Spatio-temporal evolution and topographic gradient effect of land use and ecosystem service value in the Lhasa River Basin

The Lhasa River Basin forms an essential human settlement area in the southern part of the Qinghai-Tibet Plateau.This study employed ecosystem service value(ESV)evaluation model,terrain gradient grading,and Geodetector to analyze land use and ESV in the Lhasa River Basin from 1985 to 2020.The findings reveal that:(1)From 1985 to 2020,grassland was the dominant land use.There was a trend of grassland reduction and the expansion of other land types.(2)ESV has increased over the research period(with a total increase of 0.84%),with higher values in the southeast and lower values in the northwest.Grassland contributed the most to ESV,and climate regulation and hydrological regulation were the ecosystem services that contribute the most to ESV.(3)Natural factors like NDVI and altitude,as well as economic factors like population density and distance from roads,influenced the spatial differentiation of ESV,the explanatory power of NDVI reached up to 0.47.The interaction between factors had a greater impact than individual factors.These research results can provide theoretical support for national spatial planning and ecological environment protection in the Lhasa River Basin and other similar areas.

Alpine wetlands in the Lhasa River Basin, China

The Lhasa River Basin is one of the typical distribution regions of alpine wetlands on the Tibetan Plateau. It is very important to get a better understanding of the background and characteristics of alpine wetland for monitoring, protection and utilization. Wetland construction and distribution in the basin were analyzed based on multi-source data including field investigation data, CBERS remote sensing data and other thematic data provided by 3S technology. The results are （1） the total area of wetlands is 209,322.26 hm^2, accounting for 6.37% of the total land area of the basin. The wetlands are mainly dominated by natural wetland, with artificial wetland occupying only 1.09% of the wetland area; marsh wetland is the principal part of natural wetland, dominated by Kobresia littledalei swampy meadow which is distributed in the river source area and upstream of Chali, Damshung and Medro Gongkar counties. The ratio and type of wetlands in different counties differ significantly, which are widely distributed in Chali and Damshung counties （accounting for 62% of the total wetland area）. （2） The concentrated vertical distribution of wetlands is at an elevation of 3600-5100 m The wetlands are widely distributed throughout the Yarlung Zangbo River Valley from river source to river mouth into the Yarlung Zangbo River. Marsh wetland is dominant in the source area and upstream of the river, with the mosaic distribution of lakes, Kobresia litUedalei and Carex moorcroftii swampy meadow, shrubby swamp and river; as for the middle-down streams, the primary types are river wetland and flooded wetland. The distribution is in a mosaic pattern of river, Kobresia humilis and Carex moorcroftii swampy meadow, Phragmites australis and subordinate grass marsh, flooded wetland and artificial wetland.

The trend on runoff variations in the Lhasa River Basin

Taking the Lhasa River Basin above Lhasa hydrological station in Tibetan Plateau as a study area, the characteristics of the annual and monthly mean runoff during 1956-2003 were analyzed, based on the hydro-data of the two hydrological stations （Lhasa and Tanggya） and the meteorological data of the three meteorological stations （Damxung, Lhasa and Tanggya）. The trends and the change points of runoff and climate from 1956 to 2003 were detected using the nonparametric Mann-Kendall test and Pettitt-Mann-Whitney change-point statistics. The correlations between runoff and climate change were analyzed using multiple linear regression. The major results could be summarized as follows： （1） The annual mean runoff during the last 50 years is characterized by a great fluctuation and a positive trend with two change points （around 1970 and the early 1980s）, after which the runoff tended to increase and was increasing intensively in the last 20 years. Besides, the monthly mean runoff with a positive trend is centralized in winter half-year （November to April） and some other months （May, July and September）. （2） The trends of the climate change in the study area are generally consistent with the trend of the runoff, but the leading climate factors which aroused the runoff variation are distinct. Precipitation is the dominant factor influencing the annual and monthly mean runoff in summer half year, while temperature is the primary factor in winter season.

Distribution and land use characteristics of alluvial fans in the Lhasa River Basin,Tibet

In Lhasa River Basin(LRB),land suitable for settlement or living is experiencing a shortage of resources.Alluvial fans have the potential to alleviate this problem.However,basic information,such as the distribution and land use types of alluvial fans,is rarely studied.In this study,Google Earth,ArcGIS and visual interpretation were used to obtain the outlines,areas,quantities and distribution of alluvial fans.Meanwhile,to show the utilisation potential of alluvial fans,we analysed the land use,their distance from the roads,places(town and village)and rivers.The results showed 826 alluvial fans exist in LRB,with a total area of 1166.03 km2.The number of alluvial fans with areas between 0.1 and 1 km2 is 517,accounting for 62.59%of the total number of alluvial fans.Grassland is the dominant land use type,accounting for 68.70%of the total area of alluvial fans.The cropland area accounted for 2.16%of alluvial fans and accounted for 18.98%of the total cropland area in LRB.Exactly 93.70%,53.63%and 61.86%of the total number of alluvial fans were located within 5 km from the tertiary road,village,and river,respectively.To sum up,our survey results showed that alluvial fans are important land resources in LRB and may have huge utilisation potential.

Machine learning-based identification for the main influencing factors of alluvial fan development in the Lhasa River Basin,Qinghai-Tibet Plateau

Alluvial fans are an important land resource in the Qinghai-Tibet Plateau with the expansion of human activities. However, the factors of alluvial fan development are poorly understood. According to our previous investigation and research, approximately 826 alluvial fans exist in the Lhasa River Basin(LRB). The main purpose of this work is to identify the main influencing factors by using machine learning. A development index(Di) of alluvial fan was created by combining its area, perimeter, height and gradient. The 72% of data, including Di, 11 types of environmental parameters of the matching catchment of alluvial fan and 10 commonly used machine learning algorithms were used to train and build models.The 18% of data were used to validate models. The remaining 10% of data were used to test the model accuracy. The feature importance of the model was used to illustrate the significance of the 11 types of environmental parameters to Di. The primary modelling results showed that the accuracy of the ensemble models, including Gradient Boost Decision Tree,Random Forest and XGBoost, are not less than 0.5(R^(2)). The accuracy of the Gradient Boost Decision Tree and XGBoost improved after grid research, and their R^(2) values are 0.782 and 0.870, respectively. The XGBoost was selected as the final model due to its optimal accuracy and generalisation ability at the sites closest to the LRB. Morphology parameters are the main factors in alluvial fan development, with a cumulative value of relative feature importance of 74.60% in XGBoost. The final model will have better accuracy and generalisation ability after adding training samples in other regions.

Determining Critical Support Discharge of a Riverhead and River Network Analysis： Case Studies of Lhasa River and Nyangqu River

A riverhead is the demarcation point of continuous water channel and seasonal channel, which is characterized by a criti- cal flow that can support a continuous water body. In this study, the critical support discharge （CSD） is defined as the critical steady flows required to form the origin of a stream. The CSD is used as the criterion to determine the beginning of the riverhead, which can be controlled by hydro-climate factors （e.g., annual precipitation, annual evaporation, or minimum stream flow in arid season）. The CSD has a close correlation with the critical support/source area （CSA） that largely affects the density of the river network and the division of sub-watersheds. In general, river density may vary with regional meteorological and hydrological conditions that have to be considered in the analysis. In this paper, a new model referring to the relationship of CSA and CSD is proposed, which is based on the physical mechanism for the origin of riverheads. The feasibility of the model was verified using two watersheds （Duilongqu Basin of the Lhasa River and Beishuiqu Basin of the Nyangqu River） in Tibet Autonomous Region to calculate the CSA and extract river networks. A series of CSAs based on different CSDs in derived equation were tested by comparing the extracted river networks with the reference network obtained from a digitized map of river network at large scales. Comparison results of river networks derived from digital elevation model with real ones indicate that the CSD （equal to criterion of flow quantity （Qc）） are 0.0028 m3/s in Duilongqu and 0.0085 m3/s in Beishuiqu. Results show that the Qc can vary with hydro-climate conditions. The Qc is high in humid region and low in arid region, and the optimal Qo of 0.0085 m3/s in Beishuiqu Basin （humid region） is higher than 0.0028 m3/s in Duilongqu Basin （semi-arid region）. The suggested method provides a new application approach that can be used to determine the Qo of a riverhead in complex geographical regions, which can also reflect the effect of hydro-climate change on rivers supply in different regions.

基于VIC_glacier模型的拉萨河水文模拟及冰川径流研究

拉萨河作为青藏高原南部雅鲁藏布江最大的支流,冰川融水是其径流的重要组成部分。本文基于VIC模型和度日模型构建的VIC_glacier模型,模拟了1990—2010年拉萨河流域径流过程。结果表明:(1)与VIC模型相比,VIC_glacier模型在研究区的径流模拟效果更好,日径流模拟值与观测值的相关系数接近0.8,纳什效率系数在0.75以上;(2)从上游到下游,冰川融水对径流的贡献率分别为21.4%(旁多站)、17.7%(唐加站)、14.5%(拉萨站),呈逐渐减少趋势;(3)冰川径流和非冰川径流年内变化均呈现“单峰型”形态,且在8月份达到峰值;(4)1990—2010年间,年冰川径流量整体呈现上升趋势,与同期气温上升的变化规律一致;年冰川融水对径流的贡献率与年降水量呈反比关系。研究成果可为拉萨河流域的水资源管理提供参考。

拉萨河流域土地利用与生态系统服务价值时空演变及驱动因素

土地利用变化对生态文明建设产生强烈影响,进而威胁经济社会与生态环境的可持续发展。基于高精度土地利用数据,分析了拉萨河流域2000—2020年土地利用和生态系统服务价值(Ecosystem Service Value,ESV)时空演变特征,并借助PLUS模型和地理探测器分别探索了土地利用变化和ESV空间分异的驱动因素。结果表明:(1)2000—2020年拉萨河流域土地利用以草地为主,占流域总面积的85.23%。土地利用呈草地缩减,其余地类扩张的趋势。其中,草地减少2.45%,建设用地、水域和林地分别扩张199.72%、44.64%和21.97%。(2)流域土地利用变化受海拔、年均地温、距湖泊和水库距离等因素影响,其中,海拔对耕地、林地、水域和建设用地扩张的贡献度分别高达0.18、0.11、0.28和0.13,坡度和年均地温对草地和未利用地变化的贡献度分别为0.14和0.15。(3)2000—2020年流域ESV总体增加1.14%(14.96×108元),草地和气候调节分别为ESV贡献最突出的土地利用类型和生态系统服务类型,两者的贡献率分别为87.13%和25.50%。(4)流域ESV具有显著空间分异性,受NDVI、海拔、年均风速和年均气温等因子影响。其中,NDVI的解释力高达0.46,任意两两因子的交互均会增强ESV的分异性。研究结果可为拉萨河流域及类似区域国土空间规划和生态文明建设提供科学参考。

考虑生态流量的梯级水库主从博弈优化调度研究

针对传统集中式多目标优化范式未充分考虑多利益相关主体博弈关系对水库调度决策的影响,导致难以保障河道生态流量的现实问题,设置了共同保障和单独保障两种生态流量保障情景,构建了发电服从防洪调度原则下的梯级水库主从博弈优化调度模型,并在拉萨河流域旁多直孔梯级水库开展了实例研究。结果表明:梯级水库在共同保障生态流量下综合效益最优,仅由直孔水库单独保障生态流量造成调度效益难以凸显,其中防洪效益降低4.35%,整体发电效益降低1.66%;效益降低的主要原因在于单库保障模式下枯水期旁多水库倾向于蓄水而减少下泄,导致直孔水库过度下降水位来保障生态流量。

拉萨河流域梯级电站水光互补调度对水文情势的影响分析

梯级电站水光互补调度能提高光伏消纳能力和系统总发电量,但也要求调整梯级电站的调度规则,进而会加剧梯级电站下游的水文情势改变。为定量评价水光互补调度对水文情势的影响,以系统总发电量和总保证出力最大为目标,构建了拉萨河流域梯级电站水光互补优化调度模型,提出了基于水光互补的梯级电站优化调度方案,分析评价了不同优化调度方案的水文情势改变度。结果表明:梯级电站的水光互补优化调度能有效提升电力系统的总发电量和总保证出力;水光互补后拉萨河水文情势的综合改变度略大于水光互补之前,处于轻度至中度改变的临界值附近。研究成果可为拉萨河的水光互补调度及流域综合管理提供科学方法和依据。

拉萨河中下游流域典型湿地植物群落的数量分类与排序

为了更好的保护和修复拉萨河流域湿地生态系统,提升湿地的生态和社会价值。以拉萨河中下游流域5种典型湿地的植被群落为研究对象,共布置100个样方。运用群落类型划分方法、CCA排序和NMDS分析方法,探讨拉萨河中下流域5种典型湿地的植物群落数量分类及分布与环境梯度间的关系。结果表明:(1)拉萨河中下流域5种典型湿地的植物群落可划分为3种类型,即高山嵩草、蕨麻委陵菜草本群落为研究区的主要群落,沿线植被分布与环境梯度间的关系显著。(2)CCA二维排序图、NMDS分析将样地分为3个生态类型,间接验证了SPSS群落类型划分的结果。(3)研究区内地形复杂,小气候作用显著,考虑到环境因子数据的CCA排序效果好于仅采用植物样方数据的SPSS群落类型划分。因此,将CCA二维排序与SPSS聚类分析结合使用,能很好反映物种与环境因子间的生态关系。

拉萨河流域湿地植物群落多样性对草地生态系统功能的影响

湿地植物群落多样性能够反映湿地生态系统的健康状况和生态功能。因此,研究湿地植物群落多样性对草地生态系统功能的影响,对于保护湿地植物资源、促进草地生态系统健康发展具有重要意义。本文通过对拉萨河流域湿地植物群落多样性进行剖析,分析不同植物群落结构对草地生态系统功能的影响,提出维护湿地植物群落多样性的措施,为保护拉萨河流域湿地植物资源、促进草地生态系统的健康发展提供科学依据。

拉萨河水体砷和镉的分布特征与健康风险评价

为了解拉萨河流域水体中化学致癌物As和Cd的空间分布特征和健康风险水平,对拉萨河中下游和堆龙曲支流16个采样点进行水样采集,测量As和Cd浓度,并采用健康风险评价模型对As和Cd经饮水途径引起的致癌风险进行评价。结果表明,拉萨河水体As和Cd平均质量浓度分别为(2.280±0.969)和(0.092±0.017)μg·L^(-1),未超过GB 5749—2022《生活饮用水卫生标准》规定限值,达到GB 3838—2002《地表水环境质量标准》中I类和Ⅱ类水质标准。拉萨河中下游和堆龙曲支流水体As浓度均呈沿程增长趋势;而Cd浓度在中下游水体呈沿程下降,在堆龙曲支流呈沿程增长趋势。在地理分布上,As浓度随纬度增加而下降,随经度增加而上升;Cd浓度随纬度增加而上升,随经度增加而下降。健康风险评价结果表明,与Cd相比,As为拉萨河流域水体起主导作用的化学致癌物,贡献了超过98%的致癌风险。拉萨河流域水体As和Cd经饮水途径导致的致癌风险总体处于可接受的安全水平。相比于少年和成年,幼儿为更敏感的健康风险受体,受到As和Cd的危害相对更大,需要在幼儿饮水安全方面给予更多关注。

拉萨河流域水沙过程模拟及对植被覆盖和气候变化的响应

针对青藏高原日趋严重的水土流失现象,以位于青藏高原中南部的拉萨河流域为研究区域,通过搭建流域月尺度SWAT模型,探究植被覆盖和气候变化对流域水沙演变的影响。主要结论如下:(1)SWAT模型适用于拉萨河流域水沙模拟。(2)1991-2010年植被覆盖整体上呈退化趋势,植被覆盖变化对年径流变化的影响较弱,而流域输沙量对植被覆盖变化的敏感程度较显著,尤其在极端恶劣植被覆盖情景下,流域年均输沙量增加约70.15%。(3)气温升高2℃时,降水变化率每增加10%,年径流和年输沙量变化率则分别增加16.01%和28.70%。不同气候变化情景下,输沙量和径流的变化趋势并非总是完全一致。

未来气候变化下拉萨河流域径流变化趋势研究

【目的】气候变化引起水文循环的变化,主要表现为降水、径流等的显著改变。【方法】基于拉萨河流域分布式径流模型,应用第六次国际耦合模式比较计划(CMIP6)的4个气候模式数据,分析未来气候变化情景下拉萨河的径流变化。【结果】结果显示:SSP1-2.6情景模式下,拉萨河上中下游年径流深均呈减少趋势,约减少42%,但月径流量年内分配比例较实测月径流分配比例变化不大;SSP2-4.5情景模式下,总体上呈增加趋势,约增加1.5%,中上游径流深呈减少趋势,约减少1%~7%,下游支流呈增加趋势,约增加1%~37%;SSP5-8.5情景模式下,总体上呈增加趋势,约增加10%,下游支流增加趋势更加显著,约增加17%。【结论】结果表明:在CMIP6未来气候情景模式下,径流变化较为显著且不同情景模式差异较大;未来径流深变化趋势与未来降水变化趋势较为一致;拉萨河流域未来不同气候情景模式下径流深时空分布存在差异。通过对CMIP6未来气候模式进行模拟,分析拉萨河流域径流变化特征,为区域水文水资源配置、水资源利用等提供参考依据。

基于生态廊道识别的拉萨河流域生态安全格局构建

构建生态安全格局对于保障区域生态安全、优化国土生态空间具有重要意义。以拉萨河流域为研究区,基于“生态源地-阻力面-生态廊道”的区域生态安全格局构建范式,评估流域土壤保持、水源涵养、固碳、生境质量四项生态系统服务,基于生态系统服务重要性分级识别生态源地;选择土地覆被类型、归一化植被指数、地形起伏度、坡度、距道路距离、距水体距离作为主要阻力因子,利用熵权法形成综合阻力面;利用Linkage Mapper工具基于最小成本路径理论识别生态廊道并判定生态节点,构建流域生态安全格局。结果表明:提取生态源地20个,总面积2531.42 km^(2),占研究区总面积的7.77%;生态廊道36条,总长度916.87 km,与拉萨河干流平行呈“二”字型分布;生态节点13个,集中分布在裸地、裸岩、低覆盖度草地等地类,构建以生态源地-生态廊道-生态节点组成的“面-线-点”结构生态网络。研究结果为拉萨河流域生态安全和生态经济协调提供数据支持,为区域生态保护与可持续发展提供科学参考。

拉萨河流域河岸带湿地土壤CO_(2)排放对变温的响应

通过对26份青藏高原拉萨河流域湿地土壤样品的分析,发现土壤有机碳和总氮呈现中游西部流域低东部流域高,汇入雅鲁藏布江口较低,源头彭措较高;土壤中CO_(2)排放速率随着培养温度的升高而增加,下游各位点CO_(2)平均排放速率显著高于中游和上游.土壤呼吸温度敏感性(Q_(10))在流域内汇入口和下游左侧流域(堆龙曲)表现与排放速率相似的特征,更好地突出了在下游右侧流域(墨竹工卡流域)和上游流域(麦地藏布流域)的土壤温度敏感性较低的特征.通过地理探测器探寻气象、植被、地理、双评价、生化、人口经济6个圈层对Q_(10)值的不同影响,结果表明:气象(降雨、太阳辐射)、地理(流域、海拔)、生化、人口经济等因素对Q_(10)有较强影响,其中降雨(80.76%)和太阳辐射(74.68%)在气候因素中占主要影响;流域(88.95%)分布的q值在地理因素中起到重要作用;生化因子中,各检测指标对Q_(10)的影响排序为OC(88.16%)>MBC/OC(78.72%)>MBN/TN(77.30%)>TN(72.37%)>C/N(35.14%)>MBN(8.70%)>MBC(6.80%)>MBC/MBN(5.89%);降雨侵蚀归一化指数对Q_(10)的影响达到了79.67%.此外,任何两种因子对Q_(10)值的交互作用都要大于单一因素的单独作用.地理因素中流域与其他因素间的交互作用对Q_(10)的影响最为强烈(0.90~0.96),生化因素OC与其他因素间的交互作用对Q_(10)较强烈(0.89~0.94),气象因素中降雨和太阳辐射与其他因素交互作用对Q_(10)的影响更加不可忽略.

拉萨河流域生长期NDVI对气象因子响应的时空动态特征

拉萨河流域是青藏高原典型干旱半干旱流域,生态系统极为脆弱,研究植被指数(NDVI)对气象要素变化响应滞时的时空动态,对于探讨气候变化背景下青藏高原植被对气象因子变化的适应性具有重要意义。基于拉萨河流域1982~2017年逐月NDVI、降水量(P)、平均气温(T)数据,利用Pettitt突变及Mann-Kendall趋势检验,解析生长期NDVI及各气象因子的时空动态,并基于Pearson相关分析,识别生长期NDVI对不同气象因子响应滞时,解析气象因子对NDVI时空变化的影响。结果表明,流域尺度NDVI在1997年发生显著突变,且存在由增向减的趋势转变,流域气候由突变前的“冷湿化”向突变后的“暖干化”转变,同时其对植被生长的作用由促进转为抑制;流域内存在两条明显的NDVI对气象因子响应的滞时变化带,即流域西部多年冻土区NDVI由突变前对气象因子无响应转为突变后对P、T响应,流域南部低海拔地区NDVI对P在突变后的响应滞时较突变前延长1个月,且对T由突变前无响应转为突变后的快速响应,流域西部永久冻土区NDVI对P的响应滞时长于流域南部季节冻土区;突变后NDVI对气象因子的响应面积较突变前均有所增加,气象因子对拉萨河流域植被生长的影响作用增强。

拉萨河流域近50年来径流变化趋势分析

以拉萨水文站以上流域为研究区,基于拉萨水文站和唐加水文站的水文实测数据和当雄县等3个气象站的气候观测数据,统计分析了1956￣2003年研究区径流的年内、年际变化,利用Mann-Kendall趋势分析法和Pettitt变点检验法分析了拉萨河流域径流的变化特征,采用多元回归方法分析了气候因素(气温、降水)对径流变化的影响。结果表明:(1)研究时段内,径流年际变化波动较大,在1970年前后径流发生了较大的突变,呈现出明显的增加趋势,尤以近20年来的趋势最大;月均径流的年际变化中,有增加趋势的主要分布在冬半年(11～4月)和夏半年的个别月份(5、7、9月);(2)流域内气候变化趋势与径流变化趋势基本一致,但不同月/年均径流受不同气候因素影响,主要表现在年平均尺度上受降水影响较大,在月平均尺度上,夏半年径流增加趋势受降水增加影响较大,而冬半年径流变化则主要与气温有较显著相关性,其主要原因可能是全球变暖导致冰川融水增加。

土地覆被和气候变化对拉萨河流域径流量的影响

以拉萨水文站上游流域为研究对象,利用分布式水文模型SWAT对拉萨河流域水文过程进行模拟,分别用1995～2000和2003～2006年两个时间段的实测数据对模型进行校准和验证。结果显示月径流模拟相关系数和模拟效率系数分别为0.88和0.84。在此基础上通过建立情景模拟,探讨拉萨河流域气候波动和土地覆被变化对径流产流量的影响。结果表明:气候变化对年径流量影响显著,在各种模拟假设情景中最多可以使径流量增加89%。土地覆被变化相对于气候变化对径流量的年际影响较弱,但对径流量的季节变化影响显著。