Comparison of LR,5-CV SVM,GA SVM,and PSO SVM for landslide susceptibility assessment in Tibetan Plateau area,China

The applicability of statistics-based landslide susceptibility assessment methods is affected by the number of historical landslides.Previous studies have proposed support vector machine(SVM)as a small-sample learning method.However,those studies demonstrated that different parameters can affect model performance.We optimized the SVM and obtained models as 5-fold cross validation(5-CV)SVM,genetic algorithm(GA)SVM,and particle swarm optimization(PSO)SVM.This study compared the prediction performances of logistic regression(LR),5-CV SVM,GA SVM,and PSO SVM on landslide susceptibility mapping,to explore the spatial distribution of landslide susceptibility in the study area in Tibetan Plateau,China.A geospatial database was established based on 392 historical landslides and 392 non-landslides in the study area.We used 11 influencing factors of altitude,slope,aspect,curvature,lithology,normalized difference vegetation index(NDVI),distance to road,distance to river,distance to fault,peak ground acceleration(PGA),and rainfall to construct an influencing factor evaluation system.To evaluate the models,four susceptibility maps were compared via receiver operating characteristics(ROC)curve and the results showed that prediction rates for the models are 84%(LR),87%(5-CV SVM),85%(GA SVM),and 90%(PSO SVM).We also used precision,recall,F1-score and accuracy to assess the quality performance of these models.The results showed that the PSO SVM had greater potential for future implementation in the Tibetan Plateau area because of its superior performance in the landslide susceptibility assessment.

Genesis of the Cenozoic Sodic Alkaline Basalt in the Xiahe–Tongren Area of the Northeastern Tibetan Plateau and its Continental Dynamic Implications

Objective The Cenozoic Indo-Asian collision caused significant crustal shortening and plateau uplift in the central Tibet. The extrusion tectonic model has been widely accepted to explain the strike-slip faults around the Tibetan Plateau. Previous studies indicate that the lower crust flow is the main drive force of the extrusion tectonics. Whether mantle extrusion process occurred during the Cenozoic uplift is a major problem to be addressed, which is significant for understanding the uplift mechanism and tectonic evolution of the Tibetan Plateau.

Contrasting vegetation changes in dry and humid regions ofthe Tibetan Plateau over recent decades

An overall greening over the Tibetan Plateau(TP) in recent decades has been established through analyses of remotely sensed Normalized Difference Vegetation Index(NDVI), though the regional pattern of the changes and associated drivers remain to be explored. This study used a satellite Leaf Area Index(LAI) dataset(the GLASS LAI dataset) and examined vegetation changes in humid and arid regions of the TP during 1982–2012. Based on distributions of the major vegetation types, the TP was divided roughly into a humid southeastern region dominated by meadow and a dry northwestern region covered mainly by steppe. It was found that the dividing line between the two regions corresponded well with the lines of mean annual precipitation of 400 mm and the mean LAI of 0.3. LAI=0.3 was subsequently used as a threshold for investigating vegetation type changes at the interanual and decadal time scales: if LAI increased from less than 0.3 to greater than0.3 from one time period to the next, it was regarded as a change from steppe to meadow, and vice versa. The analysis shows that changes in vegetation types occurred primarily around the dividing line of the two regions, with clear growth(reduction) of the area covered by meadow(steppe), in consistency with the findings from using another independent satellite product. Surface air temperature and precipitation(diurnal temperature range) appeared to contribute positively(negatively) to this change though climate variables displayed varying correlation with LAI for different time periods and different regions.

Morphological Characteristics of Precipitation Areas over the Tibetan Plateau Measured by TRMM PR

The multidimensional morphological characteristics(including scale, horizontal shape and 3 D morphology) of precipitation areas over the Tibetan Plateau in summer were studied using 15 years(1998–2012) of observational data from the precipitation radar onboard the Tropical Rainfall Measuring Mission satellite. As the scale of the precipitation area increased from 20 to 150 km, the near-surface rain rate(RRav) of the precipitation area increased by up to 78%(from ~1.12 to ~2 mm h~(-1)). Linear precipitation areas had the lowest median RRav(~1 mm h~(-1) over the eastern Tibetan Plateau),whereas square-shaped precipitation areas had the highest median RRav(~1.58 mm h~(-1) over the eastern Tibetan Plateau).The 3D morphology was defined as the ratio of the average vertical scale to the average horizontal scale, where a large value corresponds to thin and tall, and a small value corresponds to plump and short. Thin-and-tall precipitation areas and plump-and-short precipitation areas had a greater median RRav, whereas the precipitation areas with a moderate 3D morphology had the lowest median RRav. The vertical structure of the precipitation-area reflectivity was sensitive to both size and 3D morphology, but was not sensitive to the horizontal shape. The relationship between RRav and the morphological characteristics was most significant over the southern slopes of the Tanggula Mountains and the Tibetan Plateau east of 100°E. The morphological characteristics of precipitation areas are therefore closely related to the intensity of precipitation and could potentially be used to forecast precipitation and verify numerical models.

Atmospheric Carbon Dioxide Reconstruction and Ocean Acidification Deduced from Carbon Isotope Variations across the Triassic–Jurassic Boundary in the Qiangtang Area, Tibetan Plateau

Objective The end-Triassic mass extinction was one of the five most profound Phanerozoic extinction events.This event was accompanied by a series of significant environmental changes,of which the most notable is the emergence of warm climate and the world-wide disappearance of carbonate platform.

NO_x Release from Snow and Ice Covered Surface in Polar Regions and the Tibetan Plateau

在雪和空气之间的 NOx 的交换在大气的部件上有重要影响，在 overlying 边界 layer.Such 交换的光化学的进程增加空气的氧化能力并且可以在从冰 cores.In 被检索的空气信号上有关键影响最近的年，被日光照射了的雪和冰被表明了是在纸从雪和冰在 NOx 的版本上使彻底的评论成为的极的大气的边界 layer.This 的重要 NOx 来源。

Petrogenesis of high-Mg# Cenozoic volcanic rocks of southern Qiangtang area, Tibetan Plateau： geochemical and Sr-Nd isotopic evidence

The Nadingcuo volcanic rock suite is the most voluminous Cenozoic volcanic suite in the southern Qiangtang area of the northern Tibetan Plateau. These high-K calc-alkaline volcanic rocks were formed between36 and 34 Ma,characterized by high Mg#values,high concentrations of Ti O2 and P2O5,87 Sr /86 Sr ratios of0. 704682--0. 706 112,and εNd( t) values of- 1. 2 to 1. 6. There is a lack of reasonable explanations for sourcing and origin of magmas that formed the rocks with high Mg#values and Ti O2 and P2O5enrichments,which makes the previous research results still controversial. This study reviews the geochemical characteristics of Nadingcuo volcanic rocks and the data we have newly found in our fieldwork. We give some new interpretation to the magmatic evolution of the basaltic magmas in the discussed area dominated by fractional crystallization.The geochemistry of trachyandesite and trachyte units in the studied area is indicative of formation from mantlederived magmas that mixed with crustal materials. The high values of Mg#and Ti O2 and P2O5enrichment in these units are evident to show the mixing between mantle-derived magmas with ~ 30--40 wt.% rhyolitic melt or assimilation of a similar amount of felsic rocks. The geochemistry of basaltic rocks in the area also suggests that the Nadingcuo basalts may have been derived from an ocean island basalt( OIB)-type source that contained and was mixed with ancient mantle wedge derived material,indicating that a 36--34 Ma asthenospheric upwelling event in the Qiangtang area may relate to the northward subduction of Indian lithospheric mantle and the southward subduction of Asian lithospheric mantle. This upwelling of asthenospheric material was centered in the southern Qiangtang area between 36 and 34 Ma,while the northward movement of the Indian Craton caused this upwelling mantle flow to continuously migrate northward,resulting in the current centering of this upwelling in the Hoh Xil-Kunlun region.

Occurrence of microplastics in natural and farmland soil in the Qilian Mountains of the Northern Tibetan Plateau

Microplastics(MPs)become ubiquitous in soil and are an environmental and public health concern worldwide.However,the status of MPs in natural and farmland soils in remote areas remains poorly understood.In this study,we investigated the characteristics of MPs in natural and farmland soils along two transects in the Qilian Mountains of the northern Tibetan Plateau.The average abundance of MPs in natural and farmland soils was 29,778 and 56,123 items kg-1,respectively,with a detection size range of 10-1000μm.MPs in the size range of 10-100μm accounted for 84.1%of particles detected.Among the 21 polymers detected,polyethylene dominated in both farmland and natural soils.The shape of MPs was dominated by fragments(95.8%),followed by fibers(3.8%)and beads(0.4%).The abundance of MPs was positively correlated with increasing altitude in natural soils.There was no significant correlation between the abundance of MPs and soil physicochemical properties due to the narrow range of values of soil physicochemical properties.With the growing concern regarding MPs pollution,research on the status of MPs in high altitude and remote areas is critical to understanding their global cycle.

考虑水力连通的羌塘内流区洼地单元提取与分类

羌塘内流区是青藏高原面积最大的内流区,气候变化正在加剧其湖泊水系结构与水量的演变,开展内流区流域调查并科学估算其水资源的变化具有重要意义。本文提出一种新型内流区流域划分方法,该方法通过引入高程-面积联合阈值,以解决由气候变化与数字高程模型分辨率等因素引起的洼地单元提取难题。基于已监测的羌塘内流区流域重组与湖泊水位的变动幅度,确定了高程-面积联合阈值分别为10 m和50 km^(2),并对洼地单元进行划分,共识别出163个具有合理集水面积、永久性分水岭的封闭内流区洼地单元。引入多个相关数据集及已有算法评估本方法,结果表明:该方法适用于大尺度内流区洼地单元提取,提取精度优于现有算法及数据产品;依据洼地单元间水力连通特征,将全区163个洼地单元划分为5种主要类型,其中以“上下游互通型”(Ⅱ型)、“高山型”(Ⅳ型)洼地单元为主,“凹陷型”(Ⅴ型)洼地单元则多与其他类型复合存在,受气候条件的影响更加显著。

甘肃省甘南州牛羊焦虫病综合防控技术

牛羊焦虫病是一种常见的具有地方流行性和蜱传性的寄生虫病,对甘南州部分县市牛羊养殖业危害严重。通过对流行区域进行系统的流行病学调查及血涂片镜检,摸清并掌握牛羊焦虫病的感染情况和发病流行规律。该文就牛羊焦虫病的病原特点、临床症状、诊断、预防和治疗作以论述,旨在指导养殖户根据本地养殖特点,建立焦虫病综合防治方案,有效降低该病的发病率和死亡率。

四川高原地区表观健康藏族成人血脂合适水平的建立

目的 建立四川高原地区表观健康藏族成人胆固醇(TC)、三酰甘油(TG)、高密度脂蛋白胆固醇(HDL-C)与低密度脂蛋白胆固醇(LDL-C)的合适水平,为该地区藏族成人高脂血症的防治提供更多依据。方法 选取2022年8月至2023年7月在我院进行健康体检的藏族人群2 262例,其中男1 322例,女940例,20~69岁,检测其血脂指标(血清TC、TG、HDL-C、LDL-C)水平。对结果进行正态性检验、离群值剔除,依据美国实验室标准化协会(CLSI)C28-A3文件及国际临床化学和检验医学联合会(IFCC)相关要求,建立TC、TG、HDL-C、LDL-C的合适水平。结果 该人群中,纳入研究的血脂指标均存在男女之间的差异,TC、LDL-C随年龄增长呈上升趋势,TG、HDL-C随年龄增长变化不明显。该人群中,TC男女合适水平分别为3.03~6.60mmol/L、2.84~6.09mmol/L;TG男女合适水平分别为0.56~3.94mmol/L、0.45~2.64mmol/L;HDL-C男女合适水平分别为0.66~1.49mmol/L、0.80~1.71mmol/L;LDL-C男女合适水平分别为1.51~4.56mmol/L、1.29~3.88mmol/L。结论 初步建立了四川高原地区表观健康藏族成人血脂指标合适水平,实验室应针对此类人群建立自己的合适水平,更有利于指导临床诊断及治疗。

青藏高原东北边缘云杉-巴山冷杉林火烧迹地草本植物群落主要种生态位特征

特定环境下植物的生态位决定植物群落的相对稳定状态。以空间代替时间方法,采用Levins和Shannon-Wiener生态位宽度指数、Pianka和Schoener生态位重叠指数,分析青藏高原东北边缘云杉-巴山冷杉林火烧迹地4个演替阶段群落的种群生态位宽度和生态位重叠程度,并划分群落特化种和泛化种。结果表明:火烧迹地不同演替阶段的草本层主要物种的Levins和Shannon-Wiener生态位宽度指数结果基本一致,同一物种在不同演替阶段的生态位宽度存在差异,生态位宽度23 a>5 a>15 a>顶级群落(Climax)。5 a群落有2个特化种2个泛化种,15 a群落有4个特化种2个泛化种,23 a群落仅有3个特化种,Climax群落有3个特化种5个泛化种。23 a群落的高生态位重叠指数的种对数占比最小,而Climax群落有着较少低生态位重叠指数的种对数;中等生态位重叠指数的种对数占总对数比值大小顺序为Climax>5 a>15 a>23 a。通过研究分析可以得出:青藏高原东北边缘云杉-巴山冷杉林经过重度火干扰后,火烧迹地演替初期的群落(5 a)和受人为定向干扰的群落(23 a),植物生境资源丰富,各植物种的生态位宽度都相对较大、生态位重叠较小,相应地种间竞争小;演替中期(15 a),生态位重叠分离现象明显,群落中的大多数种在资源利用上具有极大的相似性,种间竞争加剧;而Climax属于顶级群落,各种的生态位宽度相对较宽,大多数植物种间生态位重叠不高,竞争较小,群落处于一个相对稳定的状态。除了Climax群落,其他各演替阶段群落所含特化种占特化种与泛化种之和比≥50%,特定的生境促使特化种的形成。适当的人为干预能够提高群落内种的生态位宽度,降低种间的生态位重叠,形成较为稳定的生态群落。

青藏高原东北边缘云杉-巴山冷杉林火烧迹地植物群落演替的数量研究

[目的]分析青藏高原东北边缘云杉-巴山冷杉林火烧迹地不同演替阶段植物群落物种组成和多样性变化规律,为火烧迹地植物群落的科学管理提供依据。[方法]采用空间代替时间方法,在迭山北坡,选取4个不同演替阶段的植物群落,即火后演替5年(5 a)、火后演替15年(15 a)、火后演替23年(23 a)和森林顶级群落(Climax)作为一个演替序列,采用样方法调查植物群落的物种组成,计算物种重要值、多样性指数和群落相似系数等指标,以揭示火烧迹地植物群落演替的数量特征。[结果]1)随着火烧迹地植物群落演替时间的推移,群落物种丰富度下降,个体数量逐渐减少,其中5 a群落物种丰富度最大,个体数最多(4008±298株·(400 m^(2))^(-1)),Climax的物种丰富度最小,个体数量也最少(1759±90株·(400 m^(2))^(-1));草本层5a群落、灌木层和乔木层Climax群落的Margalef指数和Shannon-Wiener指数最大。2)依据重要值,5 a、15 a、23 a和Climax 4个不同演替阶段的群落可命名为扁刺蔷薇+箭竹+密生薹草、唐古特忍冬+黑水柳+密生薹草、青海云杉-红桦+扁刺蔷薇+密生薹草群落和云杉-巴山冷杉+唐古特忍冬+密生薹草群落。3)不同演替阶段草本植物群落异质性指数5 a(0.07)<15 a(0.12)<23 a(0.19)<Climax(0.22)。4)5 a、15 a和23 a群落的多度为几何级数分布型,表明火烧迹地环境条件有利于草本植物生长,生态位确定性物种在群落构建过程中占据主要地位;而Climax群落的多度呈“S”型分布,“中间类型”物种占据了群落的绝大部分,属于演替晚期群落。5)根据β多样性的差异,可将4个不同演替阶段群落的灌木层划分为初建灌木层(5 a)和稳定灌木层(15 a,23 a,Climax),草本层划分为剧烈变化草本层(5 a和15 a)和稳定草本层(23 a和Climax)。[结论]随着植物群落演替时间越长,青藏高原东北边缘云杉-巴山冷杉林火烧迹地物种丰富度呈递减趋势,群落间的相似性越加接近,群落为正向演替,演替过程为灌木林--落叶阔叶林--针叶林--云杉-巴山冷杉林。

基于地理加权随机森林的青藏地区放牧强度时空格局模拟

精确刻画放牧强度时空格局是深刻理解青藏地区高寒草地服务功能动态及其驱动机制的重要基础,对辅助制定区域生态安全和可持续发展战略具有意义。基于牲畜年末存栏量、牧区人口密度、生长季NDVI、年降水量、年平均气温和居民点分布等数据,采用地理加权随机森林模型,模拟了2000年、2010年和2020年3期青藏地区放牧强度的空间格局,并定量评价了环境因子对放牧强度空间分布解释性的区域差异。结果表明:(1)地理加权随机森林模拟结果可精细地刻画青藏地区放牧强度的空间特征,与经典随机森林模型相比,判定系数更高,平均绝对值误差和均方根误差更低。(2)青藏地区放牧强度呈现东南高、西北低的基本特征,其中,西北部地区放牧强度低于25羊单位/km~2的区域约占青藏地区面积的1/2。(3)与2000年和2010年相比,2020年青藏地区放牧强度呈现总体下降、局部抬升的态势;其中,较2010年,2020年放牧强度下降超过1羊单位/km~2的区域占牧区面积的61.69%。(4)牧区人口密度是解释放牧强度空间异质性最主要的因素,其相对重要性呈现西高东低的特征,而降水量和生长季NDVI的相对重要性则呈现西北高、东南低的特征。研究结论可为青藏地区草地可持续管理和生态安全屏障建设提供科学参考。

青藏高原东北边缘云杉-冷杉林火烧迹地的灌木群落特征

【目的】探究青藏高原东北边缘云杉-冷杉林火烧迹地植被恢复与重建过程中的灌木群落特征动态,阐明火烧迹地灌木群落多样性格局和维持机制的生态过程,为在火烧迹地恢复与重建过程中对植被进行合理干预、尽快恢复生态效益提供合理依据。【方法】以空间代时间方法,分析恢复5年和15年火烧迹地灌木群落和未过火林地林下灌木层物种组成特征、α物种多样性和β物种多样性。【结果】在5年、15年火烧迹地灌木群落与未过火林地林下灌木层之间,植物种类组成存在差异,5年火烧迹地共调查到11科17属24种,15年火烧迹地共调查到8科10属17种,未过火林地共调查到12科19属35种。5年、15年火烧迹地和未过火林地的物种丰富度指数与Pielou均匀度指数,以及5年火烧迹地的物种丰富度指数与Simpson指数、物种丰富度指数与Shannon-Wiener指数的相关性均不强(P<0.1或P>0.1),其他指数间的相关性均较强(P<0.001或P<0.01)。物种丰富度指数为5年火烧迹地>15年火烧迹地>未过火林地,Shannon-Wiener指数和Simpson指数均为15年火烧迹地>未过火林地>5年火烧迹地,Pielou均匀度指数为15年火烧迹地>未过火林地>5年火烧迹地。5年、15年火烧迹地灌木群落的物种组成最相似,未过火林地林下灌木层物种组成和15年火烧迹地灌木群落的相似度大于5年火烧迹地。【结论】青藏高原东北边缘云杉-冷杉林经重度林火干扰后,在不同恢复时间梯度上的物种组成存在差异。火后短时间内局部生境范围内物种丰富度增加,火烧迹地的物种多样性和优势度较低,物种分布不均匀。随着演替进行,物种丰富度减小,物种多样性和优势度上升,物种分布较均匀。随着火烧迹地演替正常进行,火烧迹地与未过火林地物种组成相似度增加,火烧迹地灌木群落朝着正向演替。

青藏高原东北边缘云杉-巴山冷杉林火烧迹地草本植物群落构建机理

群落构建机制是生态学研究的核心论题。生态位理论和中性理论是阐明群落构建的两种主要理论,但这两种理论分别强调的环境过滤和扩散限制对群落构建的影响尚存争议。该研究以青藏高原东北边缘云杉-巴山冷杉林火烧迹地不同演替阶段草本群落为研究对象,应用扩散-生态位连续体指数(DNCI)和校正随机率(MST),分析不同演替阶段草本植物群落的主导构建机制。研究结果显示:1)5、15和23 a群落与Climax群落之间的DNCI分别为-22.6169、-21.7507和-8.2594,都远小于0,表明不同演替阶段草本植物群落构建的主要驱动作用是扩散过程;2)5 a-Climax组和23 a-Climax组的MST值均高于50%阈值线,这表明随机性过程在两组群落构建中均占支配地位;对于15 a-Climax组,15 a的MST值为0.6664,Climax的MST值等于0.4927,说明15 a植物群落构建以随机性为主,而Climax群落构建以确定性为主;由于15 a的MST值远高于50%,而Climax的MST值较接近于50%的阈值,也可说明15 a-Climax组群落构建仍以随机性为主。在青藏高原东北边缘云杉-巴山冷杉林火烧迹地,随机扩散主导了草本植物群落的构建过程。

青藏高原阿里地区大气颗粒物质量浓度的季节变化特征

基于2018-12-01至2019-11-30在中国科学院阿里荒漠环境综合观测研究站颗粒物监测仪的数据,获得了大气颗粒物质量浓度及其季节变化特征.研究结果表明,PM10、PM_(2.5)、PM1在观测期间的日均质量浓度分别为(10.51±8.62)μg·m^(−3)、(4.05±2.36)μg·m^(−3)和(2.47±1.56)μg·m^(−3),低于青藏高原城市地区.PM_(2.5)、PM10远低于国家规定的颗粒物年平均一级浓度限值(GB 3095—2012),表明阿里地区洁净的大气本底特征.阿里地区污染源稀少,气象因子成为影响颗粒物浓度变化的重要因素.尽管阿里地处西风和印度季风的过渡带,西南季风显著影响了阿里站颗粒物浓度变化,季风带来的暖湿气团使季风期颗粒物浓度显著降低;加之边界层高度等气象因素的季节变化,使大气颗粒物浓度呈现明显的季节变化规律,冬季和季风前大于季风期和季风后期.阿里站处于高寒荒漠环境,大气颗粒物以粗颗粒为主,PM_(2.5)/PM10的平均比值为0.39,与其他地点对比,比值偏低.聚类分析表明,阿里站主要受偏西气团影响.潜在源贡献因子分析(PSCF)和浓度权重轨迹分析(CWT)分析结果表明,PM10、PM_(2.5)、PM1主要潜在源区均分布在印度西北部、巴基斯坦北部.由于监测原理的不同和气象因子的影响,MODIS AOD数据与颗粒物浓度数据在12月、7月和8月差异较大,遥感获取的气溶胶参数需要进一步订正提高在高原的适用性.

Pliocene cyprinids (Cypriniformes,Teleostei) from Kunlun Pass Basin,northeastern Tibetan Plateau and their bearings on development of water system and uplift of the area

Here described are the cyprinid fossils from the Pliocene Lower Member of Qiangtang Formation of the Kunlun Pass Basin,northeastern Tibetan Plateau,collected at a locality 4769 m above the sea level(asl).The materials consist of numerous disarticulated and incomplete bones as well as thousands of pharyngeal teeth,fin rays,and vertebrae.The fossils were referred to the genus Gymnocypris,lineage Schizothoracini,family Cyprinidae;the lineage Schizothoracini;and the family Cyprinidae respectively.The Schizothoracini is a freshwater fish group endemic to the Tibetan Plateau and its surrounding area.Previous workers on living schizothoracins regarded that Gymnocypris belongs to the highly specialized grade of the group,colonizing higher altitudes than other members of the group.Two species are so far unequivocally assigned to the genus,i.e.,G.przewalskii and G.eckloni,and they are inhabiting Qinghai Lake and the waters on both north(the Golmud River) and south(upper reach of the Yellow River) sides of the East Kunlun Mountain,respectively.The abundant fossil schizothoracins occur in the Kunlun Pass Basin on the southern slope of the East Kunlun Mountain(at 4769 m asl),close to the present Golmud River,indicating comparatively rich waters in the area and possible connections between the water systems on north and south sides of the East Kunlun Mountain during the Pliocene.This also suggests a more humid climate in the area during the Pliocene than it is today.The presence of the highly specialized schizothoracin Gymnocypris may also imply less amplitude of uplift(approximately 1000 m) in the area since the Pliocene than previously proposed.

Land use dynamics in Lhasa area, Tibetan Plateau

Land use change is the result of the interplay between socioeconomic, institutional and environmental factors, and has important impacts on the functioning of socioeconomic and environmental systems with important tradeoffs for sustainability, food security, biodiversity and the vulnerability of people and ecosystems to global change impacts. Based on the results of the First Land Use Survey in Tibet Autonomous Region carried out in the late 1980s land use map of Lhasa area in 1990 was compiled for the main agricultural area in Lhasa valley using aerial photos obtained in April, May and October 1991 and Landsat imagery in the late 1980s and 1991 as remotely sensed data sources. Using these remotely sensed data the land use status of Lhasa area in 1991, 1992, 1993, 1995, 1999 and 2000 were mapped through updating annual changes of cultivated land, artificial forest, grass planting, grassland restoration, and residential area and so on. Land use map for Lhasa area in 2007 was made using ALOS AVNIR-2 composite images acquired on October 24 and December 26, 2007 through updating changes of main land use types. According to land use status of Lhasa area in 1990, 1995, 2000 and 2007, the spatial and temporal land use dynamics in Lhasa area from 1990 to 2007 are further analyzed using GIS spatial models in this paper.

Dust storms and loess accumulation on the Tibetan Plateau: A case study of dust event on 4 March 2003 in Lhasa

Whether the Tibetan Plateau is a significant dust source area is of great importance, because this is re-lated to the understanding of sources, accumulation and environmental effects of dusts on the Tibetan Plateau and in the Far East-Pacific Ocean regions as well as to the evolution of coupling of the Tibetan Plateau and atmosphere-ocean- continent exchange. Synoptic dynamics and remote sensing tracing of a dust storm on 3 to 5 March, 2003 in Lhasa on South Tibet demonstrate that the Tibetan Plateau possesses all factors and conditions of generating dust storms. Accom-panied with this dust storm is a strong ascending stream on the Plateau which has raised various sizes of dust particles into different levels. The lifted coarse particles were largely fallen down and accumulated as loess on the eastern Tibetan Plateau, and the fine particles were translated by the west-erly jet and subsided in the northern Pacific Ocean. The spa-tial-temporal distribution of dust-storms between years 1961 and 2000 on the Plateau shows that dust-storms mainly occur in winter and early spring with high frequency, and the path of dust storm moves gradually from south to north, which is closely coupled with the northward moving of the westerly jet from winter to spring over the Tibetan Plateau. Com-pared with other twelve dust source areas in China, the Ti-betan Plateau is one of the key dust source areas for the long-distance transport because its high occurring frequency and elevation cause fine particles easily to be lifted into the zone of the westerly jet.