Early 21st century accelerated glacier shrinkage and associated climatic drivers in Bhaga basin, north-western Himalaya

This study investigates the glacier changes in the Bhaga basin, western Himalaya during the last five decades based on various satellite imagery: Corona KH4 (1971), Landsat 7 Enhanced Thematic Mapper Plus (ETM+; 2000), Linear Imaging Self-Scanning Sensor (LISS IV; 2013), Sentinel 2 (2016 and 2018). We compare glacier changes on spatial and temporal scales and their dependency on local topographic settings (elevation, slope, aspect, debris cover, presence of glacial lakes) and climatic fluctuations. Long-term (1900-present) reanalysis climatic datasets were evaluated to monitor the temperature and precipitation trend of the region. Glacier mapping from 2013 (LISS IV) images yielded 306 glaciers (>0.2 km²) with a total area of 360.3 ± 4.0 km², of which 55.7 ± 0.6 km² was covered by debris. Glaciers in the Bhaga basin lost -7.9 ± 1.5% (-0.17% yr¯¹) of ice during 1971-2018 with a significant heterogeneous rate within tributary watersheds. The number of analyzed glaciers increased by nine due to fragmentations. In recent decades (2000-18), the deglaciation rate has increased significantly (-0.25% yr¯¹) compared to previous decades (1971-2000; -0.12% yr¯¹). The retreat rate has been observed to be much lower than previously reported. Heterogeneous ice loss was mostly controlled by the size, altitudinal range, orientation, and debris cover. Analysis and inter-comparison of multiple gridded climatic data during the last century shows a drastic change in climatic trends around 2000 in western Himalaya. Asian Precipitation-Highly Resolved Observational Data Integration Towards Evaluation (APHRODITE) data reveals an increasing trend in temperature (0.019° C yr¯¹) and a significant decreasing trend in precipitation (-1.969 mm yr¯¹) after 1990. The observed glacier change in the Bhaga basin is in similarity to the observed climatic trend for the western Himalaya.