. The near-surface soil freeze/thaw status is an important indicator of climate change. Using data from 636 meteorological stations across China, we investigated the changes in the first date, the last date, the duration, and the number of days of the near-surface soil freeze over the period 1956–2006. The results reveal that the first date of the near-surface soil freeze was delayed by about 5 days, or at a rate of 0.10 ± 0.03 day yr−1, and the last date was advanced by about 7 days, or at a rate of 0.15 ± 0.02 day yr−1. The duration of the near-surface soil freeze decreased by about 12 days or at a rate of 0.25 ± 0.04 day yr−1, while the actual number of the near-surface soil freeze days decreased by about 10 days or at a rate of 0.20 ± 0.03 day yr−1. The rates of changes in the near-surface soil freeze/thaw status increased dramatically from the early 1990s through the end of the study period. Regionally, the changes in western China were greater than those in eastern China. Changes in the near-surface soil freeze/thaw status were primarily controlled by changes in air temperature, but urbanization may also play an important role.\n

Located at the eastern margin of the Tibetan Plateau, the source region of the Yellow River is an important ecological security shelter for economic development in Southwest China, with its unique natural habitats and abundant natural resources. Based on the data of 18 meteorological stations within and around the source region, map of China vegetation types (1:1000,000) and DEM data, and using the methods of trend analysis, relative inter-annual variation and correlation analysis, we selected MODIS evapotranspiration (ET) as the main data source to research the spatio-temporal characteristics of ET and its variation under different land use types as well as its relationship with climate factors in the study area from 2000 to 2014. The results indicate that: (1) the regional differentiation of mean ET over years is obvious, the northern ET is significantly weaker than that of the central and southeastern parts, and the strongest ET is observed in the southeastern part. The multi-year mean value of ET is 538.61 mm/a, and the anomaly relative variation is obvious. In addition, the trend of inter-annual variation of ET decreases firstly and then increases, and the trend variation rate is 0.44 mm/a. (2) During the study period, the ET shows a periodic unimodal trend and peaks in July. Moreover, seasonal differences of ET are apparent in the source region of the Yellow River, and the highest value of ET reaches 188.14 mm/a in summer, followed by spring and autumn, yet the lowest is only 97.15 mm/a in winter. (3) From 2000 to 2014, the value of ET in different types of land use has a similar regular pattern, namely: wetland > forest > grassland > other types > bare land. On the whole, the value of ET in each type of land use increases gradually. (4) According to the correlation analysis results, there are positive correlations between ET and air temperature, as well as between ET and precipitation, while ET has a negative correlation with relative humidity. The effect of precipitation on ET is stronger than that of air temperature. Furthermore, the result of ET driven by different factors demonstrates that the climate-driven region of ET is predominantly precipitation-driven in the source region of the Yellow River.

黄河源区地处青藏高原东缘,具有独特的自然生境和丰富的自然资源,是中国西南区域经济发展的重要生态安全屏障。以MODIS ET产品作为研究黄河源区地表蒸散发（ET）的数据源,结合黄河源区内部及周边18个气象站数据、全国1∶100万植被类型图和黄河源区DEM数据,利用趋势分析、相对年际变化和相关分析法,研究2000-2014年黄河源区ET时空变化特征及不同土地利用类型下ET的变化规律,重点探讨了ET与气候因子的关系。结果表明：① 黄河源区多年ET区域分异规律明显,北部ET显著弱于中部和东南部,最强ET位于黄河源区的东南部,多年平均ET值为538.61 mm/a,距平相对变化显著,ET年际变化呈先减小后增加的趋势,平均趋势变化率为0.44 mm/a;② 年内ET呈周期性单峰变化趋势,7月达到峰值;2000-2014年黄河源区多年四季ET季节性差异明显,夏季ET最强达到188.14 mm/a,春秋季次之,冬季ET最弱仅97.15 mm/a;③ 研究时段内不同土地利用类型的ET大小表现为沼泽地>林地>草地>其他>裸地,整体上各土地利用类型的ET呈逐渐增加趋势;④ 相关分析结果表明,ET与同期气温、降水呈正相关关系,与相对湿度呈负相关关系,其中降水对ET的影响强于气温;驱动分区结果显示黄河源区ET受气候因子驱动的地区主要表现为降水驱动。

土壤冻融过程在寒区水文和气候系统中有着重要作用。陆面模式中土壤冻融过程的参数化对模式的设计和模拟结果有着关键作用。通过对广泛应用的Bucket，SIB，BATS，VIC，BEAS， LSM等几种主要的陆面模式中的冻融过程参数化方案进行了总结和比较。首先，详尽地描述了土壤冻融与气候变化的数值模拟研究，总结和评述了土壤冻融过程对气候变化的作用。其次，对几种主要的陆面过程模式在土壤水热参数化方案中对冻融过程的考虑及其特点进行了比较和讨论。还对冻结深度和冻结周期的预报模式进行了简介，最后对该领域当前面临的主要研究问题进行了探讨和阐述。

Vegetation recovery under global change and its consequent evolution of eco-hydrological processes have modulated the water resources conservative capacity in the source region of the Yellow River (YRSR). Based on climatological data, remotely sensed vegetation index and geographical information, the integrated simulations of water and carbon cycles in the YRSR are presented, with the vegetation interface processes (VIP) distributed eco-hydrological dynamic model. Then the co-evolving mechanisms of hydrological and vegetation dynamics are investigated. Results show that warming and wetting climate in the YRSR has improved the vegetation growing condition and extended the growing period for more than 10 days in recent decades. Averaged NDVI from 2010 to 2020 increased by 4.5% relative to that from 2000 to 2009. Vegetation gross primary productivity (GPP) shows a significant uptrend with a rate of 4.57 gC m-2 a-1, 77% of which is contributed by climate change and elevated atmosphere CO2 fertilization, and the rest 23% is by vegetation greening. Evapotranspiration (ET) is increasing at a rate of 2.54 mm a-1 and vegetation water use efficiency (WUE, expressed as GPP/ET) is also improving at a relative rate of 5.1% a-1. Generally, annual ET, GPP and WUE and their trends are decreasing along the elevation below 4200 m. At basin scale, there are significant positive correlations between the vegetation greenness and the runoff coefficient with precipitation in the current and previous years, demonstrating a legacy effect of precipitation for vegetation recovery on water conservation capacity. The increased ET might be a benefit to the water recycle between land surface and atmosphere, which will alleviate the reduced potential of water yield owing to ecological restoration and establish trades-off and synergies among precipitation, vegetation and water yield. Conclusively, exploring the mechanisms of hydrological responses to climate change and vegetation recovery and its feedback will provide scientific support to the assessment of ecological engineering programs in the source regions.

全球变化下黄河源区水文过程的演变影响流域生态系统的水源涵养功能,流域植被改变也影响水循环。本文基于气候、植被信息和VIP分布式生态水文模型,开展黄河源区水碳循环要素变化的集成模拟,分析了气候—植被—水文要素的协同演变机制。结果表明,2000年以来黄河源区气候呈暖湿化趋势;植被绿度明显提高,2010—2019年比2000—2009年平均增加了4.5%;生长季延长了至少10 d;植被生产力（GPP）显著上升,倾向率为4.57 gC m^-2 a^-1;植被恢复措施对GPP变化的贡献约为23%,气候变化和大气CO₂升高的施肥效应的贡献为77%。源区植被蒸散量（ET）呈增加趋势,倾向率为2.54 mm a^-1,水分利用效率（WUE）亦提高,平均相对上升率为5.1% a^-1。GPP、ET和WUE年总量及其变化率在海拔4200 m以下随高度上升而减小,之后变化趋缓。源区植被绿度和径流系数与当年和前一年降水呈显著正相关,反映降水蓄存于植物根层土壤的遗留效应。蒸散增强在一定程度上有利于源区地表—大气之间的水分再循环,帮助缓解生态恢复引起的产水能力下降,促进降水—植被—径流之间的良性互馈关系的形成。揭示水文对气候变化和植被恢复的响应和互馈机制,可为生态恢复措施对源区水源涵养功能的影响及效应的定量评估提供科学依据。

Air and ground freezing thawing index for stations in the Heihe River Basin were calculated based on daily mean temperature, and its variation characteristics and time series were analyzed. The results showed that, the freeing index over the Heihe River Basin were influenced by elevation and latitude while the thawing index mainly influenced by elevation;air freezing-thawing index and surface freezing-thawing index ranges were 673~2 135℃·d,1 028~4 177 ℃·d,682~1 702 ℃·d,1 956~5 278 ℃·d, respectively; freezing index exhibited decreasing trend and the slopes of air freezing index (1951—2007) and surface freezing index (1954—2005) were -56.0 ℃·d /10a and -35.4 ℃·d /10a; thawing index increased and the liner tendency of air thawing index was 47.8 ℃·d/10a during 1951—2008; surface thawing index decreased during 1954—1975 with a rate of -135.9 ℃·d /10a and increased during 1976—2006 with a rate of 185.3 ℃·d /10a. Freezing index was influenced by both elevation and latitude while thawing index was mainly controlled by elevation in the Heihe River Basin. We also found that there was a strong liner relationship between mean annual air temperature and freezing-thawing index.

利用黑河流域气象站点的逐日平均温度数据计算空气及地表冻融指数,并分析其变化趋势以及空间分布。结果表明,黑河流域空气冻结指数、空气融化指数、地表冻结指数和地表融化指数变化范围依次为：673~2 135 ℃·d,1 028~4 177 ℃·d, 682~1 702 ℃·d,1 956~5 278 ℃·d;黑河流域冻结指数出现明显的下降趋势,其中空气冻结指数（1951—2007年）下降速率为56.0℃·d/10a,地表冻结指数（1954—2005年）下降速率为35.4 ℃·d/10a;融化指数表现为上升,其中空气融化指数（1951—2008年）整体以每年47.8 ℃·d/10a的速率上升,地表融化指数在1954—1975年以135.9 ℃·d/10a的速率下降,在1976—2006年以185.3 ℃·d/10a的速率上升;黑河流域各站点冻结指数受海拔及纬度双重影响,而融化指数则主要受海拔影响;年平均气温与冻融指数有非常强的线性关系。

The source area of the Yellow River (SAYR) is located in the eastern-to-medium part of the Qinghai-Tibet Plateau. Permafrost in the SAYR experienced remarkable degradation in the past. Taking distribution patterns of frozen soil and permafrost stability as research object, the characteristics of permafrost development and distribution patterns at various terrains and land covers were analyzed based on a large amount of field investigations and the measurements. In addition, thermal features of permafrost were analyzed based on the measured ground temperatures at various depths. The effects of the geological and geographic factors on permafrost distribution and thermal stability were discussed. It was indicated that: 1) Permafrost was occasionally developed in the various fluvial and proluvial plains with elevation generally lower than 4 300 m; 2) Permafrost was widely distributed in the mountains higher than 4 350 m except for the sunny slope terrain, where local terrain played an important role in permafrost development and distribution; 3) The combinations of local terrain, surficial vegetation, soil wetness and moisture conditions all contributed to the formation and distribution of permafrost in the low hills and mountains where elevation ranged in 4 300-4 350 m.Taking the annual mean ground temperature (MAGT) as the basis, an experiential-statistical MAGT-based model was constructed, of which latitude, longitude and elevation were set up as independent variables. Together with DEM data, permafrost MAGTs were primarily modeled using the statistically regression model. And then, the modeled results in the south-facing areas were slightly adjusted, and a secondly model was constructed to model permafrost distribution in the shady areas. Thirdly, the combined modeling results were locally adjusted using the measurements. The frozen soil map in the SAYR was thus compiled. Taking 0oC as the boundary between permafrost and seasonally frozen soil, it was indicated that permafrost was distributed in an area of 2.5×104km2, which occupied approximately 85.1% in the SAYR, and that seasonally frozen soil was distributed in an area of 0.3×104km2 with an areal percentage of 9.7%. Permafrost was further divided into seven stability taking 0.5oC or 1.0oC of MAGTs as intervals.They were the first zone with permafrost MAGT smaller than -4.0oC, the second zone with permafrost MAGT varying between -4.0oC and -3.0oC, the third zone with permafrost MAGT varying between -3.0oC and -2.0oC, the fourth zone with permafrost MAGT varying between -2.0oC and -1.0oC, the fifth zone with permafrost MAGT varying between -1.0oC and -0.5oC, the sixth zone with permafrost MAGT varying between -0.5oC and 0oC, and the seventh zone with permafrost MAGT higher than 0oC.

以黄河源区多年冻土分布现状和热力特征为研究目标,通过野外调查及实测数据,分析了黄河源区不同地形地貌、不同地表覆盖条件下的冻土形成、分布特征和以地温为基础的热学特征,探讨了不同尺度因素对多年冻土分布的影响。结果表明,在高程低于4 300 m的平原区,多年冻土多不发育;在高于4 350 m的山区,局地地形对多年冻土的形成与分布作用显著。除阳坡地形外,多年冻土均比较发育;介于4 300~4 350 m的低山丘陵和平原区,局地地形、地表植被、土壤湿度等因素共同决定着多年冻土的形成和分布格局。以年均地温指标为基础,构建了以纬度、经度和高程为自变量的回归模型,并对阳坡地形进行微调和校正。结果表明,以0oC作为划分季节冻土和多年冻土的标准和界限,多年冻土面积2.5×10⁴km²,约占整个源区面积的85.1%;季节冻土面积0.3×10⁴km²,约占整个源区面积的9.7%。进一步以0.5oC或1.0oC为分类间隔绘制了黄河源区多年冻土热稳定性空间分布图。

The numerical simulation method was used to predict the future possible changes that happened on permafrost by setting up the prediction results of the climate model from the IPCC Fifth Assessment Report as a possible climatic condition. The source area of the Yellow River with complicated permafrost conditions was chosen as the study area. The past and future permafrost distribution were predicted, and the future possible changing trends in permafrost in this area were calculated. The obtained results were, (1) during the past 30 years of 1972-2012, a small part of permafrost was degraded, which covered an area of about 833 km2. In this period, the seasonal frozen soil type was mainly distributed in the of Requ river valley, Xiaoyemaling, and Tangchama, as well as the southern part of the two lake basins. (2) Under different climatic scenarios of RCP 2.6, RCP 6.0 and RCP 8.5, little difference would happen on permafrost degradation until 2050. In details, the possible degradation area of permafrost would be 2224 km2, 2347 km2, and 2559 km2 under the scenarios of RCP 2.6, RCP 6.0, and RCP 8.5, respectively, accounting for 7.5%, 7.9%, 8.6% of the total study area. The seasonal frozen soil type would be sporadically distributed in the river valleys of Lena Qu, Duo Qu, Baima Qu, but widely distributed around Yeniugou, Yeniutan and four Madio lakes located in the Yellow River valley in the eastern part of Ngoring Lake. (3) In 2100, the predicted permafrost degradation area would be 5636 km2, 9769 km2 and 15548 km2, respectively, and they would account for 19%, 32.9% and 52.3% of the source area. The permafrost degradation mainly occurred in the areas of Xingsuhai, Gamaletan, Duogerong, of which low-temperature permafrost would be degraded into a high-temperature permafrost type. And the mean annual ground temperature of permafrost would rise differentially. (4) Under the scenario of RCP 2.6, all permafrost with current mean annual ground temperature higher than -0.15oC would be degraded into seasonal frozen soil type, and the permafrost with the mean annual ground temperature ranging from -0.15 oC to -0.44oC would be partly degraded into seasonal frozen soil type. Under the scenarios of RCP 6.0 and RCP 8.5, permafrost with the current mean annual ground temperature higher than -0.21 oC and -0.38 oC would be totally degraded, the permafrost with the mean annual ground temperature ranging from -0.21 to -0.69 oC and from -0.38 oC to -0.88 oC would be partly degraded.

基于IPCC第五次评估报告预估的气温变化情景,采用数值模拟的方法对黄河源区典型冻土类型开展模拟,推算过去及预测未来黄河源区冻土分布空间变化过程和发展趋势。结果表明：1972-2012年源区多年冻土只有少部分发生退化,退化的冻土面积为833 km²,季节冻土主要集中在源区东南部的热曲谷地、小野马岭以及两湖流域南部的汤岔玛地带;RCP 2.6、RCP 6.0、RCP 8.5情景下,2050年多年冻土退化为季节冻土的面积差别不大,分别为2224 km²、2347 km²、2559 km²,占源区面积的7.5%、7.9%、8.6%;勒那曲、多曲、白马曲零星出现季节冻土,野牛沟、野马滩以及鄂陵湖东部的玛多四湖所在黄河低谷大片为季节冻土;2100年多年冻土退化为季节冻土的面积分别为5636 km²、9769 km²、15548 km²,占源区面积的19%、32.9%、52.3%;星宿海、尕玛勒滩、多格茸的多年冻土发生退化,低温冻土变为高温冻土,各类年平均地温出现了不同程度的升高。到2100年,RCP 2.6情景下源区多年冻土全部退化为季节冻土主要发生在目前年平均地温高于-0.15 oC的区域,而-0.15~-0.44 oC的区域部分发生退化;RCP 6.0、RCP 8.5情景下目前年平均地温分别为高于-0.21 oC以及-0.38o C的区域多年冻土全部发生退化,而-0.21~-0.69 oC以及-0.38~-0.88 oC的区域部分发生退化。

The hydrological and meteorological data of the source region of Yellow River from 1956 to 2010 and future climate scenarios from regional climate model (PRECIS) during 2010-2020 are used to analyze the flow variations and revealing the climate causes, and to predict the variation trend for future flows. Some conclusions can be drawn as follows. 1) Annual mean flow shows a decreasing trend in recent 50 years in the source region of Yellow River, and there are periods of 5a, 8a, 15a, 22a and 42a. 2) The precipitation decrease due to the weakened South China Sea summer monsoon as well as the increasing evaporation and the degenerating frozen soil in global warming are the climate origin of decreasing flow. 3) Based on the regional climate model PRECIS prediction, the flows in the source region of Yellow River are likely to decrease in the next 20 years.

There is an obvious three-dimensional zonation in the distribution of high-altitude per-mafrost, namely, vertical, latitudinal and aridity (or longitudinal) zonation.

多年冻土南界以南一定的海拔高度以上出现的多年冻土称为高海拔多年冻土,而南界以北的多年冻土则叫作高纬度多年冻土。

The soil freeze-thaw cycle plays an important role in land surface processes. Repeated freeze-thaw cycles can have profound effects on land-atmosphere energy exchange, surface runoff, plant growth, ecosystems and soil carbon & nitrogen cycles. Using spatial analysis functions of geographical information system and python programming language, this paper analyzed the spatial distributions and temporal variations of soil freeze-thaw state in Northeast China based on the ERA5-LAND hourly soil temperature dataset for the period 1981-2019. The results suggest that the start dates of the four soil freeze-thaw periods for the near-surface layer are mainly determined by latitude and topography. The start dates of freeze-thaw transition period in spring (SFTTP) and complete thawing period (CTP) show a southeast-northwest gradient with later starts in the northwest part, while the start dates of freeze-thaw transition period in autumn (AFTTP) and complete freezing period (CFP) exhibit a latitudinal pattern with earlier starts in the north. For most parts of the study area, the average annual number of days for SFTTP is less than 30, with higher values in the south and west compared to the north and east. The number of days for AFTTP, however, is below 10 per year for most parts of the region, with just a slight difference in the study area. The CTP is the longest compared to the other three periods, varying from 150 days in the northwest to 240 days in the southeast. The CFP, which comes next, ranges from 90 to 180 days per year, presenting a dustpan-shaped spatial pattern with higher values in the north and lower values in the south. Trend analysis shows that with the advance of start date for SFTTP and the delay of start date for AFTTP, the number of days for CTP has increased with a rate of 0.2 d/a. The number of days for SFTTP in the Liaohe Plain, the western part of the Da Hinggan Mountains and the northern part of Hulun Buir Plateau shows a decreasing trend, while in other regions an increasing trend is observed. In the western part of the Da Hinggan Mountains and the northern part of the Hulun Buir Plateau, the CTP starts earlier. The start date of AFTTP is significantly delayed in the Songnen Plain and Changbai Mountains, and the trend for the number of days varies substantially with an increase in the north and a decrease in the south. The start date for CFP occurs later in the vast area of the Northeast China Plain and occurs earlier in the Da Hinggan Mountains, Xiao Hinggan Mountains, Changbai Mountains, Eastern Liaoning Peninsula and Western Liaoning Hills. The number of days for CFP shows a declining trend throughout the study area, especially in the seasonally frozen area located in the central part with an annual decreasing rate of more than 0.2 d/a.

土壤冻融交替是陆地表层极其重要的物理过程,土壤冻融状态的频繁变化对地气能量交换、地表径流、植被生长、生态系统及土壤碳氮循环等均具有重要的影响。本文基于1981—2019年ERA5-LAND逐小时土壤温度数据,借助GIS空间分析功能,利用Python编程处理分析了中国东北地区近地表土壤冻融状态的时空变化特征。结果表明：从不同冻融状态起始日期的空间分布来看,近地表不同阶段的起始日期主要受纬度和地形的影响,具有明显的纬度地带性和垂直地带性。春季冻融过渡期和完全融化期的起始日期由东南向西北均呈逐渐推迟趋势,而秋季冻融过渡期与完全冻结期起始日期则由东南向西北随纬度升高越来越早。就不同冻融状态发生天数的空间分布而言,研究区南部春季冻融过渡期发生天数多于北部,西部多于东部,年均发生天数均在30 d以内;秋季发生冻融的天数空间差异不大,研究区一半以上的地区年均发生天数在10 d以内。完全融化期发生天数最多,从东南向西北呈逐渐减少趋势,年均发生天数主要介于150~240 d之间;完全冻结期发生天数则由南向北日益增多,其空间分布表现为一向南开口的簸箕形,各地年均发生天数集中于90~180 d之间。从时间变化趋势来看,近年来春季冻融过渡期起始日期以提前趋势为主,而秋季冻融过渡期起始日期总体表现为延后,致使完全融化期发生天数以增加趋势为主,年均变化速度高达0.2 d/a;大兴安岭以西、呼伦贝尔高原以北地区及辽河平原春季冻融过渡期发生天数呈减少趋势,其他地区为增加趋势;大兴安岭以西地区、呼伦贝尔高原以北地区完全融化期起始日期明显提前;松嫩平原和长白山区秋季冻融过渡期起始日期推迟显著,发生天数的变化趋势呈北增南减的空间分异特征;不同地区完全冻结期起始日期的变化趋势差异显著,中部广大的平原区呈不显著的推迟趋势,而大、小兴安岭、长白山、辽东半岛和辽西丘陵则提前进入完全冻结状态;研究区完全冻结期发生天数呈减少趋势,研究区中部的季节冻土区完全冻结期明显变短,年均减少速度大于0.2 d/a。

Based on the surface soil daily minimum temperature and air temperature datas from 87 meteorological stations over the Qinghai-Tibetan Plateau (QTP), the trends of the near-surface freeze-thaw status and its correlation with air temperature, altitude and latitude was analyzed by using the linear regression method and correlation method.Using Mann-Kendall method to test the abrupt change and discuss the spatial variation characteristics of the near-surface soil freeze-thaw status over QTP.The results show that the near-surface soil freeze-thaw status changed significantly on QTP in recent 36 years.The first date of the near-surface freeze was delayed by about 26 days, or at a rate of 0.72 d·a^-1, and the late date of the near-surface freeze was advanced by about 14 days, or at a rate of 0.40 d·a^-1.The number of duration days and freeze days of the near-surface freeze decreased about 41 and 33 days respectively, and the rate of change was 1.13 d·a^-1 and 0.93 d·a^-1, respectively.The trend of the near-surface soil freeze-thaw status was same overall QTP, while in some areas was slight differences.The central and eastern region of QTP, the first date of the near-surface freeze was earlier and the last date was later than other regions.However, there was a contrary variation in the southeast region.It may be the lower elevation of the stations and it had the higher air temperature all years.For the change rate of the near-surface soil freeze-thaw status, the eastern part of QTP changed the fastest, the western was moderate and the stations that changed slower scattered in central and southern regions.The temperature had a significant effect on the near-surface soil freeze-thaw status, but air temperature had a certain lag effect on soil freeze-thaw cycle.And the near-surface soil freeze-thaw status was great significantly correlated with altitude.With decreasing elevation, the first days of the near-surface soil freeze was delayed and the late days was advanced, and the numbers of duration days and freeze days of the near-surface soil freeze were significantly decreased.

利用青藏高原（下称高原）87个气象台站的日最低地表温度和气温资料，通过线性回归和相关分析法，分析高原1980-2015年近地表土壤冻融状况变化趋势及其与气温、海拔和纬度的相关性。利用Mann-Kendall检验对其进行突变分析，并探讨其空间变化特征。结果表明：近36年，高原近地表土壤冻融状况发生显著变化。冻结起始时间推迟约26天，其变化速率为0.72 d·a^-1，冻结结束时间提前约14天，速率为0.40 d·a^-1；冻结持续时间和冻结天数分别缩短约41天和33天，其变化速率分别为1.13 d·a^-1和0.93 d·a^-1。高原冻融状况变化整体表现一致，局部地区略有差异。高原中东部地区冻结起始时间较早，结束时间较晚；而在东南部地区则存在相反的变化特征，这是由于该地区海拔较低，且全年土壤温度较高导致。就冻融状况变化速率而言，东部地区变化最快，西部适中，变化较慢的站点零星分布在中部和南部地区。气温对近地表土壤冻融状况有重要影响，但气温对土壤冻融循环存在一定的滞后作用。此外，高原近地表土壤冻融状况与海拔呈极显著相关，随海拔的降低，冻结起始推迟，冻结结束时间提前，冻结持续时间和冻结天数显著减少。