Impact of a retrogressive thaw slump on surrounding vegetation communities in the Fenghuoshan mountains,Qinghai-Tibet Plateau

Under global warming,permafrost around the world is experiencing degradation which is especially so on the Third Pole,the Qinghai-Tibet Plateau(QTP),China.Retrogressive thaw slump(RTS)is one of the thermokarst features caused by rapid degradation of ice rich permafrost,which transforms landforms and threatens infrastructures,and even affects the terrestrial carbon cycle.In this work,vegetation communities surrounding a RTS in the Fenghuoshan Mountains of the interior portion of the Qinghai-Tibet Plateau have been investigated to examine the impact from RTS.This investigation indicates that the occurrence of RTS influences the vegetation community by altering their habitats,especially the soil water content,which forces the vegetation community to evolve in order to adapt to the alterations.In the interior part of RTS where it has been disturbed tremendously,alterations have produced a wider niche and richer plant species.This favors species of a wet environment in a habitat where it was a relatively dry environment of alpine steppe prior to the occurrence of RTS.This study adds to limited observations regarding the impact of RTS to vegetation community on the QTP and helps us to reach a broader understanding of the effects of permafrost degradation as well as global warming.

Calculation method for thickness of discontinuous boundary layer of engineering pavement

The boundary layer is a buffer layer of water and heat exchange between the atmosphere and permafrost. Based on the atmospheric boundary layer and heat transfer theory, we established a method for determining the boundary layer thickness of engineering pavement （asphalt and sand pavement） in permafrost region. The boundary layer can be divided into the Boundary Layer Above Surface （BLAS） and the Boundary Layer Below Surface （BLBS）. From in-situ monitoring data, the thickness of BLAS was determined through the laminar thickness, and the thickness of BLBS was determined through ground temperature, the heat conduction function, and the mean attenuation function （α）. For asphalt pavement, the BLAS thickness varied between 2.90 and 4.31 mm and that of BLBS varied between 28.00 and 45.38 cm. For sand pavement, the BLAS thickness varied between 2.55 and 3.29 mm and that of BLBS varied between 15.00 and 46.44 cm. The thickness varied with freezing and thawing processes. The boundary layer calculation method described in this paper can provide a relatively stable boundary for temperature field analysis.

Human thermal comfort under lateral radiant asymmetries

Occupants’thermal comfort in buildings may be affected by the cool wall and warm wall,which is attributed to the effect of asymmetric radiation.However,the previous majority of the researches on asymmetric radiation were mainly about the comfort limits under thermally neutral condition within 1∼1.5 h but had not considered the effect of exposure duration and the condition beyond neutral.To investigate the human thermal comfort under an asymmetric environment caused by the cool wall and warm wall,forty-four subjects were exposed to neutral air temperature with lateral radiant asymmetries in winter and summer for 3 h.The results indicated that the cool wall caused thermal discomfort easier than the warm wall because the thermal sensation decreased and deviated from neutral with time.Subjects’sensitivity of local parts to asymmetric radiation was affected in the conditions beyond neutral,thus their acceptability to asymmetric radiation decreased.The currently used limits of radiant temperature asymmetry tended to underestimate the local discomfort due to the walls.For the conditions tested,The limits of 5%dissatisfaction in radiant temperature asymmetry were 4.4°C(180 min)and 1.8°C(60 min and 120 min)for the warm wall,and 1.8°C at 60 min for the cool wall.