为探究怒江源区季节冻土的冻融特性，选取源区 4 个典型试验场 5?cm 表层土壤中发生的短历时冻融事件作 为研究对象，明确事件内涵、提出事件具体判别方法并对事件发生的特性进行评价。评价内容由起止时间、总历 时、总次数、循环频率、强度共 5 项组成。其中在强度评价，采用 Copula 函数法联合温差、湿差、历时 3 个单一指 数构建更全面高效的综合指数，并针对冻结和冻融两个不同的过程分别进行评价。研究表明：怒江源区不同地理 位置的短历时冻融事件特性具有差异，中海拔区（4?500～5?000?m.a.s.l.）的事件比低海拔区（<4?500?m.a.s.l.）和高海 拔区（>5?000?m.a.s.l.）的事件呈现出总历时更长、总次数更多、循环频率更高、累加强度更大的特征规律；高频或 高强的事件能够极大影响甚至破环土壤环境，对此更应注重怒江源区北部区域的冻融监测和防护；冻结和冻融是 两个强度效应不同的过程，分别评价可避免强度被削弱的问题。研究成果有利于明晰高原寒区季节冻土冻结及 融化的特性，进而体现短历时冻融事件的影响，为源区水土保持、冻胀与融塌危害防控提供支撑。

Seasonally frozen soil is widely distributed in Qinghai-Tibet Plateau and soil freeze-thaw events occur frequently in the headstream of Nujiang River. Due to the large altitude difference and the asynchrony of meteorological changes between different regions in the headstream region, the occurrence of freeze-thaw events has different characteristics and certain regularities in time and space.To explore the characteristics of freeze-thaw in seasonally frozen soil, the short-duration freeze-thaw events that occurred in the 5 cm surface soil of 4 typical experimental fields of the headstream region were selected. The connotation of the short-duration freeze-thaw events was clarified and a specific identification method for these events was proposed. The characteristics of events were evaluated and the evaluation was formed by five aspects: The start and end time, the total duration, the total number of times, the cycle frequency, and the intensity. In the intensity evaluation, the Copula function method was used to combine three single indexes of temperature difference, humidity difference, and duration to construct a more comprehensive and efficient comprehensive index, and the two different processes of freeze and freeze-thaw are evaluated separately.The evaluation results showed that from September 1, 2019, to August 31, 2020, the short-duration freeze-thaw events in the 4 typical experimental fields had a maximum difference of 45 days in the start time and 64 days in the end time. The maximum difference in the total duration, the total number of times and the cycle frequency can reach 112 days, 79 times, and 0.058 times/day, respectively. The maximum difference in the cumulative intensity and the maximum intensity can reach 50.991 and 0.034 for the freezing process, 50.991 and 0.034 for the freeze-thaw process.The characteristics of short-duration freeze-thaw events in different geographical locations in the headstream of Nujiang River are different. The events in the middle-altitude area ( 4 500 - 5 000 m.a.s.l.) showed regularity with a longer total duration, higher total number of times, cycle frequency, and accumulation intensity than the events in the low-altitude area (< 4500 m.a.s.l.) and the high-altitude area (> 5 000 m.a.s.l.). High-frequency or high-intensity events can greatly affect or even destroy the soil environment. In this regard, more attention should be paid to freeze-thaw monitoring and protection in the northern part of the basin. Freeze and freeze-thaw were two processes with different intensity effects, and evaluated respectively can avoid the problem of weakened strength. The results are conducive to clarifying the freeze-thaw characteristics of seasonally frozen soil in the plateau alpine region, and reflecting the impact of short-duration freeze-thaw events, providing support for water and soil conservation, frost heaving, thaw collapsing hazards prevention and control in the headstream.