Multi-breach GLOF hazard and exposure analysis of Birendra Lake in the Manaslu Region of Nepal

Recent climate change has resulted in the shrinkage of glaciers and the expansion of the glacial lakes in the Himalayas, thereby increasing the risk of Glacial Lake Outburst Floods (GLOFs). GLOFs from moraine-dammed glacial lakes are often liable to many casualties and colossal devastation of the downstream settlements and infrastructure. Nevertheless, these hazards have been largely overlooked in the Manaslu Region of the Nepal Himalaya, which witnessed a small GLOF from Birendra glacial lake on April 21, 2024, due to a snow-ice avalanche. Here, we used an integrated approach to study the evolution of Birendra Lake and its parent glaciers. We then conducted its GLOF hazard assessment in multi-scenarios by employing remote sensing, geographic information system (GIS), and hydrodynamic model. The results show that the parent glacier shrunk from 25.842 ± 1.21 to 21.56 ± 1.26 km 2 between 1988 and 2024, and subsequently, the glacial lake expanded from 0.09 ± 0.02 km 2 to 0.22 ± 0.03 km 2 . Three anticipated multi-scenario GLOF simulations were run using a two-dimensional (2D) dam break model, and the resulting flow was routed approximately 45 km downstream from the dam site. The results showed that the peak dam break flow ranges between 909 and 3,768 m 3 /s in 10, 15, and 20 m breach height scenarios, and approximately 110 buildings on the downstream side will be submerged in the worst scenario. This study provides insights into the possible consequences of GLOFs in the Himalayan headwaters and contributes to planning and formulating disaster risk reduction and mitigation programs, particularly in the Manaslu region.