Spatiotemporal characteristics of the soil freeze-thaw state and its variation under different land use- A case in Northeast China

With global warming, the soil freeze-thaw state has greatly changed, which has profoundly impacted the balance between water resources, ecological security and regional agriculture and forestry production in frozen regions. Based on daily soil freezing/thawing depth data in Heilongjiang Province over the last 60 years, Mann-Kendall trend analysis, Sen's slope and Hurst exponent were performed to analyze the spatiotemporal characteristics of the soil freeze-thaw state, and the effects of nonclimatic factors land use types and snow cover on the change in the soil freeze-thaw state were discussed. The results indicated that (1) the soil freeze-thaw state significantly changed over the past 60 years. The maximum seasonally frozen depth decreased approximately by 48 cm, the first freezing date was delayed by approximately 10 d, the first thawing date and last date advanced approximately by 6 and 27 d, respectively, the freezing and thawing periods decreased by approximately 17 and 21 d, respectively, and the duration and actual number of freezing days decreased by 38 and 34 d, respectively. (2) The soil freeze-thaw state changed abruptly in 1988 and exhibited a significant trend after the 1990s. The Hurst exponent of the soil freeze-thaw state variables at approximately 2/3 of the stations reached the strong persistence level. (3) In forestland and grassland areas, vegetation coverage reduced the climate warming impact on the soil freeze-thaw state. In addition, the maximum snow depth was significantly correlated with the soil freezing depth and first thawing date, and the change in snow depth also offset the effects of temperature rise on soil freezing depth and first thawing date to a certain extent. Changes in the soil freeze-thaw state have both advantages and disadvantages on agricultural production. Therefore, it is necessary to strengthen agricultural monitoring and use territorial knowledge to reasonably regulate agricultural production.

Automated summary

Global warming has significantly altered the freeze-thaw state of soil in frozen regions, impacting water resources, ecological security, and agricultural production. Analysis of data over the past 60 years showed a decrease in frozen depth and changes in freezing/thawing dates, with implications for agricultural monitoring and regulation. This highlights the need to address the effects of climate change on soil conditions and agricultural production.