Influence of microtopography on active layer thaw depths in Qilian Mountain, northeastern Tibetan Plateau

Climate warming over the Tibetan Plateau has been thickening the active layer, the most significant indicator of the permafrost system. This study evaluates the influence of microtopography on active layer thaw depth in recent years at Eboling basin of the eastern Qilian Mountain, northeastern Tibetan Plateau. Thaw depths were measured at microtopographic levels in 2012, 2013, and 2014, respectively. Watershed-scale sampling was used to estimate the influence of various morphologies on the active layer, while a second sampling scheme to examine the variations in the frost table height along six short transects. A third sampling scheme used spatial autocorrelation analysis in a regular grid at 10 × 10 m intervals. The results documented that microtopography (elevation, microrelief, surface configuration, and slope) played a pivotal role on the active layer thickness of mountainous permafrost in the study area. Active layer became thinner in depressions, which was contrary to most of Arctic sites. Spatial autocorrelation analysis elucidated that the dominant topographic factors controlled the changes of active layer thickness. These factors exerted the majority of control over the spatial variations of the active layer. The results can help researchers or engineers to roughly estimate the probable influence of micromorphology on the changes in thickness of the active layer in mountainous permafrost regions in the Tibetan Plateau.