More than 1.4 billion people depend on water from the Indus, Ganges, Brahmaputra, Yangtze, and Yellow rivers. Upstream snow and ice reserves of these basins, important in sustaining seasonal water availability, are likely to be affected substantially by climate change, but to what extent is yet unclear. Here, we show that meltwater is extremely important in the Indus basin and important for the Brahmaputra basin, but plays only a modest role for the Ganges, Yangtze, and Yellow rivers. A huge difference also exists between basins in the extent to which climate change is predicted to affect water availability and food security. The Brahmaputra and Indus basins are most susceptible to reductions of flow, threatening the food security of an estimated 60 million people.

Regional water vapor convergence and divergence over the southern margin of the Qinghai-Xizang Plateau (QXP) can be regarded as a good factor for the formation of rainfall climate and extreme weather in the TP and its surroundings. In view of the key region in southern margin of the QXP (the key region for short), summer moisture transport and budget over the key region are analyzed based on the NCEP/NCAR reanalysis data from 1979 to 2010, combined with rainfall station data as well to explore its effects on the rainfall characteristics in the QXP and its surroundings. The main conclusions are summarized as follows. Influenced by the Indian low and the terrain of the QXP, three water vapor transport channels were transformed in the key region from the Bay of Bengal moisture flow, and those led to water vapor divergence over the key region where the southern boundary was the only input one. Meanwhile, different boundaries showed different monthly and interannual variations, especially for the contrary trend of the moisture budget intensity between the western and the eastern boundaries. The budget of input and output boundaries were affected by the activities of the Indian low and the South Asian monsoon, and the output boundaries moisture budget was directly connected with abnormal distribution of rainfall and the development of extreme drought and flood events in the QXP and even the monsoon region surroundings. In addition, the reliability of NCEP/NCAR and JRA-25 reanalysis data in qualitative research over the south margin of the QXP was confirmed by comparison of these tow datasets.

青藏高原南缘水汽输送和聚散过程决定着高原及其邻域的降水分布特征, 在提出"青藏高原南缘水汽输送关键区"(简称南缘关键区)概念的基础上, 利用NCEP/NCAR再分析资料分析了1979-2010年南缘关键区夏季水汽输送过程与收支变化, 并根据台站降水量观测资料探讨了南缘关键区各边界水汽收支与高原夏季降水分布的关系。结果表明, 孟加拉湾偏南风水汽流进入南缘关键区后, 在印度热低压与青藏高原大地形制约下, 形成了3条进入高原的水汽输送通道。这使得南缘关键区整体为多年平均水汽辐散区, 除南边界外, 其余均为水汽输出边界。南缘关键区各边界水汽收支年内与年际变化明显, 且东、西边界水汽输出强度变化特征相反。而各边界水汽收支与印度热低压和南海夏季风活动关系密切, 输出边界的水汽支出异常则直接影响着青藏高原乃至周边季风区的降水异常分布以及极端旱涝事件的发生、发展。此外, NCEP/NCAR与JRA-25再分析资料之间的对比验证表明, 这两种再分析资料在青藏高原南缘水汽输送过程的定性研究中是可靠的。

Based on the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Reanalysis (ERA-Interim hereafter) from 1979 to 2010, the average water vapor transport flux distribution in summer over the Qinghai-Xizang Plateau (QXP hereafter) is calculated and studied. Combined with the high resolution observational data of the daily precipitation over the QXP, four moisture paths influencing the precipitation over the QXP are found, which are defined as the paths of westerly, Arabian Sea, the northern side of Bay of Bengal and South China Sea, respectively. Moreover, the area and function of these paths influencing precipitation process over the QXP have been analyzed and addressed. The results show that the years of both strong (1979, 1984, 1996, 1998, 2002, 2004, 2007) and weak (1994, 2001, 2006) precipitation over the QXP are consistent with the results reflected from path of the northern side of Bay of Bengal. Compared with the rest paths, the influence of the westerly path is weakest, which only has an role in the northwest QXP from Shiquanhe to the south of Tarim Basin; The northern side of Bay of Bengal path has an effect in the central-southeastern QXP;the path of the South China Sea dominates the southeastern and central-south of QXP such as Naqu, Linzhi, Changdu, Yushu and other regions; Arabian Sea path has negative correlations with the rest three paths, especially with the northern side of Bay of Bengal path (<em>R</em>=-0.65, <em>P</em><0.05). Furthermore, Arabian Sea path indirectly modulates the central-southwestern QXP by adjusting the intensity of both the northern side of Bay of Bengal path and South China Sea path. These results suggest that both the water vapor transport path and pattern of precipitation over the QXP is coherently connected.

利用欧洲中期天气预报中心(ECMWF)提供的1979-2010年ERA-Interim再分析资料分析了青藏高原(下称高原)及附近夏季水汽输送通量分布情况,并结合基于迄今为止最全面的地面观测数据形成的高分辨率降水资料分析出4条影响夏季高原降水的水汽通道:西风带、阿拉伯海、孟加拉湾北部及南海通道。结果表明:高原夏季降水量高值年(1979、1984、1996、1998、2002、2004、2007年)、低值年(1994、2001、2006年)与孟加拉湾北部通道水汽输送强弱年有较好对应。夏季西风带通道的影响较弱,与其他3条低纬度通道的相关系数较小,是相对独立的水汽通道,主要影响高原西北部从狮泉河至塔里木盆地南侧地区;孟加拉湾北部通道影响高原中南偏东部地区;南海通道则对高原东南部以及中南部那曲、林芝、昌都、玉树等地区有影响;而阿拉伯海水汽通道与其他水汽通道都呈负相关关系,其中与孟加拉湾北部通道相关关系最显著,相关系数达到-0.65,该通道通过调节孟加拉湾北部通道和南海通道的向西水汽输送分量来影响高原中南偏西部地区的夏季降水。

In this study, the monthly precipitation data set at 113 stations during 1979-2014 over the Qinghai-Tibetan Plateau (QTP) provided by the National Meteorological Information Center, had been compared with 4 gridded precipitation data sets (APHRO, CMAP, GPCP, GPCC) and 8 reanalysis data sets (NCEP1, NCEP2, MERRA, ERA_Interim, ERA20c, 20CRv2, JRA55, CFSR).Compared with the observation, it was found that the AHPRO and GPCP can capture the spatial and temporal patterns of the summer precipitation over the QTP during 1979-2007 and 1979-2014, respectively.For the climatology of water vapor, the southern boundary is the main moisture source over the QTP in summer with the dominant channel in the lower layer.Meanwhile, both the western and northern boundaries are also the moisture input over the QTP, with the main channels in the middle layer and the lower layer, respectively.Furthermore, the water vapor output over the QTP is through the eastern boundary by means of its middle layer.Generally, QTP is a moisture sink in summer, and the moisture is convergent over it, to which moisture advection term makes the greatest contribution, while wind divergence term has a diverse effect.In addition, ERA_Interim and NCEP1 showed better ability to delineate these characteristic, however, MERRA was the worst.By comparing multiple datasets, it was shown that MERRA and ERA_Interim can better depict the water vapor transport condition over the local QTP and peripheral area, respectively.Exploring relationship between the precipitation variability over the southeastern QTP and the atmospheric circulation, we picked out the high and low value years according to precipitation index.By conducting the synthesis analysis on them, it was shown that the moisture from the western boundary was the most sensitive to climate change and the decrease of net income in dry years was greater than the increase of net income in wet years, and ERA_Interim and MERRA can represent the water vapor transport condition at different boundary and levels in dry years and wet years better, respectively.Conducting the synthesis analysis on the integrated water vapor transport, it was revealed that there is a zonally orientated anticyclone anomaly across the Indian subcontinent and the Bay of Bengal, and the strong westwards water vapor transport at its northern edge attributes to the excessive precipitation over the southeastern QTP.

利用国家气象信息中心提供的1979-2014年青藏高原（下称高原）地区（26°N-42°N，75°E-105°E）113个站点的逐月降水资料作为基准降水资料，与另外4套格点降水资料（APHRO、CMAP、GPCP、GPCC）和8套再分析的降水资料（NCEP1、NCEP2、MERRA、ERA_Interim、ERA20c、20CRv2、JRA55、CFSR）作对比，可得12套再分析资料中，APHRO能够最好地刻画出高原1979-2007年夏季降水的时空分布形态。GPCP次之，能够较好地刻画其1979-2014年的特征。就气候态而言，水汽主要由南边界输入高原，输入大值区是下层；另外水汽同样从西边界和北边界输入高原，主要的输入层分别是中层和下层；而水汽主要是从东边界中层输出。多套资料比较可知，ERA_Interim和MERRA分别能较好地刻画高原本地和其周围地区夏季水汽输送情况。研究高原东南部降水的年际变化和环流的关系，发现在印度半岛和孟加拉湾处有一异常的纬向反气旋，其北边缘加强的水汽输送导致了高原东南部降水的异常增多。

This paper studies the changing trend of annual and seasonal mean temperature, maximum temperature, minimum temperature, precipitation and sunshine duration etc. by using the observational data of 9 meteorological stations over the Nujiang River Basin in Tibet from 1971 to 2008. It also analyzes the variation trend of meteorological elements by climatic linear trend methods, and discusses the correlation between the linear trend of elements and latitude, altitude and longitude. The results show that the annual mean temperature has increased over the Nujiang River Basin with a rate of 0.26 oC/10a during the past 40 years, which is lower than that in Northeast China and Northwest China, and is higher than that in the Huaihe River basin and South China, and similar to that over the Qinghai-Xizang Plateau. The trends of mean maximum and minimum temperatures are increasing, the trend of diurnal temperature range is significantly decreasing at a rate of (-0. 13~-0.57) oC/10a. The annual precipitation increases significantly and the linear increasing rate is 21.0mm/10a, while that in all seasons increases. The annual sunshine duration decreases over the Nujiang River Basin with a rate of -31.7 h/10a, and the maximum decrease is in summer, and the rate of decrease is greater than that in the Huanghe River basin and eastern margin of the Qinghai-Xizang Plateau. In addition, the variation of maximum frozen soil depth shows a significant declining trend over the upper reaches of the Nujiang River Basin in Tibet, resulting from the increasing soil temperature, especially in Amdo. Correlation analysis demonstrates that sunshine duration is significantly negative with precipitation (all seasons) and surface vapor pressure (in summer and autumn). Results indicate that the principal causes for the decrease of sunshine duration are the significant increase of surface vapor pressure and precipitation in most parts of the Nujiang River Basin. The correlation between total cloud amount and diurnal temperature range is negative significantly, and is positive evidently with precipitation in summer, hence the relative humidity is not the main affecting factor with the decrease of total cloud amount. The amplification of annual temperature and precipitation became greater with the increase of altitude and latitude. The linear trend of sunshine duration is positively related with longitude, and the decreasing amplitude of sunshine duration in summer and winter decreases with increasing longitude.

Long time series of monthly air temperature and precipitation data, which were recorded at 16 meteorological observation stations in the Nujiang River basin and its adjacent areas, were employed to analyze spatial distributions and changes of these meteorological elements in this basin during the past decades. In this research, TFPW-MK (Trend-free Pre-whitening Mann-Kendall) test and BFAST (Breaks For Additive Seasonal and Trend) were used to determine trends in climate data and to detect abrupt changes within the trend and seasonal components, respectively. The results show that air temperature and precipitation increased southward along the Nujiang River and heavily negatively correlated with altitude. The regional difference in PCD was obvious and higher PCD values, more than 60%, were observed in the Nujiang River basin in Tibet Autonomous Region. Precipitation-concentration time (PCT) in the study area (except for Gongshan) mainly from late July to late August. Generally speaking, the Nujiang River basin has become warmer in the past decades. The annual mean air temperature increases at a rate of 0.36 ℃/10a.

利用怒江流域及其毗邻地区16 个气象台站长时序逐月气温和降水量数据,运用TFPW-MK (Trend-free Pre-whitening Mann-Kendall) 检验和重复迭代变化诊断等方法,分析了近几十年来怒江流域气候要素空间格局和变化特征。结果表明:(1) 怒江流域气温(年平均、年最高和年最低) 和年降水量由北向南总体呈递增,并与海拔相关性极为显著(α=0.01),且气候要素值随海拔升高而降低;(2) 降水集中度地域差异明显,西藏境内降水集中度多达60%以上,全流域降水集中期(除贡山站外) 多介于7 月下旬至8 月下旬;(3) 流域升温趋势显著,其年平均、年最高和年最低气温变化趋势多与纬度和海拔呈显著相关,其中年平均气温增幅为0.36 ℃10a;(4) 部分站点气温变化存在突变点,且其多出现于暖冬频发的20 世纪80 年代以后;(5) 年降水量总体有所增多,但变化趋势多不显著,无明显变点。

The Nujiang river is a typical area of lacking data with complicated terrain and climate characteristics. TRMM (Tropical Rainfall Measuring Mission) precipitation data can effectively describe the spatial distribution characteristics of regional precipitation, and it has great reference value to the area of lacking information. We use TRMM 3B42V7 data and 18 weather stations data to explore the spatial and temporal distribution characteristics of precipitation and analyze the accuracy of TRMM 3B42V7 data in the upper reaches of Nujiang river. The correlation coefficient method and spatial analysis method are used to solve the problem. By analyzing the correlation coefficient, it shows that the best correlation coefficient between TRMM 3B42V7 data and the site observation data occurs at monthly scale (<i>R</i>>0. 9), second is yearly scale (<i>R</i>>0. 5), the worst is daily scale (<i>R</i> < 0. 5). The two sets of data have strong correlation under monthly scale when it comes to areal precipitation (<i>R</i>≈0. 98). Time series also fit well though TRMM 3B42V7 data is slightly larger than the site observation data in the month of abundant precipitation. Spatial-temporal comparative analysis indicates that precipitation spatial distribution has good consistency of these two group data at different time scales though the local distribution characteristics are different. There is an underestimation tendency of TRMM 3B42V7 data in the northwest of the basin, and overestimation tendency in the southeast. Precipitation in most other area has little difference between TRMM 3B42V7 data and the site observation data. TRMM 3B42V7 data is also used to analyze the seasonal proportion of precipitation in the basin and it is found that seasonal patterns of precipitation in study area vary greatly. Precipitation in summer (from June to August) account for a large proportion of total annual precipitation. The ratio of precipitation in summer is 42%~72%, while the total ratios of spring (from March to May), autumn (from September to November) and winter (from December to February) to annual precipitation are 28%~58%.

利用1998-2013年热带测雨卫星TRMM 3B42V7降水数据产品和18个气象站点观测数据对怒江上游进行了降雨时空分布特征的对比分析，研究了TRMM 3B42V7数据产品在该区域的精度。结果显示：研究区内TRMM 3B42V7数据和站点数据相关性月尺度最强（R>0.9），年尺度次之（R>0.5），日尺度较差（R < 0.5）；流域面雨量两组数据在月尺度上有极强的相关性（R≈0.98），时间序列拟合较好，但在降水量大的月份TRMM 3B42V7数据较站点观测数据略偏大；不同时间尺度下两组数据的空间分布特征总体具有较好的一致性，局部分布特征有差异；流域西北和东南局部区域TRMM降水分别有低估和高估趋势，其他大部区域相当。利用TRMM 3B42V7数据对流域降水进行季节占比分析，结果显示，流域降水季节分配不均匀，夏季（6-8月）降水占全年降水总量的比例较大，高达42%~72%；其他春（3-5月）、秋（9-11月）、冬（12月至次年2月）三季节降水整体较少，总占比为28%~58%。

There is a cross place between the Himalayas with a west-east direction and Hengduan Mountains with a north-south directions in which the Yarlung Zangbo River,Nu River and Lang Chang River are moving through it on the southeast part of the Tibet Plateau.As there is a special topography conditions,both of the mountain blocking and moisture passage effects on the distribution of precipitation,climatic and natural zones are obvious.The mountain blocking effects resist the warm and humid stream to make the great difference of the precipitation,climatic and natural zones between the two sides of the mountains.Meanwhile,both of the mountain blocking and moisture passage effects form the special distribution of precipitation,climatic and natural zones in this region,which make a great natural contribution for mankind of forming an ideal heaven.

在我国藏东南地区,东西走向的喜马拉雅山脉与南北走向的横断山脉相交,雅鲁藏布江、怒江和澜沧江穿流于其间,这种特殊的地形条件具有的屏障和水汽通道综合作用对降水分布和气候自然带分布带来特殊的影响。屏障作用阻挡了西南季风的暖湿气流,带来山脉两侧(南北向或东西向)降水和气候自然带分布的巨大差异;同时,在该区,山地屏障作用与水汽通道作用同时存在,两者综合作用形成了特殊的降水和气候自然带分布,为形成人类的理想天堂-大香格里拉地区做出了自然贡献。