| Glacier is considered as natural solid reservoir. The Tibetan Plateau holds 29.9% glacier volume of Asia and 81.6% of China, which is known as "Asian Water Towers". It plays an important role in freshwater supply of densely populated South and East Asia. Under the influence of global warming, most of the glaciers have, in recent decades, been retreating and losing ice rapidly. Glacier shrinkage not only increase the runoff, contribute to sea level rise, but also affect the regional water resources and ecological security directly.Quantitative assessment of thickness and volume change is one of the important parts of evaluating the potential impact of glacial shrinkage. However, the current studies of alpine glacier thickness still have many inadequacies, the method is scarce and the accuracy improvement is pressing. The most commonly used method is to comparing multi-temporal Digital Elevation Models (DEM), which lacking of high-precision observational method within a short period. Meanwhile, the thickness change with short-timescale is of great significance for the analysis of glacial retreat.Therefore, based on GPS measurement, Ground Penetrating Radar (GPR), remote sensing images and in situ decimeter-accuracy differential global position system measurements, the changes of glacier thickness, area, terminus and ice volume are investigated. In addition, we analysis the terrain-section characteristics and the glacier response to climate change. Results are summarized as followings:(1) During the study period, four typical glaciers are basically in the trend of shrinkage. Glacier thickness shrinkage is correlated reciprocally with the elevation. At the same elevation range, Gurenhekou glacier and Kangwure glacier depth loss faster than two others. And according to the temperature rise, the ablation area of glacier is expanding, even the elevation exceed 6000 m, Naimona’nyi glacier thickness still retreated. The glacier thinning rate generally decreases from the Himalayas to the continental interior, and show an approximate accelerating retreat as the time approaches.(2) GPR measurement results show that the glacial trough valleys is developed in Naimona’nyi glacier and Qiangtang No.1 glacier, Gurenhekou glacier followed. However, it’s not well developed in Kangwure glacier because of different terrain conditions. Due to the ice differential erosion, all the glaciers show step fluctuation characteristics on the longitudinal profile except of Naimona’nyi glacier.(3) The reduce in glacier area and length is respectively 0.82 km2 (0.52%/a) and 202.8 m (20.3m/a) for the Naimona’nyi glacier from 2003 to 2013,1.23 km2 (1.03%/a) and 372.8 m (9.3 m/a) for the Kangwure glacier from 1974 to 2014,0.29 km2 (3%/a) and 101.7m (14.5 m/a) for the Gurenhekou glacier from 2007 to 2014,0.32 km2 (0.28%/a) and 207.3 m (4.7 m/a) for the Qiangtang No.l glacier from 1970 to 2014. The Sub-continental type glacier area retreat dramatically than Extreme continental type glacier.(4) In the long-timescale, Kangwure glacier volume (1974-2014), Qiangtang No.1 glacier volume (1970-2014) has decreased by 52.75% and 17.54% respectively. In the short-timescale, Gerenhekou glacier volume (2007-2014), Naimona’nyi glacier volume (2003-2013) has decreased by 28.71% and 7.53%. According to linear prediction model, the thickness of kangwure and Qiangtang No.1 glacier will be reduced by more than thirty percent by 2020 and more than half by 2050. The area shrinkage will become much stronger. Following the current speed, the area of kangwure glacier will be reduced nearly 80% and Gurenhekou glacier will disappear completely in the next 35 years. The forecast retreat percent of Naimona’nyi glacier in the future is relatively small.(5) Glacier area and terminus retreat rate have a good consistency, but different from mean thinning rate. Except of Gurenhekou glacier, glacier horizontal and vertical change rate show an obviously inverse relationship in the other three glaciers, the larger mean thinning rate, the slower area and terminus retreat rate. Although Gurenhekou glacier doesn’t reflect this relationship in the short-timescale, it is reflected in the long-timescale. The glacier three-dimension changes are shown asymmetrically in the proportion, and the proportion of thickness clearly loss much more than area and length at the same period. Also we found a recent annual change proportion is greater than the forward from two glaciers with long term data record.(6) The retreat of typical glaciers in the Tibetan Plateau are mainly result from the temperature rising, especially the summer temperature. Though the precipitation increased in some area, the glacial accumulation cannot compensate the glacier ablation caused by climate warming. Naimona’nyi glacier retreat is attributed to the rapid temperature rise and precipitation decrease. Moreover, the glacier size and topography are also the important factors, larger glaciers retreat relatively slow than smaller glacier size. |
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