Summer Atmospheric Water Cycle under the Transition Influence of the Westerly and Summer Monsoon over the Yarlung Zangbo River Basin in the Southern Tibetan Plateau

This study compares the summer atmospheric water cycle,including moisture sources and consumption,in the upstream,midstream,and downstream regions of the Yarlung Zangbo River Basin in the southern Tibetan Plateau.The evolutions of moisture properties under the influence of the westerly and summer southerly monsoon are examined using 5-yr multi-source measurements and ERA5 reanalysis data.Note that moisture consumption in this study is associated with clouds,precipitation,and diabatic heating.Compared to the midstream and downstream regions,the upstream region has less moisture,clouds,and precipitation,where the moisture is brought by the westerly.In early August,the vertical wet advection over this region becomes enhanced and generates more high clouds and precipitation.The midstream region has moisture carried by the westerly in June and by the southerly monsoon from July to August.The higher vertical wet advection maximum here forms more high clouds,with a precipitation peak in early July.The downstream region is mainly affected by the southerly-driven wet advection.The rich moisture and strong vertical wet advection here produce the most clouds and precipitation among the three regions,with a precipitation peak in late June.The height of the maximum moisture condensation is different between the midstream region(325 hPa)and the other two regions(375 hPa),due to the higher upward motion maximum in the midstream region.The diabatic heating structures show that stratiform clouds dominate the upstream region,stratiform clouds and deep convection co-exist in the midstream region,and deep convection systems characterize the downstream region.

Climate change over the Yarlung Zangbo River Basin during 1961-2005

The Yarlung Zangbo River （YR） is the highest great river in the world, and its basin is one of the centers of human economic activity in Tibet. Using 10 meteorological stations over the YR basin in 1961-2005, the spatial and temporal characteristics of temperature and precipitation as well as potential evapotranspiration are analyzed. The results are as follows. （1） The annual and four seasonal mean air temperature shows statistically significant increasing trend, the tendency is more significant in winter and fall. The warming in Lhasa river basin is most significant. （2） The precipitation is decreasing from the 1960s to the 1980s and increasing since the 1980s. From 1961 to 2005, the annual and four seasonal mean precipitation is increasing but not statistically significant, especially in fall and spring. The increasing precipitation rates are more pronounced in Niyangqu and Palong Zangbo river basins, the closer to the upper YR is, the less precipitation increasing rate would be. （3） The annual and four seasonal mean potential evapotranspiration has decreased, especially after the 1980s, and most of it happens in winter and spring. The decreasing trend is most significant in the middle YR and Nianchu river basin. （4） Compared with the Mt. Qomolangma region, Tibetan Plateau, China and global average, the magnitudes of warming trend over the YR basin since the 1970s exceed those areas in the same period, and compared with the Tibetan Plateau, the magnitudes of precipitation increasing and potential evapotranspiration decreasing are larger, suggesting that the YR basin is one of the most sensitive areas to global warming.

Temporal and spatial variations of δ^18O in precipitation of the Yarlung Zangbo River Basin

This paper reveals the temporal and spatial variations of stable isotope in precipitation of the Yarlung Zangbo River Basin based on the variations of δ^18O in precipitation at four stations （Lhaze, Nugesha, Yangcun and Nuxia） in 2005. The results show that δ^18O of precipitation has distinct seasonal changes in the Yarlung Zangbo River Basin. The higher value of δ^18O occurs in spring prior to monsoon precipitation, and the lower value occurs during monsoon precipitation. From the spatial variations, with the altitude-effect and rainout process during moisture transport along the Yarlung Zangbo River Valley, δ^18O of precipitation is gradually depleted. Thus, δ^18O of precipitation decreases gradually from the downstream to the upstream, and the lapse rate of δ^18O in precipitation is approximately 0.34‰/100m and 0.7%J‰/100km for the two reasons. During monsoon precipitation, spatial variation of δ^18O in precipitation is dominated by the amount effect in the large scale synoptic condition.

A long-term record(1995-2019)of the dynamics of land desertification in the middle reaches of Yarlung Zangbo River basin derived from Landsat data

Widespread desertification in the middle part of the Yarlung Zangbo River(YZR)basin is threatening the sustain-able development of this region.To capture this process,a method was proposed for large-scale desertification monitoring by using Landsat images from 1995 to 2019.The method used an integrated classification method combined with a hierarchical decision tree and nearest neighbor classifiers.The spatio-temporal dynamics of the desertification pattern were analyzed to assist in the detection of possible driving forces.Using validation samples collected from Google Earth high-resolution images and field investigations,the overall accuracy of the classification in 2019 was 92.3%with a Kappa coefficient of 0.84.The major results were:(1)total sandy land area in 2019 was 734.1 km^(2),which accounted for 3.7%of the study area,prominently distributed along the wide river valleys and inlets of tributaries with a strip and discontinuous pattern.Sandy land tends to be distributed in the southern aspect regions with lower elevations and that are closer to rivers;(2)sandy land areas showed two temporal stages:a gradual increase of 102.4 km^(2)from 1995 to 2015 and a large decrease of 106.8 km^(2)from 2015 to 2019;(3)newly increased sandy land was distributed in the YZR Valley,while the revegetation on sandy land occurred mainly in the Lhasa River basin and some regions in the YZR Valley;and(4)increased sandy land area of 142.1 km^(2)was mainly distributed in the southern band of the two rivers.Correspondingly,revegetation on sandy land was more effective on the northern banks of the river valleys.These findings provide guidance for implementing vegetation recovery on sandy lands and provide important insights for maintaining sustainable development.

Hydrogeochemical and isotopic characteristics of spring water in the Yarlung Zangbo River Basin, Qinghai-Tibet Plateau, Southwest China

The Yarlung Zangbo River Basin(YZRB)is situated in the southern part of the Tibetan Plateau and remains in a mostly natural state.To understand the chemical characteristics of spring water and its controlling factors in the YZRB,68 sets of spring water samples were analyzed using hydrochemical and isotopic techniques.The spring water was found to be slightly alkaline with total dissolved solids(TDS)below 1000 mg L−1.Major ions were Mg2+,Ca2+,SO42−,and HCO3−.The spring water types in this basin were determined to be HCO3-Ca·Mg and SO4·Cl-Ca·Mg.Ion exchange and dissolution of carbonate,gypsum,and silicate were identified as the prevalent hydrogeochemical processes contributing and defining spring water chemistry in this basin.Saturation indices(SI)of most major minerals studied in this region were below zero,indicating that these minerals remain under-saturated in the spring water in this area.Overall,the rank of different processes in terms of their contribution to the chemical composition of spring water in the YZRB was carbonate weathering>evaporate dissolution>silicate weathering>precipitation input.The content of 18O in spring water ranged from−22.22‰to−14.08‰with a mean of−18.15‰.Samples collected below and close to the local and global meteoric water lines indicated that spring water in this area is derived from meteoric water with chemistry affected by evaporation.

Hydro-climatic Characteristics of Yarlung Zangbo River Basin since the Last Glacial Maximum

Global climate changes significantly impact the water condition of big rivers in glacierized high mountains. However,there is a lack of studies on hydrological changes within river basins caused by climate changes over a geological timescale due to the impossibility of direct observations. In this study, we examine the hydro-climatic variation of the Yarlung Zangbo River Basin in the Tibet Plateau since the Last Glacial Maximum(LGM) by combining δ18 O proxy records in Indian and Omani caves with the simulated Indian summer monsoon, surface temperature, precipitation, evapotranspiration and runoff via the Community Climate System Model and the reconstructed glacier coverage via the Parallel Ice Sheet Model. The mean river runoff was kept at a low level of 145 billion cubic meters per year until an abrupt increase at a rate of 8.7 million cubic meters per year in the B?lling-Aller?d interval(BA). The annual runoff reached a maximum of 250 billion cubic meters in the early Holocene and then reduced to the current value of 180 billion cubic meters at a rate of 6.4 million cubic meters per year. The low runoff in the LGM and Heinrich Stadial 1(HS1) is likely attributed to such a small contribution of precipitation to runoff and the large glacier cover. The percentage of precipitation to runoff was only 20%during the LGM and HS1. Comparison of glacier area among different periods indicates that the fastest deglaciation occurred during the late HS1, when nearly 60% of glacier area disappeared in the middle reach, 50% in the upper reach,and 30% in the lower reach. The rapid deglaciation and increasing runoff between the late HS1 and BA may have accelerated widespread ice-dam breaches and led to extreme outburst flood events. Combining local geological proxy records and regional simulations could be a useful approach for the study of paleo-hydrologic variations in big river basins.

Compound extreme events in Yarlung Zangbo River Basin from 1977 to 2018

Extreme climate events threaten human health,economic development,and ecosystems.Many studies have been conducted on extreme precipitation and temperature changes in the Yarlung Zangbo River Basin(YZRB).However,little attention has been paid to compound climate extremes.In this study,the variations of wet/warm compound extreme events in summer and dry/cold compound extreme events in winter over the past 42 years in the YZRB were investigated using eight extreme climate indices that were estimated using monthly temperature and precipitation observations.The results showed that the numbers of frost days and ice days tended to decrease on the spatiotemporal scale,while the maximum values of daily maximum temperature and daily minimum temperature exhibited increasing trends.The frequency of wet/warm compound extreme events was significantly higher from 1998 to 2018 than from 1977 to 1997.Dry/cold compound extreme events became less frequent from 1998 to 2018 than from 1977 to 1997.The rate of increase of wet/warm compound extreme events was about ten times the absolute rate of decrease of dry/cold compound extreme events.With regard to the spatial pattern,the frequency of wet/warm compound extreme events increased significantly in almost all parts of the YZRB,while that of dry/cold compound extreme events decreased across the basin.This study helps to improve our understanding of the changes in compound precipitation and temperature extremes in the YZRB from a multivariable perspective.

Integrating the ecosystem service in sustainable plateau spatial planning:A case study of the Yarlung Zangbo River Basin

The Yarlung Zangbo River Basin(YZRB)is a key ecological protection area on the Qinghai-Tibet Plateau(QTP).Determination of the ecosystem service values(ESVs)can help recognize the benefits of sustainable management.It is gradually becoming the main path that constructs plateau spatial planning of integrating ecological protection,and achieves global sustainable development goals(SDGs)in China.In this paper,the spatio-temporal dynamic evolutions of the ESVs were estimated on the multiple scales of“basin,subbasin and watershed”from 1980 to 2015.The main factors influencing ESVs were explored in terms of physical geography,human activities,and climate change.It had been proposed that sustainable spatial planning including ecological protection,basin management,and regional development was urgent to set up.Our results show that the increase in wetland and forest and results in an increase of 9.4%in the ESVs.Attention should be paid to the reduction of water and grassland.Water conservation(WC),waste treatment(WT),and soil formation and conservation(SFC)are the most important ecosystem services in the YZRB.At present,the primary problem is to solve the ESVs decreasing caused by glacier melting,grassland degradation,and desertification in the upper reaches region.The middle reaches should raise the level of supply services.Regulation services should be increased in the lower reaches region on the premise of protecting vegetation.The ESVs in adjacent watersheds are interrelated and the phenomenon of“high agglomeration and low agglomeration”is obvious,existing hot-spots and cold-spots of ESVs.Additionally,when the altitude is 4500-5500 m,the temperature is 3-8°C,and the annual precipitation is 350-650 mm,ESVs could reach its maximum.A framework of sustainable plateau spatial planning could provide references to delimit the ecological protection red line,key ecological function zone,and natural resource asset accounting on the QTP.

PRESENT STATUS AND CAUSE OF LAND DESERTIFICATION IN THE YARLUNG ZANGBO RIVER BASIN

The Yarlung Zangbo River basin is a spacial zone in the south of Xizang, the types, distribution and causes of desertified lands have special features. The type, area, distribution and damage of desertification land in the Yarlung Zangbo River basin are firstly analysed in detail by using latest investigation information. According to the classification criteria of desertified land types and grades, the desertified land in the Yarlung Zangbo River basin can be divided into three grades and five types: fixed sand (dune) land, semi bare sand and gravel land, semi fixed sand (dune) land, base sand and gravel land, and shifting sand (dune) land. The desertified lands in the basin are mainly distributed in the wide valley floor and tributary junction area. The main factors affecting desertification are fragile eco environment, climate warming and drying and over exploitation of land resources. The man made factors leading to desertification in the Yarlung Zangbo River basin are over cutting and over grazing, dominated by over grazing.

藏东南雅江流域冰-岩崩灾害链研究进展

全球气候变暖导致冰-岩崩及其灾害链成为研究热点,然而由于此类灾害多发于高寒地区,监测和模拟手段不足,研究困难且成果有限。我国西藏东南部雅鲁藏布江流域是冰-岩崩灾害高发区,也是水电建设重要区域,其冰/岩体稳定性对水利工程建设、运营及人民安全构成严重威胁。在全面梳理国内外研究现状的基础上,汇编了雅江流域近70年来有相关记载的冰-岩崩事件;通过深入调查分析,对冰-岩崩灾害进行了重新界定,并探究了该地区冰-岩崩灾害的时空分布规律;进一步,结合雅江流域独特的地理特征,初步揭示了冰-岩崩的形成机制,并将冰-岩崩灾害划分为冰-岩崩泥石流灾害、冰-岩崩堵江溃坝型灾害、冰-岩崩冰湖溃决型灾害和冰-岩崩库坝失效型灾害四种。在此基础上,基于CiteSpace可视化分析软件和WoS核心合集数据库,定量分析了最近25年(1999—2023年)国内外对于冰-岩崩灾害的研究现状,指出了不同时间段的研究热点和发展趋势。上述成果为雅江流域冰-岩崩灾害的深入研究及重大水利工程防灾减灾提供参考价植。

基于RUSLE模型的雅鲁藏布江流域土壤侵蚀评价

[目的]研究雅鲁藏布江流域土壤侵蚀时空变化特征,并分析气候和植被覆盖变化对土壤侵蚀的影响,以期为高寒区土壤侵蚀防治、生态系统保护和水土资源开发利用提供理论支撑。[方法]以雅鲁藏布江流域为研究区,采用RUSLE模型定量评估了1980—2017年流域土壤侵蚀的时空变化特征。[结果]1980—2017年,雅江流域土壤侵蚀强度整体呈现先减小后增加的趋势,1980—1999年年均土壤侵蚀模数波动下降,2000—2017年年均土壤侵蚀模数则呈现不显著上升趋势;流域中上游地区土壤侵蚀变化较为显著,下游地区侵蚀强度先增加后减小。年均土壤侵蚀模数与降雨侵蚀力呈显著正相关关系,Pearson相关系数为0.92,而与NDVI关系不显著。不同土地利用类型中,土壤侵蚀最强烈的是未利用地,其次是稀疏草地,由于其面积占比最高,对流域总侵蚀量的贡献比超过54%。[结论]降雨是影响雅江流域土壤侵蚀强度变化的主要因素,未来土壤侵蚀防治的重点区域应为流域东部下游降雨量较大的地区,重点防范极端降雨造成的水土流失。

多源潜在蒸散发产品在雅鲁藏布江流域的适用性评估与融合

基于2001—2018年监测站点观测的蒸发皿数据,分别在站点尺度和流域尺度上对GLEAM、MOD16A2、GLDAS_Noah和ERA5共4种遥感潜在蒸散发产品进行评估,选出适应性较好的3种遥感产品,运用Triple Collocation方法进行融合,并分析其时空变化特征。结果表明:在站点尺度上,ERA5遥感产品相关性较为显著(相关系数CC=0.72),精确度最高(相对偏差Bias=-22.48%,均方根误差RMSE=39.24 mm/月),更适用于雅鲁藏布江流域,MOD16A2和GLDAS_Noah次之;MOD16A2、GLDAS_Noah和ERA5分别占融合数据PET_(TC)的31.12%、30.64%和38.24%,对比PET_(TC)与3种遥感产品,PET_(TC)融合数据在流域内精度有所提高;融合数据PET_(TC)的潜在蒸散发峰值出现在2009年,雅鲁藏布江流域多年平均潜在蒸散发呈现从中部向上、下游逐渐减小的趋势,在流域东南角出现潜在蒸散发量最大值。在雅鲁藏布江流域内获得更精准的潜在蒸散发并揭示其变化规律,可为研究流域水资源的供需平衡和生态系统的稳定性提供数据支撑。

基于深度学习的改进ERRIS径流预报实时校正模型

为提高径流预报精度,基于长短期记忆网络(LSTM)改进ERRIS模型,构建了径流预报实时校正的ERRIS-LSTM模型,以雅鲁藏布江流域和椒江流域为例进行对比分析。结果表明:与ERRIS模型相比,ERRIS-LSTM模型使雅鲁藏布江流域和椒江流域径流预报的纳什效率系数分别提升了4.1%和1.1%,均方根误差分别减小了67.7%和5.7%,使雅鲁藏布江流域中、低水流量的百分比偏差分别降低了75.5%和79.1%,椒江流域低水流量统计指标均改善超过20%;ERRIS-LSTM模型能够充分获取误差序列的序贯相关性,生成的集合预报比ERRIS模型预报的整体精度更高,连续排序概率评分降低了75%以上,不确定性更小,可靠性更强;相比于LSTM模型的校正结果,ERRIS-LSTM模型可以额外提供校正结果的不确定性信息,在业务预报和防洪决策中具有重要的应用前景。

雅鲁藏布江流域奴下水文站极端降水与极端径流的关系研究

青藏高原是亚洲十多条大江大河的发源地,被称为“亚洲水塔”。随着全球变暖加剧,青藏高原极端水文和气象事件频发。然而,其复杂的气候和下垫面(冰川、积雪、和冻土等)特征,限制了对该地区极端径流对极端降水响应关系的理解。本文以青藏高原南部的雅鲁藏布江流域为例,利用逐日降水和径流数据,通过改进极端径流阈值法,并结合相关分析等方法,研究了不同发生概率下极端径流与极端降水之间的关系。研究结果表明:(1)雅鲁藏布江流域的极端径流事件通常持续1~2天,且随着发生概率的减小,事件持续时间相应缩短。(2)发生概率为10%、5%和1%的极端径流与极端降水的相关系数在0.07~0.28之间(P<0.01),且随着极端降水发生概率的增加,两者之间的响应关系逐渐加强。(3)在奴下水文站,极端径流对该水文站以上雅鲁藏布江流域极端降水的响应强度最大,而对奴下气象站和林芝气象站的响应相对较弱,同时,最高响应时间滞后一天。此外,极端径流对极端降水的响应关系也受到流域湿润程度、植被状况和土壤湿度等因素影响。本文改进的极端径流识别方法能够有效捕捉雅鲁藏布江流域受极端降水影响的极端径流事件,提高了径流组分复杂的高寒流域极端径流对极端降水响应关系的理解。与此同时,该研究还能够为气候变暖背景下雅鲁藏布江流域的水资源管理和区域经济发展提供重要的理论支撑和科学指导。

西藏特有种砂生槐的研究现状和展望

砂生槐为西藏“一江两河”地区特有的小灌木,因其作为固沙、薪柴、药用、蜜源、饲用等植物,备受人们的关注。本文从植物形态学、遗传学和细胞学、生长发育、生态适应性、以及饲用和药用价值等综述了砂生槐的相关研究成果,并对其种群的复壮、资源的驯化选育、苦参碱开发、蛋白饲料应用等研究方向进行了展望,以期为砂生槐进一步开发和应用,提供重要参考。

1961-2010年西藏雅鲁藏布江流域降水量变化特征及其对径流的影响分析

采用1961-2010年雅鲁藏布江流域6个气象站近50a降水量的实测数据，统计降水量的年、干季、湿季平均序列；结合流域6个水文站近50a年径流序列资料，分析雅鲁藏布江流域降水变化特征及其对径流量的影响．研究表明：雅鲁藏布江流域1961-2010年近50a年平均降水量表现为不显著增加，增加速率为3．3mm·（10a）一，其中干季、湿季分别为1．9mm·（10a）^-1和1．4mm·（10a）^-1，均为增加趋势；降水量的年代际变化在20世纪60年代相对偏多，70年代较平稳，而80年代为最少，到90年代有所回升，21世纪前10a降水量处于不显著的增多态势．雅鲁藏布江径流的变差系数C，值在0．15～0．40之间，年际变化较小．径流的年代际变化总体上存在一定的周期性波动，20世纪60年代是一个相对的丰水期，70年代减少，80年代达到最小值，之后径流有所回升，进入21世纪前10a呈不显著增加趋势．年、湿季尺度上径流量和降水量的相关显著，湿季作为径流主要形成期，其降水量的多寡直接影响流域径流量的丰枯，湿季降水量的增减影响着流域径流量的增减．由此可见，降水变化是雅鲁藏布江天然径流最主要影响因子，最终也决定了雅鲁藏布江流域年径流量的丰枯．

近45年雅鲁藏布江流域极端气候事件趋势分析

利用雅鲁藏布江流域10个气象台站1961-2005年逐日最高气温、最低气温和日降水量资料,分析了该流域气温和降水等气候极端事件的变化趋势。研究表明:近45年以来,雅鲁藏布江流域夜间和白天极端低温日数分别以1.94和0.97天/10年的趋势在显著减少,夜间极端低温日数减少在冬季最明显,白天极端低温日数在秋季减少最明显;夜间极端高温日数和白天极端高温日数分别以3.03和1.26天/10年的速度显著增加,夜间极端高温日数增加在夏季最明显,白天极端高温日数增加在冬季最明显;日较差以0.11oC/10a的速度在显著减少,主要发生在冬季;最大的1天降水总量和逐年连续无降水天数有减少趋势,最大的5天降水总量、中雨天数、逐年平均降水强度和逐年连续降水天数有增加趋势,90年代以来增加趋势明显,与该地区经向风与水汽通量增加有关。

藏南罗布莎蛇绿岩壳层熔岩地球化学特征及成因

罗布莎蛇绿岩是雅鲁藏布江蛇绿岩带东段出露较好,也是研究程度较高的蛇绿岩片之一,对其壳层熔岩研究表明,该熔岩属于亚碱性玄武岩与安山岩/玄武岩之间的过渡类型,富集Rb、K、Ba等大离子亲石元素,高场强元素具有轻微左倾正斜率分布特征,并亏损Nb、Ta,反映出该蛇绿岩受到了俯冲作用的影响,稀土元素显示LREE亏损、HREE平缓的球粒陨石标准化分布模式,体现了该蛇绿岩N-MORB的地球化学特征,结合第一过渡系元素地球化学特征,通过对其构造环境的判别,提出罗布莎蛇绿岩属于岛弧型蛇绿岩范畴,其构造环境应为俯冲带之上(SSZ)的弧间盆地。

雅鲁藏布江流域降水中δ^(18)O的时空变化

通过研究2005年西藏雅鲁藏布江流域拉孜、奴各沙、羊村和奴下4个站点降水中的δ18O变化,揭示了雅鲁藏布江流域降水中稳定同位素的时空变化规律。研究显示,雅鲁藏布江流域降水中δ18O季节变化明显,高值出现在季风降水之前的春季,而低值出现在季风降水季节,其间降水中δ18O具有明显的“降水量效应”;从空间上看,降水中的δ18O从下游至上游递减,造成这种分布特征主要是由于“高程效应”以及水汽远距离输送导致其中的18O被贫化的结果。经计算表明,雅鲁藏布江流域降水中δ18O由于“高程效应”造成的递减率为0.34‰/100m,而水平方向上自东向西由于水汽远距离输送造成的递减率为0.7‰/100km。从季风期间大范围的降水过程来看,降水中δ18O的空间变化主要受“降水量效应”制约。

雅鲁藏布江流域土地沙漠化现状与成因初步研究——兼论人为因素在沙漠化中的作用

利用最新的普查数据，首次详尽分析了该区土地沙漠化的类型、面积、分布及危害，通过对其沙漠化影响因素及其相互关系的分析，辅以定量方法系统阐述了该区土地沙漠化的成因，并探讨了藏南河谷农牧区人为因素在沙漠化过程中的作用及其机理。