Glacial lake outburst floods (GLOFs) pose significant risks in High Mountain Asia, particularly in transboundary Himalayan basins. This study aims to assess the threat from future glacial lakes alongside worst-case scenarios from existing lakes, focusing on two identified dangerous lakes, Galongco and Jialongco. The research compares the timing and magnitude of simulated worst-case outburst events from these lakes in the Tibetan town of Nyalam and downstream at the Nepal border. A future scenario involving an avalanche-triggered GLOF for a potential large new lake upstream of Nyalam was also assessed. Results indicate that large rock and/or ice avalanches could produce GLOF discharges at the Nepal border that are over 15 times larger than previously observed or anticipated based on gradual breach simulations. Warning times in Nyalam would be only 5–11 minutes and 30 minutes at the border. Recent measures to lower the water level at Jialongco would have minimal impact on downstream effects from a large-magnitude GLOF, especially in Nyalam, where significant infrastructure development has occurred within high-intensity flood zones. The findings suggest a need for a comprehensive disaster risk management approach that combines early warning systems, effective land use zoning, and local response capacity building to address current GLOF risks and prepare for worst-case scenarios under a warming climate.
The retreat of glaciers in the Himalayas has accelerated due to global warming, leading to the rapid expansion and formation of glacial lakes, which have significant implications for water resources and hazards. GLOFs can cause extensive damage downstream, with a recorded frequency of 1.3 GLOFs per year since the 1980s in the Himalayas. The transboundary nature of these lakes complicates early warning and risk reduction strategies in politically sensitive areas.
Lakes can form in various locations relative to glaciers, with moraine-dammed lakes being particularly hazardous. Displacement waves from large impacts of ice or rock have been the primary cause of moraine dam failures, predominantly occurring in warmer months. At least 17 GLOF disasters have been documented in Tibet since 1935, underscoring the urgent need for risk reduction measures as population and infrastructure grow in the region.
While no clear trend in GLOF activity has been observed in recent decades, the ongoing expansion of lakes towards unstable mountain flanks is expected to create new hazards. Studies have indicated a potential increase in GLOF frequency and magnitude in future scenarios, highlighting the need for anticipatory hazard and risk modeling. This study aims to provide a systematic assessment of worst-case outburst scenarios from existing and potential future lakes, contributing to disaster risk management in a transboundary context.
The analysis focuses on the lower Poiqu river basin, assessing potential GLOF impacts in Nyalam and downstream to the Nepal border at Zhangmu. The study area spans a significant elevation range, with climatic data indicating specific temperature and precipitation patterns. The Poiqu basin is recognized as a hotspot for transboundary GLOF risks, with multiple major GLOF events reported in the past century. The findings emphasize the importance of timely risk reduction measures and the need for comprehensive assessments of both current and future threats.