Zhangmu and Gyirong ports under the threat of glacial lake outburst flood

The Himalayas are prone to glacial lake outburst floods, which can pose a severe threat to downstream villages and infrastructure. The Zhangmu and Gyirong land treaty ports are located on the China-Nepal border in the central Himalayas. In recent years, the expansion of glacial lakes has increased the threat of these two port regions. This article describes the results of mapping the glacial lakes larger than 0.01 km² in the Zhangmu and Gyirong port regions and analyzes their change. It provides a comprehensive assessment of potentially dangerous glacial lakes and predicts the development of future glacial lakes. From 1988 to 2019, the glacial lakes in these port regions underwent "expansion", and moraine-dammed lakes show the most significant expansion trend. A total of eleven potentially dangerous glacial lakes are identified based on the assessment criteria and historical outburst events; most expanded by more than 150% from 1988 to 2019, with some by over 500%. The Cirenmaco, a moraine-dammed lake, is extremely prone to overtopping due to ice avalanches or the melting of dead ice in the dam. For other large lakes, such as the Jialongco, Gangxico and Galongco, ice avalanches may likely cause the lakes to burst besides self-destructive failure. The potential dangers of the Youmojianco glacial lakes, including lakes Nos. 9, 10 and 11, will increase in the future. In addition, the glacier-bed topography model predicts that 113 glacial lakes with a size larger than 0.01 km², a total area of 11.88 km² and a total volume of 6.37×10⁹ m³ will form in the study area by the end of the 21 century. Due to global warming, the glacial lakes in the Zhangmu and Gyirong port regions will continue to grow in the short term, and hence the risk of glacial lake outburst floods will increase.