青藏公路沿线多年冻土区活动层起始冻融时间的时空变化特征和影响因素
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摘要
多年冻土区活动层冻融格局对气候系统、能量平衡、水文过程和生态系统有重要的影响,地表冻融时间是反映冻融格局时空变化的重要指标。为了探明多年冻土区活动层起始冻融时间的影响因素和机制,通过对青藏公路沿线8个典型活动层观测场地表起始融化时间(OOT)和起始冻结时间(OOF)进行研究,分析了不同观测场起始冻融时间的时空差异及其影响因素。结果表明:(1)青藏高原多年冻土区活动层起始融化主要发生在4月中下旬,起始冻结主要发生在10月中下旬。OOT的年际变化幅度远大于OOF,每年起始冻结的发生较起始融化更为准时。(2)起始融化发生时的气温普遍比起始冻结发生时高1～4℃。气温对OOT的影响要比对OOF大,其中OOT的变化主要与春季气温有关,冬季气温对其影响不大。(3)植被和土壤水分对OOT和OOF有重要调节作用,土壤含水率越高,植被状况越好,起始融化和冻结的发生时间往往越迟。(4)在起始融化和冻结阶段,厚度较大和持续时间较长的积雪对地温变化有明显的抑制作用,对OOT和OOF有延迟作用。
The situation of freezing and thawing within the active layer has a vital influence on the climate system,energy balance,hydrological processes and ecological system,and the onset date of freezing and thawing is an important index to describe the spatial and temporal variations of freezing and thawing condition.In order to find out the influence factors and process on onset of freezing and thawing within the active layer,eight typical observation sites in permafrost regions along the Qinghai-Tibet Highway were selected,and their onset date of freezing(OOF) and the onset date of thawing(OOT) at each site are analyzed.The analyses showed that:(1)Within the active layer in permafrost on the Tibetan Plateau,the initial thawing occurs mainly in the middle to late April,and the initial freezing occurs mainly in the middle to late October;the annual variation of OOT is greater than that of OOF,and the freezing of the active layer occurs more regular than thawing.(2) The air temperature when the initial thawing of the active layer occurs is generally 1-4 ℃ higher than that when the initial freezing occurs;the effect of air temperature at OOT is greater than that at OOF;the variation of OOT is mainly related to the mean air temperature in spring,and barely influenced by the mean air temperature in winter.(3) Vegetation and soil moisture play an important role to OOT and OOF;high soil moisture,as well as nice vegetation,generally delays the onset of freezing and thawing.(4) When the freezing or thawing is about to start,snowcover with great depth or rather long duration obviously inhibits the rising of ground temperature and then delays the OOT and OOF,however,this is an occasional event.
The situation of freezing and thawing within the active layer has a vital influence on the climate system,energy balance,hydrological processes and ecological system,and the onset date of freezing and thawing is an important index to describe the spatial and temporal variations of freezing and thawing condition.In order to find out the influence factors and process on onset of freezing and thawing within the active layer,eight typical observation sites in permafrost regions along the Qinghai-Tibet Highway were selected,and their onset date of freezing(OOF) and the onset date of thawing(OOT) at each site are analyzed.The analyses showed that:(1)Within the active layer in permafrost on the Tibetan Plateau,the initial thawing occurs mainly in the middle to late April,and the initial freezing occurs mainly in the middle to late October;the annual variation of OOT is greater than that of OOF,and the freezing of the active layer occurs more regular than thawing.(2) The air temperature when the initial thawing of the active layer occurs is generally 1-4 ℃ higher than that when the initial freezing occurs;the effect of air temperature at OOT is greater than that at OOF;the variation of OOT is mainly related to the mean air temperature in spring,and barely influenced by the mean air temperature in winter.(3) Vegetation and soil moisture play an important role to OOT and OOF;high soil moisture,as well as nice vegetation,generally delays the onset of freezing and thawing.(4) When the freezing or thawing is about to start,snowcover with great depth or rather long duration obviously inhibits the rising of ground temperature and then delays the OOT and OOF,however,this is an occasional event.
引文
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[12]Li X,Cheng G.A GIS-aided response model of high-altitude permafrost to global change[J].Science in China:Series D Earth Sciences,1999,42(1):72-79.
[13]Wang Chenghai,Dong Wenjie,Wei Zhigang.Study on relationship between the frozen-thawprocess in Qinghai-Xizang Plateau and circulation in East-Asia[J].Chinese Journal of Geophysics,2004,46(3):309-316.[王澄海,董文杰,韦志刚.青藏高原季节冻融过程与东亚大气环流关系的研究[J].地球物理学报,2003,46(3):309-316.]
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[17]Li Ren,Zhao Lin,Ding Yongjian,et al.Temporal and spatial variations of the active layer along the Qinghai-Tibet Highway in a permafrost region[J].Chinese Science Bulletin,2012,57(35):4609-4616.
[18]Chen Boli,Luo Siqiong,LüShihua,et al.Land surface characteristics in soil freezing and thawing process on the Tibetan Plateau based on community land model[J].Journal of Glaciology and Geocryology,2017,39(4):760-770.[陈渤黎,罗斯琼,吕世华,等.基于CLM模式的青藏高原土壤冻融过程陆面特征研究[J].冰川冻土,2017,39(4):760-770.]
[19]Zhang Yu,Li Dongqing,Ming Feng.Experimental study of the freezing front movement owing to freezing-thawing cycles[J].Journal of Glaciology and Geocryology,2016,38(3):679-684.[张宇,李东庆,明锋.冻融循环作用下土体冻结锋面移动规律试验研究[J].冰川冻土,2016,38(3):679-684.]
[20]Zhang Hai'ou,Han Jichang,Zhang Yang,et al.Effects of freezing-thawing on soil aggregates of Pisha sandstone and sand compound soil[J].Journal of Glaciology and Geocryology,2016,38(1):186-191.[张海欧,韩霁昌,张扬,等.冻融交替对砒砂岩与沙复配土壤团粒结构的影响[J].冰川冻土,2016,38(1):186-191.]
[21]Henry H A L.Soil freeze-thawcycle experiments:trends,methodological weaknesses and suggested improvements[J].Soil Biology and Biochemistry,2007,39(5):977-986.
[22]Chen H,Zhu Q,Wu N,et al.Delayed spring phenology on the Tibetan Plateau may also be attributable to other factors than winter and spring warming[J/OL].Proceedings of the National A-cademy of Sciences of the United States of America,2011,108(19)[2018-05-11].https://doi.org/10.1073/pnas.1100091108.
[23]Guo Dongnan,Zang Shuying,Zhao Guangying.Effect of freezing and thawing cycles on soil microbial activity and organic carbon density in forest swamp wetland with various drainage afforestation years[J].Journal of Glaciology and Geocryology,2017,39(1):175-184.[郭冬楠,臧淑英,赵光影.冻融交替对不同年代排水造林湿地土壤微生物活性及有机碳密度的影响[J].冰川冻土,2017,39(1):175-184.]
[24]Ding Yongjian,Ye Baisheng,Liu Shiyin,et al.Monitoring and study of large scale permafrost hydrological process in Tibetan Plateau[J].Chinese Science Bulletin,2000,45(2):208-214.[丁永建,叶佰生,刘时银,等.青藏高原大尺度冻土水文监测研究[J].科学通报,2000,45(2):208-214.]
[25]Cheng Huiyan,Wang Genxu,Wang Yibo,et al.Variations of soil temperature and water moisture of seasonal frozen soil with different vegetation coverages in the source region of the YellowRiver,China[J].Journal of Lanzhou University(Natural Sciences),2008,44(2):15-21.[程慧艳,王根绪,王一博,等.黄河源区不同植被类型覆盖下季节冻土冻融过程中的土壤温湿空间变化[J].兰州大学学报(自然科学版),2008,44(2):15-21.]
[26]Liu Guangsheng,Wang Genxu,Hu Hongchang,et al.Influence of vegetation coverage on water and heat processes of the active layer in permafrost region of the Tibet Plateau[J].Journal of Glaciology and Geocryology,2009,31(1):89-95.[刘光生,王根绪,胡宏昌,等.青藏高原多年冻土区植被盖度变化对活动层水热过程的影响[J].冰川冻土,2009,31(1):89-95.]
[27]Shen M,Sun Z,Wang S,et al.No evidence of continuously advanced green-up dates in the Tibetan Plateau over the last decade[J/OL].Proceedings of the National Academy of Sciences of the United States of America,2013,110(26)[2018-05-11].https://doi.org/10.1073/pnas.1304625110.
[28]Yu H Y,Luedeling E,Xu J C.Winter and spring warming result in delayed spring phenology on the Tibetan Plateau[J].Proceedings of the National Academy of Sciences of the United States of America,2010,107(51):22151-22156.
[29]Zhang G,Zhang Y,Dong J,et al.Green-up dates in the Tibetan Plateau have continuously advanced from 1982 to 2011[J].Proceedings of the National Academy of Sciences of the United States of America,2013,110(11):4309-4314.
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