气候变化背景下流域陆面过程与径流发生变化，极易造成极端水文事件包括洪涝与干旱等，严重威胁着人类生命财产的安全。尤其对于作为河流源区的高寒地区，径流来源成分及驱动力研究在流域水安全建设过程中起到重要作用。我国青藏高原地区十分典型，受制于实测数据匮乏，当前关于该地区径流成分解析研究仍旧不足。本研究以位于青藏高原腹地的国际河流雅鲁藏布江流域（以下简称雅江流域）为研究区，定量评估了该流域冰川径流对天然径流量的贡献，结合植被覆盖度指数对雅江流域出口径流的影响进行了分析，并探讨了极端气候对雅江流域径流变化的影响。最后，结合未来气候模式模拟分析了雅江流域未来水文要素变化。主要结论有：

（1）本研究提出了一种基于冰川厚度的冰川储量计算方法，得到了雅江流域在RGI 4.0和GIC-Ⅱ两次冰川编目中的冰川储量数据。结合人类活动用水量对雅江流域出口站径流进行了还原计算，基于还原得到的天然径流量，解析出冰川径流量对总径流量的贡献率介于4%~8%之间。基于普适性气体状态方程构建了新的冻土算法，获取了流域内土壤含水率时空分布数据集，并演算得到冻融过程在流域出口产生的径流量，其对天然总径流量的贡献率由上世纪90年代前的5%左右下降到本世纪初不足2%。

（2）分析雅江流域内植被覆盖度指数（Normalized Difference Vegetaion Index，NDVI）变化规律，表明其总体随高程增加呈线性减少态势，且3767m以下地区NDVI分布主要由高程主导，3767~5051 m区域NDVI变化主要受降水量多寡制约。关于流域内土地利用方式转变，1980~1990年间雅江流域土地利用类型以自然更替为主，而1990~2000年人为因素扰动较强；期间流域平均NDVI变化与径流变化具有显著的相关性，径流变化较NDVI变化存在2~5个月的滞后期，在一定程度上NDVI会起到减小出口流量的作用。

（3）通过分析雅江流域内极端气温变化特征，发现其极端气温事件总体呈增多态势。结合大气环流因子变化研究，得知北大西洋涛动（North Atlantic Oscillation，NAO）与雅江流域内极端气温关联显著，且当NAO由正相态逐渐减弱并向负相态转变时，冷季极端气温显著增加。西风、发源于地中海域的Rossby波列以及促进Rossby波列向我国传播的群风均是NAO影响我国冷季极端气温的潜在路径。另外，分析极端水文事件变化特征，发现其具有持续性，极端降水因子和极端气温因子分别在极端洪水事件变化和极端枯水事件变化中占主导作用，且极端降水对雅江流域极端水文事件影响强于极端气温的影响。

（4）模拟雅江流域未来水文过程结果显示，径流变化与降水量变化具有极强的一致性，从近期来看二者呈下降态势，而远期二者均表现为增加态势。径流季节性十分明显，春季径流显著增加，这与气候变暖背景下流域内冰川、积雪、冻土消融不无关联。

Land surface processes and runoff in rivers are changing under the background of climate change. Extreme hydrological events such as floods and droughts are increasing, which pose a great threat to humankind and society. Particular in headwater area of the alpine region, studies on runoff evolution and driving factors play a significant role for water-security. As the most typical region in China, studies on the runoff evolution in the Qinghai-Tibetan Plateau are still not enough due to the deficiency of in-situ data. The Yarlung Zangbo River basin, located in the Tibetan Plateau, was selected as the study area in this dissertation. In this study, the contribution of glacier runoff to the total runoff was identified. The impact of NDVI on runoff was investigated. Then the effect of extreme climate on extreme hydrological events in the Yarlung Zangbo River basin was analyzed. Finally, changes of future hydrological processes were simulated with the combination of GCM. The results can be concluded as follows.

(1) A glacier thickness-dependent algorithm was proposed to estimate the glacier volume based on elevation datasets and other data. Natural runoff was estimated with the consideration of water consumption. At an annual scale, glacier-melt runoff accounts 4%~8% for the total runoff. A new frozen-soil algorithm was proposed on the basis of the ideal gas state equation. The spatial and temporal distribution of soil moisture in the study area was then obtained. The contribution of outlet runoff produced by freezing-thawing processes to natural runoff was around 5% before 1990s, while the rate decreased to less than 2% in the 2000s.

(2) In general, NDVI decreased linearly with the increase of elevation. The distribution of NDVI was classified by the elevation bands of 3767 m and 5051 m. The elevation rules the distribution of NDVI in the area under 3767 m, whereas in the 3767~5051 m, NDVI was mainly controlled by precipitation. The analysis on land use changes indicated that the natural variation was the main way in the study area. During 1990~2000, the land degradation by human disturbance was significant. In this duration, changes of runoff were significantly related to NDVI variation. Runoff variation laged around 2~5 months (mainly 3~4 months) to the change of NDVI. The vegetation cover condition resulted in the decrease of outlet runoff in some extent.

 (3) Extreme temperature events were increasing in the study area. In combination with atmospheric circulation factors, NAO (North Atlantic Oscillation) was found to be the closest relationship with extreme temperature. When NAO weakened from normal phase to negative phase, extreme temperatures in cold season significantly increased. In the process, westerlies, Rossby wave train originated from Mediterranean, and group wind forwarding Rossby wave train to China were potential paths. In addition, the Hurst indexes of extreme hydrological events were within 0.62~0.63 illustrating the continuity. Extreme flooding events and extreme drought events were dominated by extreme precipitation and temperature, respectively, in which extreme precipitation showed a great influence on extreme hydrological events.

(4) The simulation of future hydrological processes in the Yarlung Zangbo River basin showed that runoff varied with precipitation. Both are reducing from 2006~2020 to 2046~2060, while increasing from 2046~2060 to 2086~2100. The seasonality was obviously obtained in runoff. The spring runoff significantly increases due to the melting snow, glaciers and frozen soils.