Trend Analysis of the Runoff Var iation in Lhasa River Basin in Tibetan Plateau during the Last 50 Years
拉萨河流域近50 年来径流变化趋势分析

Taking the Lhasa River Basin above Lhasa hydrological station in Tibetan plateau as a study objective, the characteristics of the annual and monthly mean runoff in 1956-2003 were analyzed, which were based on the hydro-data of the two hydrological stations (Lhasa and Tangga) and the meteorological data of the three meteorological stations (Damxung, Lhasa and Tangga). The trends and the change-points of runoff and climate from 1956 to 2003 were detected by using the nonparametric Mann-Kendall test and Pettitt-Mann-Whitney change-point statistics. The correlations between the runoff and climate change were analyzed by using multiple linear regression. The major results could be summarized as follows: (1) The annual mean runoff in 1956~2003 is characterized by a great fluctuation and a positive trend with two change-points (around 1970 and the early 1980s), after which the runoff tended to increase and was increasing intensively in the last 20 years. Besides the annual mean runoff, the monthly mean runoff with a positive trend is in winter half year (from November to April) and summer half year (May, July and September). (2) The trends of the climate change in the study-area are generally consistent with the trend of the runoff, but the leading climate factors which aroused the runoff variation are distinct. Precipitation is the dominant factor influencing the annual and monthly mean runoff in summer half year, while temperature is the primary factor in winter.