Plateau Lake and Cyrosphere Dynamic Analyzing in 1990s and 2000s for Tibetan Plateau
Li, Gang1; Lin, Hui1; Chen, Fulong2
1Institute of Space and Earth Information Science, The Chinese University of Hong Kong, HONG KONG; 2he Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, CHINA

As the third pole of the world, plateau lake and cyrosphere dynamic of Tibetan Plateau is the indicator for global changing. In the last two decades, plateau lakes presented more activity than before in Tibet. For interior drainage area occupies about 50.8% of Tibet, dynamic of those closed lakes could be regards as a proxy of cryosphere changing. We therefore selected Silin Co, Nam Co, Zari Namco, Tangra YumCo, Yamzhog Yumco and Bam Co, whose basin areas are large enough hence with vast permafrost and/or glacier distribution and/or showed significant changing, as typical lakes. To derive area time series, we acquired cloud free Landsat TM/ETM+ images for each lake. Since its bank terrain could also easily affect lake area dynamic, we also acquired satellite altimeter data like ICESAT, Envisat/RA2 to monitor lake height changing to void such influence. In additional, for satellite altimeter can only survey footprint height therefore some small lake could be missed, we additionally obtained Envisat/ASAR, ERS SAR images for analyzing ground subsidence or upwards of lakes adjacent area caused by mass loading with persistent scatterer intereferometry. Silin Co, the largest lake in TP with a basin area of 45530 KM2 and vast permafrost distribution presented 8m level increasing in 2000s. Nam Co, the second largest lake in TP, with a similar area, but 1/5 basin area and much less permafrost distribution with respect to Silin Co, presented only 2m upwards. In addition, some small lakes, such as Bam Co, also presented significant increasing by analyzing area changing associate with by taking water loading introduced ground subsidence as a proxy of lake level increasing. We also analyzed glacier and permafrost distribution in each basin. Bam Co Lake, mainly supplied by surface runoff and without any glacier distribution in its basin, presented 30% area increasing and around 2mm/a ground subsidence by water loading while Nam Co failed to cause any obvious ground subsidence. Considering Bam Co Basin is adjacent to Nam Co Basin, they could share similar metamorphic condition. Since Nam Co is mainly supplied by Nyainq"ntanglha glacier melting, and precipitation increasing, evaporation decreasing cannot fully explain lake dynamic in the past two decades, we therefore conclude that permafrost degradation is the main reason for tremendous lake dynamic in Tibetan Plateau in the 1990s and 2000s. Tibetan Plateau distributes the most vast seasonal permafrost, increasing of its active layer is not only a symbol for global warming, but also compromising the safety of large man-made linear features such as Qinghai-Tibet Railway.