Accelerated Glacier Area Loss and Extinction of Small Glaciers in the Bhutanese Himalaya over the Past Five Decades

Glacier inventories are critical for monitoring glacier response to climate change, providing constraints for glacier modeling studies and for assessing the impacts of glacier retreat on ecosystems and human societies. In the Bhutanese Himalaya, an up-to-date glacier inventory and a systematic analysis of decadal-scale glacier changes is lacking. Here, we present three glacier inventories (1976, 1998, and 2024) for this region. Manual mapping of glacier outlines from multi-source satellite imagery and the Copernicus digital elevation model (DEM) are used to derive a glacier inventory with associated topographic attributes. We found that 1871 glaciers existed in this region in 1976, covering an area of 2297.07 ± 117.15 km2. By 1998 this number had reduced to 1803 glaciers, covering 2106.99 ± 90.60 km2. In 2024, only 1697 glaciers remained, covering 1584.18 ± 36.37 km2. A total of 89 (1976–1998) and 435 (1998–2024) glaciers became extinct in the Bhutanese Himalaya during these two time periods, and glacier area decrease accelerated from ~0.38% yr−1 to ~0.95% yr−1. Lake-terminating glaciers retreated almost three times faster (~32.2 m yr−1) than land-terminating (~10.4 m yr−1) glaciers during the observation period. Debris-covered glacier area increased from 112.79 ± 11.50 km2 in 1976 to 128.89 ± 10.50 km2 in 2024. Glaciers on the South Bhutanese Himalaya (draining into Bhutan) experienced faster glacier retreat than the glaciers of the North Bhutanese Himalaya (draining into the Tibetan Autonomous Region). ERA5-Land reanalysis data show that summer decadal average temperature in this region increased by 0.003 °C yr−1 between 1976 and 1998 and 0.020 °C yr−1 between 1998 and 2024, with the increase in warming rate coinciding with accelerated glacier retreat after 1998. Our updated glacier inventories will be useful for assessments of global sea level change, mountain hazards, and water resources.