Glacier changes on the Tibetan Plateau since the 1970s

Abstract:

Glacier area on the Tibetan Plateau (TP hereafter) and its change were studied in different drainage basins by time series of Landsat satellite images since the 1970s. High resolution of various optical images of good quality, with minimal cloud and snow cover, were selected for glacier extraction on TP. There were 240 scenes of Landsat MSS with 60 m spatial resolution in 1970s. There are 150 scenes of Landsat7 ETM+ images (spatial resolution: 30m) were selected for periods of 1999-2002. 148 scenes of L1T were selected from the Operational Land Imager (OLI) of Landsat 8 with 30-m multi-spectral spatial resolutions. All satellite data were mosaicked to represent three periods, i.e. 1970s, 2000s, 2013/2014. The majority date in each period was adopted as the mosaic image date: i.e. 1976, 2001 and 2013. Glacier outlines were digitized manually based on the three mosaics by RGB: 432, with reference of SRTM DEM v4.1 and Google Earth imagery. The adjacent glaciers were regarded as continuous ice body, or glacier complexes that have not been subdivided into single glaciers. The debris-covered ice was not involved in the study. Overall glacier area uncertainty was evaluated at three study sites here where our previous regional studies available by different methods, which includes the Mt. Qomolangma, Mt. Naimona’Nyi, Mt. Geladandong. All evaluations were carried out in the same periods. The largest difference between the data sets was within ~±8%. In 1976, glaciers cover 1.7% of the TP study area as a whole, however, 56% of all the studied glacier area locates in interior drainage basins (IB hereafter). Glacier area on the TP has decreased at an accelerating rate over the last several decades, from 44,366 ± 4329 km² in 1976 to 42,210 ± 2469 km² in 2001 (area change was -2,156 km² by -4.86%, or -0.19% a^-1), and further decreased to 41,137 ± 2269 km² in 2013 (area change was -1,073 km² by -2.54%, or -0.21% a^-1).

ICESat/GLAS data from 2003–2009 were used to calculate glacier surface elevation and its mass changes over TP. Glacier surface elevation changes were calculated, and glacier mass changes evaluated, for each glacier in the Second Chinese Glacier Inventory. For external catchments on TP, glacier mass change totalled by -16.13 ± 5.8 Gt a^-1 during 2003-2009. For internal basins on TP, glacier mass change totalled by -4.32 ± 1.2 Gt a^-1 during 2003-2009.