor transport along the south edge of Tibetan plateau and the northeasterly vapor transport which comes from the west side of the cyclonic moisture transport circulation are strengthened (weakened), the precipitation along the upper reaches of Jinsha River and the middle and lower reaches of Yalong River increases (decreases), which result in the increase (decrease) of runoff over the middle and lower reaches of Jinsha River.