Characteristics of water and heat change during the freezing-thawing process of soil profiles in the alpine cold steppe, Northern Tibetan Plateau

To understand the soil freezing-thawing cycle of alpine meadows in northern Tibet, we monitored the hydrothermal characteristics of alpine grassland soil profiles between 2015 and 2016, based on the Xianzha alpine grassland and wetland ecosystem observation station, and discussed the relationship between the freeze-thaw process and meteorology. The results showed that the soil temperature and moisture in each layer underwent sinusoidal periodic change, and the amplitude of the change varied with the depth. The soil freezing period extended from the beginning of November to the end of April of the next year, and the maximum depth of freezing was about 160 cm. According to the patterns of soil freezing and thawing, the freezing-thawing period was divided into four stages: initial freezing, stable freezing, early ablation, and late ablation. There was a significant correlation between the upper/lower freezing depths and accumulated temperature.