Changes in Vegetation, Climate Elements, and Runoff of Yarlung Zangbo RiverBasin

As a crucial water resource and hydropower strategic reserve area in China,the Yarlung Zangbo River is also an extremely sensitive region to climate change, whose water cycle is of great  significance to research on climate change response and the planning and utilization of regional hydropower resources. Based on a gridded daily observation dataset over China and monthly runoff data at Nuxia Station, variation characteristics of multi-scale hydrometeorological elements were investigated and the response of runoff to climatic elements on different time scales were analyzed, combining methods including linear regression, Mann-Kendall test, Pettitt mutation test and partial correction analysis.The results demonstrate that the leaf area index (LAI) of forest vegetation in the basin above the Nuxia Station has increased significantly, while which of other vegetation types has remained stable. Both precipitation and runoff exhibit insignificant upward trends, with abrupt changes occurring in 1997. After the abrupt change, spring precipitation and winter runoff displayed the largest amplitudes of change compared to other seasons, with increases of 19.9% and 22.1% respectively. Temperature has increased significantly at a rate of 0.3°C per decade, showing a significant upward trend on different time scales. Moreover, the increasing trend of minimum temperature is grater than that of maximum temperature. The warming rate in winter reaches 0.38°C/10a, followed by autumn, while summer demonstrates the smallest increase. Regarding the intra-annual distribution, precipitation is relatively abundant in summer, accounting for 64.2% of total annual precipitation, whereas winter precipitation is scarce, contributing only 3.3%. The annual distribution of precipitation is uneven. Runoff changes are consistent with precipitation, mainly concentrated from June to September during the flood season. The uneven distribution coefficients of precipitation and runoff have gradually decreased, manifesting that the intra-annual distribution tends to be more even. Correlation analysis indicates that the precipitation is the main factor which affects the annual runoff due to the fact that the correlation coefficient between precipitation and runoff is 0.79 at the annual scale. The dominant factors driving runoff changes are heterogeneous across different time scales. The process of intra-annual runoff distribution is governed by the combined effects of temperature and precipitation.