关键词: 冻土分布, 多年冻土热稳定性, 年均地温, 黄河源

Abstract:

The source area of the Yellow River (SAYR) is located in the eastern-to-medium part of the Qinghai-Tibet Plateau. Permafrost in the SAYR experienced remarkable degradation in the past. Taking distribution patterns of frozen soil and permafrost stability as research object, the characteristics of permafrost development and distribution patterns at various terrains and land covers were analyzed based on a large amount of field investigations and the measurements. In addition, thermal features of permafrost were analyzed based on the measured ground temperatures at various depths. The effects of the geological and geographic factors on permafrost distribution and thermal stability were discussed. It was indicated that: 1) Permafrost was occasionally developed in the various fluvial and proluvial plains with elevation generally lower than 4 300 m; 2) Permafrost was widely distributed in the mountains higher than 4 350 m except for the sunny slope terrain, where local terrain played an important role in permafrost development and distribution; 3) The combinations of local terrain, surficial vegetation, soil wetness and moisture conditions all contributed to the formation and distribution of permafrost in the low hills and mountains where elevation ranged in 4 300-4 350 m.Taking the annual mean ground temperature (MAGT) as the basis, an experiential-statistical MAGT-based model was constructed, of which latitude, longitude and elevation were set up as independent variables. Together with DEM data, permafrost MAGTs were primarily modeled using the statistically regression model. And then, the modeled results in the south-facing areas were slightly adjusted, and a secondly model was constructed to model permafrost distribution in the shady areas. Thirdly, the combined modeling results were locally adjusted using the measurements. The frozen soil map in the SAYR was thus compiled. Taking 0oC as the boundary between permafrost and seasonally frozen soil, it was indicated that permafrost was distributed in an area of 2.5×10⁴km², which occupied approximately 85.1% in the SAYR, and that seasonally frozen soil was distributed in an area of 0.3×10⁴km² with an areal percentage of 9.7%. Permafrost was further divided into seven stability taking 0.5oC or 1.0oC of MAGTs as intervals.They were the first zone with permafrost MAGT smaller than -4.0oC, the second zone with permafrost MAGT varying between -4.0oC and -3.0oC, the third zone with permafrost MAGT varying between -3.0oC and -2.0oC, the fourth zone with permafrost MAGT varying between -2.0oC and -1.0oC, the fifth zone with permafrost MAGT varying between -1.0oC and -0.5oC, the sixth zone with permafrost MAGT varying between -0.5oC and 0oC, and the seventh zone with permafrost MAGT higher than 0oC.

Key words: permafrost distribution, permafrost thermal stability, mean annual ground temperature, the source area of the Yellow River