Accelerating glacier mass loss in Bhilangana Valley since the 1970s

Himalayan glaciers are important for freshwater supply, hydropower and ecosystem services and require continuous monitoring due to climate warming. Garhwal Himalayan glaciers are experiencing mass loss, but long-term studies on mass balance remain limited for Bhilangana Valley glaciers. This valley is an important sub-basin of the Bhagirathi River that contributes meltwater to the Tehri Reservoir and supports downstream agriculture and populations. Therefore, we assess elevation changes (Δh/Δt), mass balance, frontal retreat and area changes for six Bhilangana Valley glaciers (Khatling, Phating, Dudhganga, Ratangariyan, Jogin and an unnamed glacier) using satellite imagery and digital elevation models (DEMs) from 1973 to 2025. Analyses revealed glacier separation, accelerated retreat, thinning and mass loss, with rates expanding up-glacier toward accumulation zones. The unnamed and Khatling glaciers exhibited approximately four to fivefold increases in mass loss during 2014–2025 compared with 1973–2000, while Dudhganga and Jogin could not be evaluated for 1973–2000 due to DEM voids. Khatling retreated ~5.33 ± 0.04 km, separating from Phating around 2000. The unnamed glacier receded ~0.76 ± 0.04 km, forming a potentially hazardous proglacial lake (~0.36 km2 by 2024). This study provides the first comprehensive long-term geodetic mass balance assessment that reveals heterogeneous glacier responses to warming, highlighting the need for hazard monitoring and sustainable water management.