Variation in the permafrost active layer over the Tibetan Plateau during 1980–2020

The active layer, acting as an intermediary of water and heat exchange between permafrost and atmosphere, greatly influences biogeochemical cycles in permafrost areas and is notably sensitive to climate fluctuations. Utilizing the Chinese Meteorological Forcing Dataset to drive the Community Land Model, version 5.0, this study simulates the spatial and temporal characteristics of active layer thickness (ALT) on the Tibetan Plateau (TP) from 1980 to 2020. Results show that the ALT, primarily observed in the central and western parts of the TP where there are insufficient station observations, exhibits significant interdecadal changes after 2000. The average thickness on the TP decreases from 2.54 m during 1980–1999 to 2.28 m during 2000–2020. This change is mainly observed in the western permafrost region, displaying a sharp regional inconsistency compared to the eastern region. A persistent increasing trend of ALT is found in the eastern permafrost region, rather than an interdecadal change. The aforementioned changes in ALT are closely tied to the variations in the surrounding atmospheric environment, particularly air temperature. Additionally, the area of the active layer on the TP displays a profound interdecadal change around 2000, arising from the permafrost thawing and forming. It consistently decreases before 2000 but barely changes after 2000. The regional variation in the permafrost active layer over the TP revealed in this study indicates a complex response of the contemporary climate under global warming. 活动层是多年冻土和大气之间的缓冲层, 对气候波动十分敏感, 且它的冻融变化对多年冻土区的地球生物化学循环有较大影响.本研究利用高分辨率气象数据集CMFD和陆面过程模式CLM5.0模拟分析了青藏高原1980–2020年活动层的变化.结果表明:青藏高原的活动层厚度在2000后有显著的年代际变化, 青藏高原整体活动层厚度由1980–1999的2.54 m减少到2000-2020年的2.28 m.这种变化主要发生在西部的多年冻土区, 与东部相比存在明显的区域差异.在东部, 多年冻土区的活动层厚度呈持续增加趋势, 而不是年代际变化.此外, 活动层面积在2000年也发生了年代际突变, 之前持续下降, 但之后几乎没有变化.我们还发现青藏高原多年冻土活动层的区域变化受到气温和降水等环境因子的显著影响, 这反映了其在全球变暖背景下对气候变化的复杂响应.