Variations in glacier coverage in the Himalayas based on optical satellite data over the past 25 years

Because of the large area covered by glaciers, their extent and importance demands continuous assessment of the glaciers. In this study, we analysed the distribution and changes in glacier coverage throughout the Himalayas from 1990 to 2015. The results showed that 12,211 glaciers were identified in the whole mountain range, covering an area of 23229.27 km2 in 1990. Over the past 25 years, the glacier area decreased by 10.99% (2553.10 km(2)) with an accelerated shrinkage in the period 2010-2015. There was a normal distribution between glacial area and elevation with maximum glacier area between 5400-5600 m. The glacier area decreased at all elevations, and the highest absolute ice loss occurred in 5200-5400 m. The total area of debris-free glaciers was larger than debris-covered glaciers, and in consequence, the annual shrinking rate was three times higher (15.56% versus 5.22%). The features of these two types of glaciers suggest moraine can inhibit glacial ablation. The debris over Himalayas is mainly distributed in gentle zones where elevations are in the range of 4400-5200 m. The ice coverage of the temperate glaciers is larger than that of continental glaciers with greater area loss but lower shrinkage rate (9.84%.versus 13.73%) in 1990-2015. These findings provide detailed glacier inventory data for the entire Himalayan region and updated information for the study of glaciers on a large scale.