Glacier change in the Poiqu River basin inferred from Landsat data from 1975 to 2010

The Poiqu River basin is a transboundary basin that is highly prone to glacial lake outburst floods. This basin is located in the middle of the Himalayas between China and Nepal. Fieldwork investigating nearby glaciers has indicated that glaciers in this region have ablated quickly in recent decades. A new glacier database for the Poiqu River basin was generated for the phases 1975, 2000, and 2010 using automatic classification and manual visual interpretation based on long time series Landsat data. In 2010, the Poiqu River basin had 124 glaciers with a total area of 203.4 ± 5.3 km2. Eleven glaciers have debris-covered tongues, with the debris covering a total area of 51.0 ± 1.5 km2. During the period of 1975–2000, the area change rates of all glaciers in the basin, clean ice and debris-covered parts were −0.45%/y, −0.71%/y and 0.96%/y, respectively. From 2000 to 2010, these area change rates were −0.82%/y, −1.24%/y and 0.73%/y, respectively. The number of glaciers and area change of clean ice within various size classes indicate that the large glaciers shrink into small glaciers and smaller glaciers retreated faster. The mean size of the glaciers in this basin is within the size class 1.0–5.0 km2. The area change rate for 1.0–5.0 km2 glaciers was similar to that of all glaciers in the Poiqu River basin. The altitude of the Region with the Fastest Change (RFC) uplifted from 5200 m to 5500 m, and the area change rate of glaciers in the RFC accelerated from −0.17 km2/y to −0.21 km2/y between the two periods, 1975 to 2000 and 2000 to 2010. Aspect analysis indicates that for a long time period, glaciers with southward aspects (including south, east, southeast and southwest) in the Poiqu River basin retreated faster than glaciers with northward aspects (including west, north, northeast and northwest). At the decade-scale, changes in areas of glaciers were more influenced by composition than aspect. Additionally, the retreat rate of the glaciers in the Poiqu River is in a state of accelerating ablation since 2000, despite elevation and aspect.