Characteristics and changes of the Himalayas glacial area in China during 1990–2015

In recent decades, the continuously changed glaciers in the Himalayas not only affected process of atmospheric flow and water cycle in the plateau but also increased the frequency of secondary disasters, such as ice collapse and outburst floods. Therefore, the monitoring of Himalayas glacial change is of great significance in the aspects of climate change and disaster prevention and reduction. The Himalayas glacier outlines in China were extracted by ratio threshold and visual interpretation based on the Landsat TM/ETM+/OLI data and glacier catalogue data. Based on the ASTER GDEM data, the distribution and change characteristics at different altitudes were studied, and the surface moraine was identified to study the influence of glacial area variations. In addition, Glaciers were divided into marine and continental glaciers in this study, and the distribution and changes of the two types of glaciers were analyzed. Also, a comprehensive analysis of a long time series was performed. The results showed that: (1) From 1990 to 2015, the glaciers in the study area showed an overall trend of melting; the annual melting speed gradually accelerated from 0.48%/a to 0.75%/a. The total melting glacial area was 828.16 km 2 , and the melting rate of the glaciers in the western section was the highest, at 0.63%. (2) The total area of continental glaciers was larger than that of marine glaciers, and its reduction was relatively larger, too. (3) The average size of debris-covered glaciers was 10 times that of debris-free glaciers, but their rate of change (8.1%) was 1/2 of that of debris-free glaciers (17.8%). (4) The number of glaciers gradually decreased as the size of glaciers increased. The glaciers with grades of >50 km 2 , 0.5∼1 km 2 , and 1∼2 km 2 had large change rates, which were 20.1%, 19.1%, and 18.5%, respectively. In summary, the Himalayas glaciers in China were melting at an accelerated rate and their numbers were gradually decreasing from 1990 to 2015. The location, type, elevation, size and debris cover of a glacier are all important factors influencing glacier change. It has been found that the lower the elevation or the smaller the size of the glacier, the greater the likelihood of glacier ablation, and the debris can inhibit the melting of glaciers to a certain extent.