喜马拉雅山北坡卡鲁雄曲径流与气候变化

以冰川融水补给为主的喜马拉雅山北坡的卡鲁雄曲流域,近20年平均气温以0.34 ^oC/10a的趋势上升,高于西藏年均温0.26 ^oC/10a的增长率,更是明显高于全国和全球气温的增长率,且极端最高温都出现在20世纪90年代。后10年气温 (1994~2003年) 比前十年 (1983~1993年) 升高0.5 ^oC,径流量增加了26%;不同月份径流增加强度不同,10~2月增加了44%,7~9月增加了27%,3~6月增加了24%。径流对气候变化的响应最灵敏 (一年中有8个月的增加趋势通过了α = 0.05的显著性检验),尤其是秋冬季的径流 (增加趋势超过α = 0.01的显著性检验)。受冰川消融和季风影响,不同时期的径流有不同的影响因素,但存在共性,即气温对径流起着积极主导作用,而降水对径流的影响具有不确定性,即正负双面效应。     

喜马拉雅山北坡典型高山冻土区冬季径流过程

喜马拉雅山北坡广泛分布着岛状多年冻土，冻土对径流过程有着不可忽视的影响。卡鲁雄曲是该区唯一有常规水文气象观测资料的流域，海拔范围是4 550~7 200 m，其中5 100 m以上为高山冻土区，以下为深层季节冻土区。近20年径流有较明显的增加趋势，为了探明引起径流变化的原因，采用流域内翁果水文站1983—2003年的月径流资料，通过Mann Kendall趋势检验法，Sen坡度估计以及相关统计分析方法，发现寒冷期（11月至次年3月）径流有不同程度的涨幅，发生突变的年份在1990年左右。尤其以1月份最为明显，后10年比前10年增加了67%。遥相关分析表明，1月份径流与7~12月径流有通过95%显著性检验的相关性，它们的共同作用使得径流变化尤为显著，这是冻土区所特有的。     

1956-2003年拉萨河流域径流变化趋势

Taking the Lhasa River Basin above Lhasa hydrological station in Tibetan Plateau as a study area, the characteristics of the annual and monthly mean runoff during 1956-2003 were analyzed, based on the hydro-data of the two hydrological stations （Lhasa and Tanggya） and the meteorological data of the three meteorological stations （Damxung, Lhasa and Tanggya）. The trends and the change points of runoff and climate from 1956 to 2003 were detected using the nonparametric Mann-Kendall test and Pettitt-Mann-Whitney change-point statistics. The correlations between runoff and climate change were analyzed using multiple linear regression. The major results could be summarized as follows： （1） The annual mean runoff during the last 50 years 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 monthly mean runoff with a positive trend is centralized in winter half-year （November to April） and some other months （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 season.