Variations in precipitation effects on shallow soil of seasonally frozen ground during different freeze-thaw stages

With the ongoing effects of climate warming and wetting, the impact of precipitation on freeze-thaw processes in frozen ground is gaining significance. Nevertheless, the influence of precipitation during different freeze-thaw stages on the thermal regime of shallow soil remains poorly understood on seasonally frozen ground (SFG). Here, based on the data observed at the Madoi and Maqu sites on SFG from 2014 to 2018, we analyzed the response of soil hydrothermal characteristics and freeze-thaw duration to the precipitation during different freeze-thaw stages. The relationship between soil hydrothermal characteristics and precipitation was weak on an annual scale. Interannual differences in the start and end of the freezing stage (FS) are mainly caused by variations in precipitation, which directly affect the soil liquid water content at both sites. An additional 28 mm of precipitation during the same two-month period encompassing FS postponed the start of freezing by 27 days and shortened the duration of FS by 14 days at Madoi site. Precipitation differences were minimal at Maqu site, the FS showed less variability. Furthermore, the contrasting responses between Madoi and Maqu can be attributed to differences in soil properties. The low soil ice content during the completely frozen stage (CFS) can be attributed to either low precipitation during the FS or high snowfall during CFS at Madoi site. Lower air and soil temperature after the beginning of soil freeze resulted in the higher soil ice content at Maqu site. The prolonged snow cover delayed soil thawing at the two sites. Compared to the FS, the thawing stage (TS) was more susceptible to the influence of snow cover due to the melting and infiltration of snow. Different snow melting patterns can significantly affect the soil thawing process.