拉萨河冬季径流对气候变暖和冻土退化的响应

Hydrological Response of Lhasa River to Climate Change and Permafrost Degradation in Xizang

20世纪90年代以来,拉萨河流域的气温经历了10年升高0.54oC的气候变暖,这期间以秋冬季升温为主。在近40年(1963￣2004年)气候和28年(1976￣2004年)月径流数据的基础上,研究了具有多年冻土的高海拔拉萨河流域的冻土和水文响应。结果表明,冬季径流对11￣2月气温升高具有显著响应,在12￣2月份增加了16%,其中2月份增加22%。水热相关分析表明,10￣11月地表温度升高0.8￣0.9oC导致冬季河流水量增多,介于0.9￣1.5m深度的季节冻土深度和温度变化导致了径流量变化的响应。20世纪90年代的气候变暖使得多年冻土区的季节冻土深度萎缩了大约14cm,冻土区的冬季径流水文响应比气温更快、更显著。但冻土积雪观测的不足使冬季水文变化具有不确定性。

Air temperature in the Lhasa River basin has increased by 0.54℃ since 1990, particularly in winter and autumn, while precipitation did not increase in the same period. Based on climatological data of （1963-2003） and monthly runoff data of 28 years （1976-2004）, the hydrological and geocryological response to the climate change was studied. The significant response to the temperature rising from the winter streamflow during November to February was detected, winter streamflow during December to February increased by 16% and in February by 22%. Correlation analysis between water flow and temperature indicated that the rise in temperature in October and November by 0.8-0.9℃ resulted in the increase in winter streamflow, the seasonal frost at depth of 0.9-1.5 m became thinner comparing with that before the 1990s, the thickness decreased by about 14 cm. The hydrological response from winter flow in a permafrost basin is more sensitive and quicker than that of air temperature. There are un-certainties due to the lack of both soil frost and snowfall survey on the Tibetan Plateau.