Glacier Retreat and Lake Outburst Floods in the Central Himalayan Region from 2000 to 2022

Recent research on the Himalayan cryosphere has increasingly been focused on climate uncertainty and regional variations, considering features such as glacier recession, lake expansion, outburst floods, and regional hazards. The Bhilangana river basin, located in the central Himalayas, is predominantly characterized by increased elevation-dependent warming and declining seasonal precipitation. Our study shows that high-elevation temperature increased from 2000 to 2022 (0.05 °C/year, p = < 0.05), which resulted in rapid frontal glacier retreat and expansion of glacier lakes. In this study, we used the Google Earth Engine platform to process satellite, reanalysis, and observational data records with descriptive and nonparametric statistical methods. Most of the debris-covered glaciers in this valley exhibited a significant rate of retreat in the last two decades (averaging 31 m per year), although the debris-free Masar glacier retreated even faster (49 m per year). In all, 13 glacier lakes were demarcated and intensively investigated at multi-temporal scales together with variations in area, volume, depth, and discharge at different geomorphologic locations. Maximum changes were detected in the land-terminated lake, which exhibited a significant increase in area (13,398 to 360,878 m2), volume (75,406 to 8,099,363 m3), depth (5.6 to 22.4 m), and discharge (13.3 to 304.6 m/sec) and is considered susceptible to a future flood event. In addition, unsteady flow estimation modeling was employed to describe peak discharge, depth, and velocity associated with regional flood extent over four distinctive simulation scenarios. Maximum peak discharge during the lake outburst is predicted to exceed 4500 m3/sec along with increased maximum water depth in the lower plains (44.2 m) and significantly elevated velocity (> 20 m/sec). Quantification of the regional hazard reveals potentially severe downstream challenges for low-to-medium-scale hydropower stations, local settlements, and road and railway bridges near Devling and Ghuttu villages.