Spatio-Temporal Variation of Freezing-Thawing State of Near Surface Soil in the Three-Rivers Headwater Region of Tibetan Plateau,China
Freezing-thawing process of near-surface soil comprises the exchange of moisture and energy between soil and atmosphere,whose dynamic change could be used for scientific interpretation of degradation in permafrost.Possibly restricted by the acquisition of surface observation data in high-altitude plateau areas of China,more scientific efforts were made to reveal the characteristics of soil thermal-hydrological transporting in the midst of freezing-thawing in permafrost,but attentionally neglected the long-term change trend of soil freezing-thawing and associated spatio-temporal change.The Three-Rivers Headwater Region in the Tibetan Plateau of China was extensively occupied by perennial permafrost,which is a climate-sensitive area and critical zone for global climate change.In this study,it collected field observations at 23 national meteorological stations in the Three-Rivers Headwater Region and at other 6 stations set in active layer of permafrost for examination of the accuracy of ERA5-Land ground temperature data;then it analyzed the change of soil freezing-thawing from 1980 to 2021 and associated spatio-temporal change.(1)The average value of correlation coefficient between ERA5-Land surface soil temperature data and the observed data by 23 meteorological stations was 0.94,with a mean value of the mean-root-square error was 4.49 ℃.The average value of correlation coefficient between ERA5-Land surface soil temperature data and the data collected at other 6 stations set in active layer of permafrost was 0.96,with a mean value of the mean-root-square error was 2.57 ℃.The data from ERA5-Land could meet research requirements for evaluating of soil freezing-thawing changes in the Three-Rivers Headwater region.(2)The spatial distribution of annual mean temperatures of surface soil over a year was high in the east and low in the west in the Three-Rivers Headwater region;near-surface soil temperatures increased the most in the summer and the least in the fall,with overall higher increases in the spring and summer than in the fall and winter.(3)From 1980 to 2021,the number of freezing days and freezing duration in the Three-Rivers Headwater region had a significant decreasing trend,with a rate of 4.99 d/10a and 6.77 d/10a,respectively.The start of freezing was delayed,with a rate of 3.43 d/10a;the end of freezing was advanced,with a rate of 3.35 d/10a.(4)The vegetation coverage in the western high-altitude area of the Three-Rivers Headwater region was much lower than that in the eastern low-altitude area,which may be an key reason for the decrease of freezing days in the low-altitude area was lower than that in the high-altitude area.This study introduced a general knowledge of the spatio-temporal changes of topsoil freezing-thawing in the Three-Rivers Headwater region by application of ERA5-Land data,which provides an insight into the spatial degradation characteristics of permafrost in the Tibetan Plateau.
the Three-Rivers Headwater regionERA5-Landsoil freezing-thawingspatio-temporal change
万方数据
维普
