Articles | Volume 10, issue 4
The Cryosphere, 10, 1591–1603, 2016
The Cryosphere, 10, 1591–1603, 2016

Research article 25 Jul 2016

Research article | 25 Jul 2016

Effects of stratified active layers on high-altitude permafrost warming: a case study on the Qinghai–Tibet Plateau

Xicai Pan1, Yanping Li1, Qihao Yu2, Xiaogang Shi3, Daqing Yang4, and Kurt Roth5 Xicai Pan et al.
  • 1Global Institute for Water Security, University of Saskatchewan, 11 Innovation Boulevard, Saskatoon, SK S7N 3H5, Canada
  • 2Laboratory of Frozen Soils Engineering, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Donggang West Road 320, Lanzhou, 730000, China
  • 3CSIRO Land and Water, Christian Laboratory, Clunies Ross Street, Black Mountain, Canberra, Australian Capital Territory, 2601, Australia
  • 4National Hydrology Research Centre, Environment Canada, 11 Innovation Boulevard, Saskatoon, SK S7N 3H5, Canada
  • 5Institute of Environmental Physics, Heidelberg University, Im Neuenheimer Feld 229, Heidelberg, 69120, Germany

Abstract. Seasonally variable thermal conductivity in active layers is one important factor that controls the thermal state of permafrost. The common assumption is that this conductivity is considerably lower in the thawed than in the frozen state, λt/λf < 1. Using a 9-year dataset from the Qinghai–Tibet Plateau (QTP) in conjunction with the GEOtop model, we demonstrate that the ratio λt/λf may approach or even exceed 1. This can happen in thick (> 1.5 m) active layers with strong seasonal total water content changes in the regions with summer-monsoon-dominated precipitation pattern. The conductivity ratio can be further increased by typical soil architectures that may lead to a dry interlayer. The unique pattern of soil hydraulic and thermal dynamics in the active layer can be one important contributor for the rapid permafrost warming at the study site. These findings suggest that, given the increase in air temperature and precipitation, soil hydraulic properties, particularly soil architecture in those thick active layers must be properly taken into account in permafrost models.

Short summary
Using a 9-year dataset in conjunction with a process-based model, we verify that the common assumption of a considerably smaller thermal conductivity in the thawed season than the frozen season is not valid at a site with a stratified active layer on the Qinghai–Tibet Plateau (QTP). The unique hydraulic and thermal mechanism in the active layer challenges the concept of thermal offset used in conceptual permafrost models and hints at the reason for rapid permafrost warming on the QTP.