1971-2016年青藏高原积雪冻土变化特征及其与植被的关系

利用1971-2016年青藏高原81个气象站逐月积雪日数和45个测站第一冻结层下界观测资料，分析了青藏高原积雪冻土的时空变化特征及其与高原植被指数（NDVI）的关系，探讨了积雪冻土下垫面变化对高原植被及沙漠化的可能影响。结果表明：1）青藏高原积雪日数分布极不均匀，巴颜喀拉山和唐古拉山为高原积雪日数的大值区，且年际变率较大。2）青藏高原积雪日数总体上呈现减少趋势，平均以3.5 d/（10 a）的速率减少，且在1998年前后发生突变，减少速率进一步加快，达到5.1 d/（10 a）。3）青藏高原第一冻结层下界呈上升趋势，达到-3.7 cm/（10 a），与青藏高原增暖紧密相关。4）青藏高原NDVI呈缓慢增加趋势，与高原气温、降水的增加趋势相一致，积雪冻土的变化对不同区域植被NDVI的影响有显著差异。在气候变暖背景下，形成的暖湿环境促进积雪消融、冻土下界提升，使土壤浅层含水量增加，有利于植被恢复和生长，其结果对高原土地沙漠化防治有一定参考作用。

Variation characteristics of snow cover and frozen soil and their relationships with vegetation in the Tibetan Plateau from 1971 to 2016

As forcing factors of land surface,the snow cover and frozen soil play important roles in the climate system.Based on the monthly snow cover days of 81 meteorological stations and the observation data of the lower boundary of the first frozen layer of 45 stations in the Tibetan Plateau from 1971 to 2016,the temporal and spatial variation characteristics of snow cover and frozen soil in the Tibetan Plateau and their relationships with NDVI (Normalized Difference Vegetation Index) were analyzed.The possible influence of changes in the underlying surface of snow cover and frozen soil on the vegetation and desertification in the Tibetan Plateau were also discussed.Results show that:(1)The distribution of snow cover days in the Tibetan Plateau is extremely uneven.The Bayan Har and Tanggula mountains are high value areas of snow cover days in the plateau,and their interannual variabilities are large.(2)There is a decreasing trend of snow cover days in the Tibetan Plateau from 1971 to 2016,and the average reduction rate is 3.5 d/(10 a).A sudden change of the snow cover days occurs around 1998,and the reduction rate is further accelerated to 5.1 d/(10 a).(3)The lower boundary of the first frozen layer in the Tibetan Plateau from 1971 to 2016 shows an upward trend,reaching -3.7 cm/(10 a),which is closely related to the warming of the Tibetan Plateau.(4)NDVI in the Tibetan Plateau is increasing slowly,which is consistent with the increasing trend of temperature and precipitation.The effect of snow cover and frozen soil changes on NDVI in different regions of the Tibetan Plateau has significant difference.Under the background of climate warming,the warm and humid environment promotes the melting of snow and the lifting of the lower boundary of the first frozen layer.Further,the water content of shallow soil layers increases,which is conductive to vegetation restoration and growth.The results have a certain role in the study of land desertification on the Tibetan Plateau.