Hazard assessment of a pair of glacial lakes in Nepal Himalaya: unfolding combined outbursts of Upper and Lower Barun

Abstract

Due to climate change, the future Glacial Lake Outburst Flood (GLOF) risk is more likely in the Himalayas. Despite several GLOF studies, little attention has been given to the combined surge that can result from a pair of upstream-downstream glacial lakes. We chose Upper and Lower Barun glacial lakes as a pilot study due to the region’s increasing population and hydropower investments and the possible outbursts of upper-lower glacial lakes. This study mainly considered four scenarios (100 and 50% breach combination of upper-lower lakes), using a two-dimensional dam break model and inundation propagation. Based on our observations, the glaciers in the study area shrank by 33 km², and the two glacial lakes expanded by 2.06 km² between 1976 and 2020. The modeling result suggests that the single flood triggered by Upper Barun cannot travel beyond 50 km; however, the combined flow from the lakes could reach over 85 km. Our results illustrate that at least 60 buildings, motorable bridges, and infrastructures of Arun hydropower along the river course have high damage potential. The study insights can be helpful for effectively planning and formulating various disaster risk reduction initiatives to mitigate the likely effects of glacial lake(s) outbursts.

Keywords:

• GLOF
• dam break
• combined
• hydrodynamic
• Nepal Himalaya

Acknowledgments

MRG acknowledges the ‘ANSO Scholarship for Young Talents’ for his postgraduate study, and NK acknowledges CAS-TWAS Scholarship for his Ph.D. study.

Code and model availability

The hydrometeorological data were obtained from the Department of Hydrology and Meteorology (DHM). All other datasets and models used in this study are open-source and freely available from the sources cited in the text.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research was funded by the Second Tibetan Plateau Scientific Expedition and Research Program [2019QZKK0902] and the National Natural Science Foundation of China [41790434].