Abstract: Based on the monthly soil moisture of GLDAS Noah 2.0 from 1950 to 2009, the temporal and spatial variation characteristics of soil moisture at each layer of the Tibetan Plateau in summer were analyzed. The results are as follows: (1) In summer, the soil moisture at each layer of the Tibetan Plateau decreased gradually from south to north, and there was an extreme value center at the middle and deep layers in the central of the Tibetan Plateau, respectively. (2) The difference of soil moistures between the surface, shallow, middle and deep layers (except for the deep and middle layers) in summer appeared a vertical distribution of ‘wet upper and dry lower’ in the mid-eastern part of the Plateau, while that showed a vertical distribution of ‘wet lower and dry upper’ in the mid-western part. (3) The first mode of soil moisture at different layers of the Plateau in summer appeared a reverse distribution from southwest to northeast, and the zero line moved to northeast with the increase of soil depth. (4) The annual variation characteristics of soil moisture at different layers of the main part of the Plateau were obvious in summer during 1950-2009. The soil moisture except for the deep layer had significant downward trend as a whole, and it was higher in the early stage and lower in the later stage from 1950 to 2009, while for the deep layer it appeared non-significant increasing trend. Spatially, the decreasing trend of soil moisture at different layers except for deep layer of the Plateau dominated during 1950-2009, while the soil moisture at deep layer of the central part of the Plateau tended to increase. (5) After removing trend, the maximum variation range of annual average soil moisture at each layer except for the deep layer decreased with the increase of soil depth in the central part of the Plateau, while it increased with the increase of soil depth in the central and eastern part of the Plateau.

Key words: Tibetan Plateau, soil moisture, global land data assimilation system, temporal and spatial variation

摘要： 基于1950—2009年GLDAS Noah 2.0逐月平均土壤湿度资料，分析了夏季青藏高原各层土壤湿度的时空变化特征。结果表明：（1）夏季青藏高原各层土壤湿度整体上呈自南向北递减的空间分布，但在高原中部地区中层、深层土壤湿度均有一个极值中心。（2）夏季高原中东部地区表层、浅层、中层、深层土壤湿度之间的差值（深层与中层除外）均表现为“上湿下干”的垂直分布，而中部偏西地区各层土壤湿度差值则表现为“下湿上干”的垂直分布。（3）夏季高原各层土壤湿度第一模态均呈现西南—东北反向型分布，且随着深度的增加，零线向东北移。（4）夏季高原主体各层土壤湿度的年际变化特征明显，除深层（呈现不显著增加趋势）外整体均呈现显著下降趋势，前期土壤湿度较高，后期较低。从空间趋势分布来看，除深层土壤湿度在高原中部有增大趋势外，各层土壤湿度变化趋势在高原上均以减小为主。（5）去趋势后，除深层外其他各层土壤湿度最大年际变化幅度在高原中部随着土层的增加而减小，而高原中东部则随土层的增加而增大。

关键词: 青藏高原, 土壤湿度, GLDAS, 时空变化