Reconstructing glacier retreat since the Little Ice Age in SE Tibet by glacier mapping and equilibrium line altitude calculation
Reconstructing glacier retreat since the Little Ice Age in SE Tibet by glacier mapping and equilibrium line altitude calculation
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DOI：
10.1016/j.geomorph.2014.03.018
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发表时间：
2014-06
期刊：
影响因子：
3.9
通讯作者：
D. Loibl;F. Lehmkuhl;Jussi Grießinger
中科院分区：
文献类型：
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作者：
D. Loibl;F. Lehmkuhl;Jussi Grießinger
西藏东南部念青唐古拉山脉东部的温带冰川对气候变化非常敏感，因此对研究全新世晚期高亚洲季风气候变化具有重要意义。然而，由于该地区地处偏远，经验数据稀缺，以及云和积雪对遥感工作构成的挑战，有关该地区冰川动态和变化的知识仍然非常有限。在这项研究中，我们采用了遥感方法，其中1964年冰川绘制从Landsat ETM+场景，随后参数化DEM支持的测量。地貌证据，即，利用冰川边缘线和侧额冰碛等资料，定量研究了冰川的形态特征和小冰期（LIA）以来冰川最大推进期的变化。对冰川长度变化的统计分析显示，平均退缩约27%，较小的冰川有更强的退缩趋势。不同方法计算平衡线高度（ELAs）的评价表明，一个优化的脚趾到山脊高度的方法（TRAM）是更适合于设置与复杂的地形和缺乏质量平衡测量比其他方法。大量的冰川测量对于高质量的TRAM结果至关重要，必须特别注意不同的冰川特征。为了确定最合适的TRAM比值和测试计算的ELA的质量，遥感方法：对于每个被调查的冰川，在夏末Landsat场景中可见的瞬时雪线的高度从DEM测量，并与TRAM结果进行比较。内插ELA结果显示，东南-西北梯度范围从4400至5600米asl和平均ELA上升约136米，因为LIA。由于高空间分辨率的测量，ELA分布揭示了地形的影响下到流域尺度，特别是地形降雨和背风屏蔽。这些模式的解释表明，念青唐古拉山脉东部的影响，印度（ISM）和东亚夏季风（EASM）。然而，东亚夏季风并没有到达研究区的西部。结果表明，季风温带冰川对气候变化的高敏感性是由两个双重强迫驱动的，这两个强迫是由于冰川堆积和消融阶段的重合造成的。
Temperate glaciers in the eastern Nyainqêntanglha Range, southeastern Tibet, are highly sensitive to climate change and therefore of particular high interest for research on late Holocene changes of the monsoonal climate in High Asia. However, because of the remoteness of the area, the scarcity of empirical data, and the challenges to remote sensing work posed by cloud and snow cover, knowledge about the glacier dynamics and changes in this region is still very limited. In this study, we applied a remote sensing approach in which 1964 glaciers were mapped from a Landsat ETM+ scene and subsequently parameterized by DEM-supported measurements. Geomorphological evidence, i.e., trimlines and latero-frontal moraines, were used to obtain quantitative data on the glaciers' morphological characteristics and the changes since the Little Ice Age (LIA) maximum glacier advance. Statistical analysis of glacier length change revealed an average retreat of ~ 27% and a trend toward stronger retreat for smaller glaciers. An evaluation of different methods to calculate equilibrium line altitudes (ELAs) indicates that an optimized toe-to-ridge altitude method (TRAM) is more suitable than other methods in settings with complex topography and a lack of mass balance measurements. A large number of glacier measurements are crucial for high quality of TRAM results, and special attention has to be paid to different glacier characteristics. In order to determine the best-fitting TRAM ratio value and to test the quality of the calculated ELAs, a remote sensing approach was applied: for each investigated glacier, the altitudes of transient snowlines visible in the late summer Landsat scene were measured from the DEM and compared to TRAM results. The interpolated ELA results show a SE–NW gradient ranging from 4400 to 5600 m asl and an average ELA rise of ~ 136 m since the LIA. Because of the high spatial resolution of measurements, the ELA distribution reveals topographic effects down to the catchment scale, specifically orographic rainfall and leeward shielding. The interpretation of these patterns reveals that the eastern Nyainqêntanglha Range is influenced by both, the Indian (ISM) and East Asian summer monsoon (EASM). However, the EASM does not reach the western part of the study area. The results indicate that the monsoonal temperate glaciers' high sensitivity to climate change is driven by two double forcings owing to the coincidence of accumulation and ablation phases.