土壤冻融过程是青藏高原陆面过程中最突出的特征之一， 量化表征土壤冻融过程的关键参量变化特征对认识青藏高原气候变化、 生态和水文过程有重要的科学意义。本文利用青藏高原地区ECMWF/ERA5（European Centre for Medium-Range Weather Forecasts/ERA5）的浅层土壤温度、 体积含水量和气温资料， 通过线性回归、 Mann-Kendall检验法、 滑动t检验和相关分析等方法， 分析了表征青藏高原土壤冻融过程的三个关键参量-冻结开始时间、 融化开始时间和冻结持续时间的时空分布特征， 并探讨了其与气温、 海拔的相关性。结果表明： 青藏高原土壤冻融过程的空间分布特征为由西北到东南存在冻结推迟、 融化提前和冻结持续时间缩短的趋势。1979 -2018年间， 青藏高原整体土壤冻融过程改变显著， 冻结开始时间推迟14.0天， 变率为0.17 d·a^-1； 融化开始时间提前11.0天， 变率为0.07 d·a^-1； 冻结持续时间缩短25.0天， 变率为0.23 d·a^-1。青藏高原土壤冻融过程整体变化趋势一致， 局地变率存在差异。羌塘地区土壤冻结持续时间缩短最为明显， 南北部分别缩短47.2天和32.9天。三个冻融过程关键参量与气温、 海拔相关性显著。气温每上升1.0 ℃， 冻结开始时间推后5.2天， 融化开始时间提早4.5天。在青藏高原高寒气候带， 海拔每升高1000.0 m， 冻结开始时间提早9.1天， 融化开始时间推后4.9天。

The freeze-thaw process is one of the most prominent features of the land surface process on the Qinghai-Xizang Plateau， and quantifying the variation of the key variables that denote the soil freeze-thaw process has scientific significance for understanding the climate change， hydrological processes and ecosystems of the Qinghai-Tibetan Plateau.By using the ECMWF/ERA5 （European Centre for Medium-Range Weather Forecasts/ERA5） reanalyzed soil temperature， volumetric soil water and air temperature data， the temporal and spatial trends of the start date of soil freezing， the start date of soil thawing and the duration of the soil freezing and their relationships with the air temperature and altitude were investigated by using linear regression， Mann-Kendall test， moving t test and correlation analysis.These results demonstrated that the spatial distribution of soil freeze-thaw process in the Qinghai-Xizang Plateau is characterized by a trend of delaying freeze， advancing thaw and shortening freeze from the northwest to the southeast.The soil freeze-thaw process varied significantly on the Qinghai-Xizang Plateau from 1979 to 2018.The start date of soil freezing was delayed by 14.0 days with a rate of 0.17 d·a^-1， and the start date of soil thawing was advanced by 11.0 days with a rate of 0.07 d·a^-1， and the duration of the soil freeze was shortened by 25.0 days with a rate of 0.23 d·a^-1 over the past 40 years.The overall trend of soil freeze-thaw process is the same in the Qinghai-Xizang Plateau， while the local rate is different.Throughout the period of study， the duration of the soil freeze in the southern and the northern Changtang Plateau is shortened by 47.2 days and 32.9 days.The first date of the soil freeze， the first date of the soil thaw and the duration of the soil freeze are significantly correlated with temperature and altitude.If the air temperature rises by 1.0 ℃， the first date of the soil freeze will be delayed by 5.2 days， and the first date of the soil thaw will be advanced by 4.5 days， so that the duration of the soil freeze will be shortened by 9.8 days.In the high cold Tibetan climatological zone， the first date of the soil freeze will be advanced by 9.1 days， and the first date of the soil thaw will be delayed by 4.9 days， while the duration of the soil freeze will be increased by 13.9 days as the altitude increases by 1000.0 m.