Multi-Layer Soil Temperature Distribution and Its Variation Characteristics in the Past 45 Years in Xinjiang

A dataset obtained at 87 stations in the Xinjiang Uygur Autonomous Region is used to analyze the spatial distribution of and temporal changes in multilayer soil temperature and climate variables (precipitation, sunshine duration, and surface air temperature). The results showed that: (1) The geographical distribution of the July soil temperature in the Xinjiang region exhibited higher values in the south than in the north and higher values on the plains than in the mountains. The shallow soil temperature in Xinjiang was high, with a maximal value of 38 ℃, but the deep soil temperature was low, only 15 ℃ in northern Xinjiang. Southern Xinjiang and the Junggar Basin in northern Xinjiang have a wider distribution of soil temperature differences between the shallow and deep layers, whereas the soil temperature differences in the Tianshan Mountains and the northern mountainous region were smaller. (2) The surface soil temperature has undergone three phases in the past 45 years: A decline in the mid-1960s to the 1970s, rapid warming in the mid-1970s to the early 1980s, and a slow decline after the 1980s. The surface soil temperature (0 cm) changed abruptly around 1978, but not the soil temperature at other layers. (3) The July soil temperature gradient in Xinjiang has also undergone three phases: A decline in the mid-1960s to the 1970s, rapid growth in the mid-1970s to early 1980s, and a slow decline after the 1980s. The rate of growth in the rapid growth period of the 1980s was 0.0176 ℃ cm^-1 a^-1. The McDonald-Kreitman test revealed that the soil temperature gradient increased significantly after 1978. (4) The interannual variation in the multilayer soil temperature was negatively correlated with precipitation and positively correlated with sunshine duration and surface air temperature. The strength of the correlation between the three meteorological factors and the soil temperature could be ordered as follows, from high to low: Surface air temperature, precipitation, sunshine duration. Further, the shallow soil temperature is more strongly correlated with the meteorological factors than the deep soil temperature.