青藏高原不同时段气候变化的研究综述

1 Introduction The annual mean world temperature increased by about 0.6℃ from the late 1800s to the 1980s (Wang, 1994). The global environmental change is marked with “global warming” and its possible effects on the ecosystem as well as the production …     

阿尔金断裂带对青藏高原北部生长、隆升的制约

大量的同位素年代学证据表明(古)阿尔金断裂带可能形成于三叠纪,后又经历了侏罗纪、白垩纪的强烈左旋走滑活动,自印度板块与欧亚大陆碰撞后阿尔金断裂再次活动。主要的走滑活动发生在:(1)245~220Ma;(2)180~140Ma;(3)120~100Ma;(4)90~80Ma;(5)60~45Ma;(6)渐新世至中新世;(7)上新世至更新世以及(8)全新世。沿阿尔金断裂带,伴随左旋走滑活动形成一系列的逆冲断裂和正断裂,反映走滑过程中伴随隆升作用的存在,并且形成自北向南包括祁连山、大雪山、党河南山、柴北缘山、祁漫塔格山和昆仑山,表明阿尔金断裂带制约着青藏高原北部的生长和隆升。阿尔金断裂带东、西两端的白垩纪和新生代火山活动是断裂走滑活动的响应。     

Livelihood strategy change and land use change —Case of Danzam Village in upper Dadu River watershed, Tibetan Plateau of China

Land use change in rural China since the 1980s, induced by institution reforms, urbanization, industrialization and population increase, has received more attention. However, case studies on how institution reforms affect farmers’ livelihood strategies and drive land use change are scarce. By means of cropland plots investigations and interviews with farmers, this study examines livelihood strategy change and land use change in Danzam Village of Jinchuan County in the upper Dadu River watershed, eastern Tibetan Plateau, China. The results show that, during the collective system period, as surplus labor forces could not be transferred to the secondary and tertiary industries, they had to choose agricultural involution as their livelihood strategy, then the farmers had to produce more grains by land reclamation, increasing multiple cropping index, improving input of labor, fertilizer, pesticide and adopting advanced agricultural techniques. During the household responsibility system period, as labors being transferred to the secondary and tertiary industries, farmers chose livelihood diversification strategy. Therefore, labor input to grain planting was greatly reduced, which drove the transformation of grain to horticulture, vegetable or wasteland and decrease of multiple cropping index. This study provides a new insight into understanding linkages among institution reforms, livelihood strategy of smallholders and land use change in rural China. Foundation item: Under the auspices of National Natural Science Foundation of China (No. 40601006, 40471009), National Basic Research Program of China (No. 2005CB422006)     

5月南极涛动对青藏高原西部夏季气温影响的诊断分析

青藏高原是全球气候变暖最敏感的地区之一,是北半球夏季最大的热源,其气候响应受到广泛关注。然而,有关南极涛动与青藏高原夏季气温的关系和机理知之甚少。为了研究南极涛动与青藏高原夏季气温的关系,基于1979—2020年英国东安哥拉大学气候研究中心（CRU）的逐月气温、美国国家海洋和大气管理局（NOAA）的逐月海表面温度和大气环流再分析数据以及南极涛动指数等数据,采用相关、回归、合成分析等方法进行研究。结果表明,北半球夏季青藏高原西部气温与5月南极涛动存在显著负相关,即当5月南极涛动异常偏弱时,夏季青藏高原西部气温异常偏高。其影响过程为,南极涛动为正位相时,在南印度洋中高纬地区出现“负-正-负”的经向“三极子”海温模态,该模态可持续到夏季,在印度洋形成异常的纬向-垂直环流,相应在热带西印度洋和东印度洋-海洋性大陆之间的降水异常导致热带正“偶极子”降水模态,通过该降水模态在青藏高原西部引起异常反气旋环流和下沉运动,有利于高原西部气温偏高。研究结果显示,海洋的热惯性在“延长”南极涛动影响过程中起着重要的桥梁作用,可为青藏高原夏季气温预测提供科学依据。     

青藏高原草地地上生物量和理论载畜量

准确模拟和预测草地地上生物量(Aboveground biomass,AGB)和理论载畜量对于维持草地生态系统平衡、优化放牧管理至关重要。当前很多研究以围栏外草地AGB为基础,估算了青藏高原草地AGB的现存量。但是,牛羊啃食后的草地AGB现存量无法准确评估草地理论载畜量。围栏内草地不受家畜采食影响,其年际变率由环境因子驱动,可视为草地潜在AGB (potential AGB,AGB_p),更适用于草地理论载畜量的评估。本研究以青藏高原345个围栏内AGB观测数据为基础,结合气候、土壤和地形数据,利用随机森林算法构建草地潜在地上生物量估算模型,并对当前气候条件(2000-2018年)和未来20年(2021-2040年)4种气候变化情景(SSP1-2.6、SSP2-4.5、SSP3-7.0和SSP5-8.5)下的草地AGB_p和高寒草地理论载畜量进行模拟与预测。结果表明:(1)随机森林算法可准确模拟当前气候条件下的青藏高寒草地AGB_p(R²=0.76,P<0.001);2000-2018年青藏高寒草地AGB_p平均值为102.4 g m^-2,时间上增加趋势不明显(P>0.05);AGB_p年际波动和生长季降水显著正相关(R²=0.57,P<0.001),和生长季温度日较差显著负相关(R²=0.51,P<0.001)。(2)当前气候条件下,青藏高寒草地平均理论载畜量为0.94 SSU ha^-1(standardized sheep unit ha^-1);在过去20年约有54.1%草地理论载畜量呈提升状态。(3)和当前相比,未来20年青藏高原中部和北部草地AGB_p和理论载畜量呈下降态势。因此,建议未来在厘清气候变化影响下草畜关系的基础上进行有针对性的草牧业规划和管理,以缓解区域气候变化引起的草畜矛盾。     

用相关分析法约简MCSs空间数据库

长江流域出现致洪大暴雨与青藏高原上中尺度对流系统(MCSs)的东移密切相关。为了寻找MCSs移动和传播的规律,我们将MCSs的移动路径与其中心附近一定范围内的环境物理量场之间建立联系,构造出MCSs东移空间数据挖掘数据库。在这个数据库中,包含由9个环境物理量生成的18个属性项,除此,还包括由MCSs本身的空间特征量构成的5个属性项,即TBB强度、面积、地理位置、形状等,共计23个属性项。利用1998年6月至8月日本地球静止气象卫星(GMS)的青藏高原逐时红外遥感云图计算出的云顶黑体辐射温度(TBB)及青藏高原高分辨率有限区域数值分析预报值系统(HLAFS)环境场物理量数据,构造出上述空间数据挖掘数据库,运用空间相关分析技术对其进行约简,结果表明：在高度(H)、温度（T）、涡度(VOR)、散度(DIV)、水汽通量散度(IFVQ)、垂直速度(W）、假相当位温（θse)、K指数(K)、相对湿度(RH)等9个因素中,高度、涡度、散度、水汽通量散度、垂直速度及k指数6个因素相对独立;而温度(T)、假相当位温(θse)、相对湿度（RH)之间相关性较强,而且与高度等其它6个因素密切相关。根据数据库约简原则,可将温度（T）、假相当位温(θse)、相对湿度(RH)3个因素生成的6个属性项从数据库中删除,以便提高数据挖掘效率。     

Recent progress of glaciological studies in China

Glacier inventory compilation during the past 20 years and modifications of that for the Eastern Pamir and Banggong Lake indicate that there are 46,342 modern glaciers with a total area and volume of 59415 km2 and 5601 km3 respectively in China. These glaciers can be classified into maritime and continental (including sub-continental and extremely continental) types. Researches show that glaciers in China have been retreating since the Little Ice Age and the mass wastage was accelerated during the past 30 to 40 years. Being an important part of glaciological studies in China, ice core climatic and environmental studies on Tibetan Plateau and in the Antarctica have provided abundant, high resolution information about past climatic and environmental evolution over the Tibetan Plateau and Antarctica. Except for different parameters recorded in ice cores relating to climate and environment changes on Tibetan Plateau, records from ice cores extracted from different glaciers show that the discrepancies in climatic and environmental changes on the north and south parts of the plateau may be the consequence of different influencing effects from terrestrial and solar sources. Glaciological and meteorological phenomena imply that Lambert Glacier valley is an important boundary of climate in the east Antarctica, which is thought to be connected with cyclonic activities and Circum-polar Waves over the Antarctica.     

Atmospheric hydrological budget with its effects over Tibetan Plateau

Based on 1961-2000 NCEP/NCAR monthly mean reanalysis datasets, vapor transfer and hydrological budget over the Tibetan Plateau are investigated. The Plateau is a vapor sink all the year round. In summer, vapor is convergent in lower levels (from surface to 500 hPa) and divergent in upper levels (from 400 to 300 hPa), with 450 hPa referred to as level of non-divergence. Two levels have different hydrologic budget signatures: the budget is negative at the upper levels from February to November, i.e., vapor transfers from the upper levels over the plateau; as to the lower, the negative (positive) budget occurs during the winter (summer) half year. Evidence also indicates that Tibetan Plateau is a "vapor transition belt", vapor from the south and the west is transferred from lower to upper levels there in summer, which will affect surrounding regions, including eastern China, especially, the middle and lower reaches of the Yangtze. Vapor transfer exerts significant influence on precipitation in summertime months. Vapor transferred from the upper layers helps humidify eastern China, with coefficient -0.3 of the upper budget to the precipitation over the middle and lower reaches of the Yangtze (MLRY); also, vapor transferred from east side (27.5o-32.5oN) of the upper level has remarkable relationship with precipitation, the coefficient being 0.41. The convergence of the lower level vapor has great effects on the local precipitation over the plateau, with coefficient reaching 0.44, and the vapor passage affects the advance and retreat of the rainbelt. In general, atmospheric hydrologic budget and vapor transfer over the plateau have noticeable effects on precipitation of the target region as well as the ambient areas.