Increasing risk of glacial lake outburst flood in Sikkim, Eastern Himalaya under climate warming

Abstract

The increasing risk of Glacial Lake Outburst Floods (GLOFs) in the Eastern Himalaya is exacerbated by climate change-driven glacial ice mass loss, slowdown, and increasing infrastructure projects in the high-altitude regions. To quantify the current risk of potential future disasters we update the inventory of glacial lakes in Sikkim Himalaya, identify the most potentially dangerous glacial lakes (PDGL) and model their peak discharge in different scenarios. The updated glacial lake inventory includes 232 glacial lakes (of >0.01 km²) covering a cumulative area of 22.23 ± 0.10 km². Our GLOF susceptibility mapping of all moraine-dammed glacial lakes using an Analytic Hierarchy Process (AHP) reveals one lake as very high risk, eight as high risk, 22 as medium risk, 56 as low risk, and 18 as very low risk. Further, we apply dam break flood simulations for the seven most dangerous lakes. Results reveal highest peak discharges of 9504 m³ s⁻¹ and 8421 m³ s⁻¹ in extreme case scenarios from the Khanchung and South Lhonak lakes, respectively. The lowest peak discharge of 622 m³ s⁻¹ is estimated in a normal outburst event for Yongdi lake, with every scenario at least 447 m³ s⁻¹ discharge is reaching to Chungthang town. We find that more than 10,000 people face direct threat of GLOF with potential large-scale infrastructure damage (∼1900 settlement, 5 bridges and 2 hydropower plants). The updated glacial lake dataset, GLOF susceptibility mapping, and modeling results demonstrate the urgent need to install an early warning system and control breaching of highly dangerous lakes.