江河源区位于青藏高原腹地， 是东亚气候变化的敏感区之一， 研究水汽的分布、 输送及收支对于理解区域降水特征具有重要意义。本研究基于1980 -2019年欧洲中期天气预报中心（ECMWF）的ERA5再分析资料， 结合1981 -2010年国家气象科学数据中心9个探空站资料， 分析了江河源及其毗邻地区水汽分布、 输送及各边界水汽收支的时空演变特征。结果表明： 江河源及其毗邻地区水汽含量的空间分布差异较大， 呈现出东南高、 西北低的特征。不同季节水汽含量分布及量值也不同， 表现为夏季最大， 秋、 春季次之， 冬季最少。源区及雅鲁藏布江流域水汽含量的年循环呈单峰变化， 主要集中在6 -8月， 最大值出现在7月（41.6 mm）， 年际变化呈增加趋势， 增速为0.4 mm·（10a）^-1。江河源区水汽通量主要来自阿拉伯海和孟加拉湾， 其次是中纬度西风以及西北气流的输送， 三种气流在雅鲁藏布大峡谷形成明显的水汽辐合， 不同季节水汽输送强度存在一定差异。在水汽的输入边界中， 西边界输入量最大（815.3×10⁶ kg·s^-1）， 南边界（724.9×10⁶ kg·s^-1）次之， 且两个边界季节变化显著； 北边界（317.9×10⁶ kg·s^-1）输入较少， 而东边界是水汽通量的输出边界， 最大水汽输出在9月（140.5×10⁶ kg·s^-1）。江河源区净水汽输入量大于输出量， 水汽通量呈盈余状态， 这将进一步影响江河源区降水及区域水循环的变化。

The Source Region of the Three-River （SRTR） lies in the hinterland of the Qinghai-Xizang （Tibetan） Plateau （QXP） and is one of the sensitive regions to climate change in East Asia.It is of great significance to study the distribution， transport， and budget of water vapor for understanding the characteristics of the regional precipitation.This research is based on the ERA5 reanalysis data of the European Centre for Medium-Range Weather Forecasts （ECMWF） from 1980 to 2019， combined with the data of 9 radiosonde stations in the National Meteorological Data Center from 1981 to 2010.The temporal and spatial variation characteristics of water vapor distribution， water vapor transport flux and budget of each boundary over the SRTR and its surrounding areas are analyzed.The results show that there are significant differences in the spatial distribution of water vapor content， which presents a high value region in the southeastern QXP and a low value region in the northwest of the QXP.The distribution and value of water vapor content are different in four seasons， which exhibit the largest in summer， followed by autumn and spring， and the least in winter.The annual cycle of water vapor content manifests the single peak over the SRTR and the Brahmaputra River basin.Water vapor is mainly concentrated in June to August and its maximum appears in July with a value of 41.6 mm.The inter-annual variation shows an increasing trend with a rate of 0.4 mm·（10a）^-1.The Arabian Sea and the Bay of Bengal are the main sources of water vapor over the SRTR， followed by the western airflow from the middle latitude and the northwestern airflow.Three kinds of airflows form obvious convergence of water vapor transport flux over the Brahmaputra Grand Canyon.There are seasonal discrepancies in the intensity of water vapor transport.Among the water vapor import boundaries， the western boundary has the largest import （815.3×10⁶ kg·s^-1）， followed by the southern boundary （724.9×10⁶ kg·s^-1） and the seasonal variations of the two boundaries are significant.The northern boundary has less import （317.9×10⁶ kg·s^-1）， while the eastern boundary is the export boundary of water vapor flux， and the maximum water vapor export is in September with a value of 140.5×10⁶ kg·s^-1.The net water vapor import is greater than the export， thus the water vapor flux is in surplus， which is about to affect the variations of precipitation and the regional water cycle over the SRTR.