Integrating Field Observations, Remote Sensing and Modelling for the Assessment of Bhilangana Lake, Central Himalaya, India

Glaciers worldwide, including those in the Himalaya, are retreating under climate change, often leading to the formation and expansion of glacial lakes and an increased risk of Glacial Lake Outburst Floods (GLOFs). This study examines the evolution of the proglacial Bhilangana Lake (similar to 0.37 km(2); similar to 4750 m asl) and the associated glacier changes, including thinning and retreat, between 1968 and 2025 using satellite imagery, field measurements and hydrodynamic modelling. Results show lake expansion from similar to 0.12 km(2) in 2001 to similar to 0.37 km(2) in 2025, with an estimated volume of similar to 10.7 x 10(6) m(3), indicating exponential growth over time. A potential GLOF could release peak discharge of 3645 m(3)/s, with average flow velocity similar to 12 m/s, inundating similar to 6.8 km(2) and threatening hydropower projects, settlements and infrastructure downstream. Rising mean, maximum and minimum air temperatures at rates of 0.028, 0.052 and 0.05 degrees C/year, respectively, are identified as the primary drivers of lake expansion and accelerated melt, particularly in July-August. The zero-degree isotherm is shifting to higher elevations, and bias-corrected ERA5 data show good agreement at such altitudes, making it reliable for climate change analysis. Several over-deepening sites were also mapped as potential future lakes, with CMIP6 projections (similar to 0.8 degrees C/decade) indicating substantial glacial and hydrological changes, further elevating GLOF risk by the century's end.