青藏高原多年冻土区地温年变化深度的变化规律及影响因素

地温年变化深度的准确判断对于多年冻土发育特征评估、寒区冻土模式下边界深度的确定具有重要意义.通过对青藏高原地区典型钻孔地温数据进行分析，初步揭示了多年冻土地温年变化深度的变化规律及其影响因素，并提出一种简化了地表和活动层状态影响的地温年变化深度估算方法.结果表明：研究区低温冻土的地温年变化深度平均值比高温冻土大4.6 m，随着冻土温度升高，地温年变化深度基本上呈减小趋势，部分低温冻土钻孔由于土层含水率过高导致地温年变化深度相对较小；由于活动层水热动态和冻融过程的影响，地温年变化深度与浅层（0.5 m）温度年较差相关性不显著，而与多年冻土上限附近温度年较差的大小呈显著正相关关系；地层介质的热扩散率差异是导致地温年变化深度区域差异和变化的主要原因，土层含水率、温度、质地以及水的相态是影响地层热物理性质重要因素.

Variation characteristics and impact factors of the depth of zero annual amplitude of ground temperature in permafrost regions on the Tibetan Plateau

The accurate judgment on the depth of zero annual amplitude (ZAA) of ground temperature has significant implications for estimating permafrost evolution and determining the lower-boundary depth used in climate models, land surface models or hydrological models. Based on the analysis of ground temperatures observed in 15 typical monitoring boreholes on the Tibetan Plateau, the primary variation characteristics and impact factors on the depth of ZAA are revealed and a simplified method for calculating the depth of ZAA is put forward. The results showed that the average ZAA of low-temperature permafrost is 4.6 m more than the average one of high-temperature permafrost; the ZAA decreases with the increase of permafrost temperature, but there are several boreholes with high soil moisture content bored in low-temperature permafrost regions being having relatively smaller ZAAs. Due to the effect of dynamic of heat and water and freezing and thawing process occurred in the active layer, ground temperature changing depth has no significant correlation with annual ground temperature variation in the shallow layer (0.5 m in depth), but has significant positive correlation with temperature annual range near the permafrost table. The differences of thermo-physical parameters among boreholes at different regions are the main cause of significant regional difference and variation of ZAA; the ground water content, temperature, texture and water phase state play important roles in the variation of the thermo-physical parameters of geological media. Annual variation depth of ground temperature has no significant correlation with the shallow ground temperature changes (less than 0.5 m in depth), but has significantly positive correlation with annual temperature range near the permafrost table; the differences in thermal diffusivity of stratum medium are the main reason for annual ground temperature changing depth with regional difference; the change in soil moisture content, temperature, texture and phase state of water is an important factor affecting thermo-physical properties.