Changes in the ablation zones of glaciers in the western Himalaya and the Karakoram between 1972 and 2015

Observed estimates of changes in the Himalayan and Karakoram glaciers remain ambiguous because of limited knowledge regarding complex glacier behaviour, low quality of remote sensing data, and sparse ground-based monitoring. Remote sensing has indicated anomalous behaviour of glaciers in the Karakoram during the past two decades, attracting scientists' attention to the region. In this context, this study has made detailed estimates of changes in thickness and area of two glaciers (the Sachen in the western Himalaya and the Burche in the Karakoram) to facilitate understanding of recent glacier changes and their potential impacts on water resources. This study used several datasets, including Landsat, the Shuttle Radar Topographic Mission (SRTM), the Ice, Cloud and Land Elevation Satellite (ICESat), and differential Global Positioning System (dGPS) in-situ measurements, from the period 1972 through 2015. The extent of debris cover increased significantly between 1972 and 2014, while the total glacierized area decreased slightly. Further, our study estimated thickness changes after removing recognizable biases and seasonal variations, computed through comparisons of ICESat data with dGPS. A thinning trend occurred between 2000 and 2015, suggesting that the glaciers in the western part of the Karakoram and Himalaya regions have not recently gained mass. This study also found non-uniform variations within different zones of the glaciers. Avalanches have fed most of the Karakoram glaciers, providing spatially heterogeneous thickness changes. The frequency of observations, data quality, acquisition time, and local weather affect our observations of temporal changes. Careful assessment of regularly acquired remote-sensing and ground-based observations should reduce uncertainty regarding estimates of glacier changes for management of water resources and associated hazards.