印度季风活动导致青藏高原夏季降水稳定氢氧同位素出现突变特征。因此，通过这种突变特征可以定性描述甚至定量揭示印度季风的活动规律。本项目拟以喜马拉雅山南北坡四个跨境剖面上8个核心站点和8个参考站点为平台，分别同步采集历次降水样品，测定降水稳定氢氧同位素，利用逆推空气轨迹方法，建立水汽追踪模型，分析不同水汽来源对降水稳定同位素变化的影响，并结合LMDZ-iso同位素模型模拟，揭示喜马拉雅山南北坡稳定同位素时空变化特征，建立其对气象（温度、降水量等）及海拔高度等因子的响应模式及其现代过程的分馏模式。尤其是，根据高精度的稳定同位素日变化序列，揭示其对印度季风活动的响应，从而定量探讨印度季风在喜马拉雅山南北坡爆发与撤退的具体日期。这对于该研究区域农业、旅游业及牧业的生产（或发展）都具有重要的指示意义。而且，深入了解高山地区的降水稳定氢氧同位素，可以为进一步揭示局地水循环的过程与机制提供理论基础。

Stable hydrogen and oxygen isotopes of summer precipitation over the Tibetan Plateau abruptly deceased due to the influences of the Indian monsoon. Hence, the variability in the dates of the Indian monsoon onset and retreat on the southern and northern slopes of the Himalayas can be determined by precipitation stable isotopes. Based on eight key stations on the southern and northern slopes of the Himalayas and eight reference stations on the adjacent regions, this project will focus on stable hydrogen and oxygen isotope variations in precipitation at the event scale. We will collect simultaneous precipitation samples at different stations, then measure stable hydrogen and oxygen isotopic compositions of all samples, analyze the impact of the moisture sources upon the variations of stable isotopes in precipitation, based on the backward trajectory model. In addition, we will reveal the temporal and spatial distribution of stable hydrogen and oxygen isotopes in precipitation, and obtain the relationships between precipitation stable isotopes and climatic information (such as air temperature, precipitation amount, etc.) and elevation factor, in combination with the LMDZ-iso simulation which is suitable for the Tibetan Plateau. In particular, this project attempts to develop criteria for understanding the onset and retreat of the Indian monsoon across the central Himalayas, using precipitation stable isotopes. It will provide a good insight for better guidance of agricultural production, tourist activities, and vegetative activities, for the dates of onset and retreat of the Indian monsoon are critical for farmers in the south of the Himalayas, tourist in the Himalayas, and herdsmen in the north. In addition, understanding the stable isotope composition of precipitation over the high and large mountainous regions is helpful to provide data set for the study of the local water cycle.