青藏铁路沿线多年冻土区气温和多年冻土变化特征

 受气候变暖影响，青藏高原多年冻土目前处于退化状态，将会对多年冻土区的工程稳定性及生态环境产生显著影响。基于青藏铁路沿线多年冻土区4个气象站1955～2011年的气温及风火山冻土定位观测站阳坡侧15 m和阴坡侧35 m两个天然测温孔连续35年的实测地温资料，对年平均气温变化特征和多年冻土退化过程进行分析。结果表明：青藏铁路沿线多年冻土区的年平均气温从20世纪50年代后期开始逐渐升高，进入70年代后呈下降趋势，80年代中期又开始逐渐升高，2000年左右开始加剧上升，升温速率呈逐渐增大的特点；风火山地区阳坡侧多年冻土年平均地温在1978～2014年升高0.91 ℃，阴坡侧在1964～2014年升高0.58 ℃，多年冻土处于退化状态；在多年冻土的退化过程中，地温曲线类型发生着转变，阳坡侧地温曲线由最初的正梯度型转变为过渡的零梯度型，又转变为目前的负梯度型，阴坡侧地温曲线目前处于正梯度型向零梯度型过渡的阶段；阴坡侧多年冻土的退化程度远小于阳坡侧，阴阳坡冻土特征的差异主要是由寒季地温差异造成的；天然上限对年平均气温的变化较为敏感，其变化规律与气候变化规律呈显著的相关性。

Variation of temperature and permafrost along Qinghai-Tibet railway

The permafrost on the Qinghai-Tibet plateau(QTP) is degrading at present under the influence of Global Warming，which will greatly affect the stability of engineering structures and the ecosystem on the QTP. The variation of the air temperature and the process of permafrost degradation based on the air temperature in the permafrost regions on the QTP from 1955 to 2011 from four weather stations along the Qinghai-Tibet railway (QTR) were studied. The continuous ground temperatures over 35 years from two boreholes including a 15-meter- deep borehole on the sunny slope and a 35-meter-deep borehole on the shady slope of the mountain，acquired from the permafrost observational station at Fenghuoshan were analyzed. The annual mean air temperature in the permafrost regions along the QTR started to rise gradually in late 1950s，went down during 1970s，ascended back in the middle of 1980s and increased rapidly after 2000，and the rate of increasing is rising conspicuously. From 1978 to 2014，the annual mean ground temperature of the permafrost on the sunny slope of the Fenghuoshan climbed up by 0.91 ℃，and that on the shady slope also increased by 0.58 ℃ from 1964 to 2014. The permafrost is degrading because of the rising temperature. With the degradation of the permafrost，the type of geothermal temperature curves has transformed. The geothermal temperature curve of the sunny slope was changed from the initial positive geothermal gradient type to zero geothermal gradient type，then to the current minus geothermal gradient type. The geothermal temperature curve of the shady slope was changed from the initial positive geothermal gradient type to the zero geothermal gradient type. The degradation on the sunny slope is far more severe than that on the shady slope，which is mainly caused by the difference of ground temperature in cold seasons. The permafrost table is sensitive to the change of the annual mean air temperature and fluctuates with the climate change.