Runoff Characteristics of the Nyangqu River Basin on the Qinghai-Tibet Plateau
青藏高原年楚河1961年至2000年的径流变化特征分析

Global climate change is gradually affecting the global and regional hydrology and water circulation. The Tibet-Qinghai Plateau is one of the most sensitive areas in response to global climate change. The Nyangqu River lies on the south of the Tibet-Qinghai Plateau. It is a tributary of the Brahmaputra River which is the largest river on the Tibet-Qinghai Plateau and western China. The Nyangqu River basin plays a fundamental role in this region since it hosts a relatively dense population and large areas of farmland. This river serves as the major sources of domestic and agricultural water use in this basin. In this paper, the authors focus primarily on runoff variation trends in the Nyangqu River during the period 1961-2000 and the characteristics of runoff in terms of periodicity and mutability. Based on annual runoff data during the period 1961-2000, the Mann-Kendall method and wavelet transform analysis were jointly adopted to unravel characteristics of runoff variations of the Nyangqu River. Results show that the annual change in the runoff of the Nyangqu River was relatively stable and the intra-annual distribution of the runoff was extremely uneven. In addition, the disparity in runoff between wet season and dry season was significant. The runoff from June to September accounted for 65% of that of the whole year, and the most monthly runoff accounts for 24.56%. During the period 1961-2000, the runoff showed a significant increasing trend and the runoff of the Rikaze station showed a more significant trend than that of the Gyangze station. The mutation of the runoff observed at the Rikaze station took place around 1985. After 1985, the runoff exhibited a notably increasing trend. Results of wavelet analysis show that a 5~8a oscillation period of the runoff was most notable and a 10-15a period was relatively notable. Principal periods of annual runoff at the Rikaze and Gyangze stations were found to be 5a and 7a, respectively. The secondary periods were 13a and 12a, respectively. Results of the Mann-Kendall test about the temperature and precipitation in the Nyangqu River basin showed that the mean temperature of the Nyangqu River basin had an increasing trend, but the precipitation remained fairly invariant. Increases in glacial melt water due to the rising temperature might be the principal reason for the increase in the runoff in the Nyangqu River.