GRL: 青藏高原冬季变暖对多年冻土的影响研究

被誉为世界“第三极”的青藏高原是全球中低纬度地区海拔最高、面积最大的多年冻土区,被称为全球变化的“驱动机”和“放大器”。过去50年青藏高原变暖趋势明显,导致多年冻土发生显著退化,进而严重影响到区域水文、生态乃至全球气候系统。近30年高原变暖速率显著增加,且冬季变暖速率快于夏季变暖。这就引发了一个重要的科学问题,即冬季变暖如何影响整个高原多年冻土的变化。然而,迄今为止,尚未有研究评估多年冻土对冬季变暖的响应。

针对上述科学问题,我们以数值实验为手段,首次研究了青藏高原冬季变暖对多年冻土的影响,结果表明:

  • 1980−2009年,青藏高原冬季气温以0.66 °C/10a的速度升高,是夏季增温0.27 °C/10a的两倍多。在2000s,夏季变暖有所减缓而冬季变暖不断增强。
  • 多年冻土的活动层厚度主要受夏季变暖的影响,而季节性冻土的最大冻结深度主要受冬季变暖的影响。即使气候持续变暖,多年冻土的活动层厚度却呈轻微下降趋势,为0.07 m/10a。虽然多年冻土的面积总体上保持相对稳定,但过去30年,多年冻土的年平均低温以0.13 °C/10a的速度升高。
  • 2000年以前,夏季变暖主导着多年冻土热状况的变化,之后,冬季变暖对多年冻土热状况的影响逐渐增大并超过了夏季变暖,冬季变暖加剧了多年冻土的热退化。由于2000年以来冬季快速变暖,青藏高原北部羌塘高原的高寒连续多年冻土发生了显著的区域性变暖。这是先前研究从未报道过的一个新的发现。

该研究通过假设数值实验首次研究了冬季变暖对多年冻土变化的影响,为理解青藏高原多年冻土对季节性变暖的响应提供了一个新的视角。

Abstract

Winter warming is fast than summer warming on the Qinghai‐Tibet Plateau (QTP). However, no assessment of winter warming effects on permafrost has been attempted. Here we conducted hypothetical control experiments and used the Noah land surface model to evaluate the impacts of winter warming on the QTP permafrost. The results show that air temperature in winter (November–April) was increasing at a rate of 0.66 °C/decade during 1980s−2000s, over double that in summer (May–October). The mean annual ground temperature of permafrost increased by 0.13 °C/decade. The summer warming dominated the variations in thermal regime of permafrost before 2000. After that, the influence of winter warming on permafrost thermal regime has gradually grown and exceeded that of summer warming. Winter warming has amplified the thermal degradation of permafrost. Our findings reveal that alpine continuous permafrost on the northern QTP has experienced a prominent regional warming due to rapid winter warming since 2000.

Citation: Zhang G, Nan Z, Wu X, Ji H, Zhao S. The role of winter warming in permafrost change over the Qinghai-Tibet Plateau. Geophysical Research Letters. 2019, 46. DOI:10.1029/2019GL084292.

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