Monitoring and assessment of glaciers and glacial lakes: climate change impact on the Mago Chu Basin, Eastern Himalayas

Glaciers and glacial lakes are susceptible to variations in climate and are global indicators of climate change. However, changes in glaciers and glacial lakes are rarely documented in the Eastern Himalayan region, especially from Bhutan and Arunachal Himalaya. This study attempts to bridge the knowledge gap on depletion of glaciers and glacial lake changes in the Eastern Himalayas by concentrating on the Mago Chu basin. Spatio-temporal changes in the glaciers and lakes extent and number in 1988 and 2018 are derived from Landsat TM and Sentinel-2 satellite imageries and major climatic drivers of change (temperature and precipitation) are analyzed from ERA5 reanalysis data. The number of glaciers was reduced from 92 to 86 during 1988–2018, whereas the glacial lakes increased from 134 to 195 in this period. The glacial area of 83.55 (± 6.2) km, which contributed to almost 10% of the total basin area in 1988, shrank to about 58.7 (± 1.6) km covering only 7% of the total basin area in 2018. Twenty smaller glaciers vanished, 12 fragmented, and 57 have retreated. Glacial lake area, on the other hand, increased from ~ 3.8 (± 1.2) km in 1988 to ~ 6.4 (± 0.0006) km in 2018, and 61 new lakes formed during this period. The new lakes are not proglacial but are glacier-fed, indicating retreat of glaciers. Climate data analysis shows increase in mean monthly temperature during the period in the study area supporting the changes observed in glaciers and lakes.