Influence of slope direction on the permafrost degradation: a case study
in Qinghai-Tibetan Plateau
Abstract
Slope direction affects permafrost degradation because of its influence
on the surface energy balance. The ground thermal difference between
slopes of differing aspect is known, however there are few detailed
reports on differences in soil temperature, humidity, and radiation from
slopes in permafrost areas that caused permafrost degradation. In this
study variations in air and ground thermal regime were compared at two
sloping sites with opposing aspect in a permafrost region of the
Qinghai-Tibetan Plateau (QTP). The results indicate that air
temperatures (Ta) were similar at both sites in September 2016-19.
However, ground temperatures, including the ground surface temperature
(Ts), the temperature near the permafrost surface (Tps), and the
permafrost temperature at 5.0 m depth (Tg), and soil moisture content
within the active layer differed greatly between sites. The mean annual
Ts, Tps, and Tg over three years (2016-19) were 1.3-1.4 ℃ higher at the
sunny slope than at the shady slope. The near-surface soil moisture
content during the thawing season was 10-13% lower at the sunny slope
(~22-27%) than the shady slope
(~35-38%), and was significantly and negatively
correlated with ground temperature. Shortwave downward radiation (DR) at
the sunny slope was higher than at the shady slope. However, net
radiation (Rn) was lower at the sunny slope due to the greater surface
albedo at the site. The results highlight a complex spatial pattern of
ground thermal conditions in mountainous permafrost regions, help define
the climate-permafrost relation in the region, and for understanding
permafrost degradation on a local scale.