Expansion of Lirung Glacial Lake in the Langtang Basin, Nepal: Implications for mountain water sustainability and GLOF risks

Abstract

Glaciers are natural reservoirs of freshwater that cater to the millions of people in a mountainous country like Nepal. However, these freshwater sources are retreating at an alarming rate, altering the downstream flow. Furthermore, this has led to an increase in glacial lake areas and their number, which may eventually be at risk of Glacial Lake Outburst Floods (GLOFs).  This study focuses on the expansion of Lirung Glacial Lake in the Langtang Basin from 2010 to 2024, utilizing multi-temporal satellite imagery from Landsat and Sentinel. The Normalized Difference Water Index (NDWI) was applied to delineate lake boundaries, which were then analyzed in conjunction with climate data from the basin. The result shows that over 14 years, the lake’s area has increased at an approximate rate of 0.0035 km² per year from 1.55 km² in 2010 to 6.36 km² in 2024,  which is an increase of 60.8%, indicating significant glacier retreat. The mean annual temperature in the basin is increasing, and precipitation is slightly declining, which are conditions favorable for accelerated glacier mass loss. These findings underscore the heightened risk of GLOFs, with potential impacts on downstream communities and critical infrastructure, including Nepal’s only glacial lake-fed micro-hydropower plant. The study highlights the urgent need for continuous monitoring, community-based early warning systems, and adaptive water resource management to safeguard mountain communities and their livelihoods in the face of climate change.