Glacier status during the period 1973-2014 in the Hunza Basin, Western Karakoram

Glacier changes in the Karakoram have shown a complex pattern since the recent decades with the coexistence of advancing, retreating, and stable glaciers, but the mechanisms driving these changes remain, for the most part, unclear. We examined the changes in glacier length, area, and elevation in the Hunza Basin of the upper Indus River region, western Karakoram, using CORONA remote sensing data, Landsat MSS/TM/OLI imagery, SRTM digital elevation model (DEM), and GLAS/ICESat altimeter data. We delineated 108 glaciers within the study area. The total area of these glaciers decreased 28.86 km2, or 1.36%, from 2115.48 km2 in 1973-2086.62 km2 in 2014. The most significant reduction in ice coverage occurred between 1992 and 1998, when glaciers retreated on average at a rate of −2.97 km2/yr (0.85% of the total coverage measured in the 1970s). In contrast, many glaciers advanced from 2008 to 2014 and glacial coverage increased by 0.19 ± 0.00 km2. In comparison to fast retreating glaciers in the Hindukush and the Trans-Himalayan regions, the glaciers in the Hunza Basin are relatively stable. The topographical characteristics and the size of the glaciers have direct impacts on glacial changes in the Hunza Basin. Specifically, significant changes occurred mainly below 5500 m above sea level, glaciers retreated more extensively on steep slopes than on gentle slopes, and small glaciers retreated relatively faster than large glaciers. The overall pattern of glacial retreat is related to the warming trend in summer temperature, whereas the relative stability of glaciers in the Hunza Basin, as well as their recent advance (2008-2014), is likely driven by increasing autumn and winter precipitation.