Ground surface deformation characteristics of different alpine-grassland types in the permafrost zones of Qinghai-Tibet Plateau

作为气候变化"指示器"的青藏高原多年冻土，近几十年来受到越来越多学者关注。但是已有冻土区地表形变的研究，多单纯针对地表抬升和沉降量进行分析，鲜有针对不同高寒草地类型进行深入挖掘的。在位于青藏高原多年冻土区腹地的五道梁地区，利用ASAR数据和SBAS-InSAR方法反演了区域内2005年4月到2010年7月的地表形变状况。结果显示研究区地表形变速率基本位于±8 mm/a之间。其中，变形率为正、地表呈现抬升的区域占57.70%，地表形变为负、地表沉降的区域占42.30%。此外，高寒草地整体表现地表下沉的现象，而且高寒草原的地表沉降现象明显强于高寒草甸地区。计算获得3种生态遥感指数后，分析地表形变与生态遥感指数的相关性，发现针对不同草地类型，其地表形变的主导因子存在差异。高寒草甸的地表形变有可能更多的受限于温度变化，而高寒草原的地表形变则可能更多的由水分条件所影响。以上研究说明青藏高原多年冻土区植被类型条件越好，地表沉降量越小。因此今后的相关研究需要对植被类型条件差的区域增加更多的关注，因为这些地区易发生地表沉降，导致其生态系统稳定性较差。;Global warming has received great attention from different research community, especially the warming changes of permafrost in Qinghai-Tibet Plateau (QTP) is one of the core study topics of global terrestrial ecosystems in recent decades. Because shifts of permafrost affect water circulation, biological diversity, geophysical process and carbon storage in this fragile plateau region. Permafrost, which has remained two or more years at or below the freezing point, has been considered as an indicator of climate changes. Existing studies lack detailed description of the response of permafrost change to different vegetation types, just focus on the analysis uplift and subsidence of ground surface. In this paper, ground surface deformation of permafrost in different type of alpine grasslands will be explored. The study area is located in Wudaoliang, which is one hinterland zone of QTP permafrost zone. The ground surface deformation of this region is inverted by advanced synthetic aperture radar (ASAR) data and the small baseline synthetic aperture radar interferometry (SBAS-InSAR) method. There were 24 ENVISAT ASAR images acquired from April 7th, 2005 to July 15th, 2010. They were employed to calculated the ground surface deformation, and the results showed that deformation rates of ground surface are primarily between ±8 mm/a. The area of positive deformation rate accounts for 57.70%. In this region, ground surface is uplifted. Conversely, area of negative surface deformation occupies 42.30%, where is subsidence region. The results were demonstrated that SBAS-InSAR technique can provide a useful tool to monitoring the surface deformation of different alpine vegetation types in permafrost regions. Furthermore, the ground surface of alpine grassland is subsidence mainly. And the surface subsidence is large in alpine grassland, compared with alpine meadow. In this study, there were 3 types of remote sensing based ecological indexes (RSEI), including normalized differential green index (NDGI), normalized differential wet index (NDWI) and normalized differential land surface temperature index (NDLI) to research the relationship between ground surface deformation and environmental factors. It is concluded that in QTP the deformation limited factors of alpine grasslands with different vegetation types were different. The surface deformation of alpine meadow might be limited by temperature change, while deformation of alpine grassland might be affected by water conditions. It indicates that region with abundant vegetation is not vulnerable to the ground surface subsidence, in permafrost areas of the QTP. Therefore, future studies should focus on the areas with scarce vegetation. Because there will be taken place land subsidence in these areas, and then the ecological stability in this area will be fragile.