Glacial lake outburst flood hazard under current and future conditions: worst-case scenarios in a transboundary Himalayan basin

Abstract

Abstract. Glacial lake outburst floods (GLOFs) are a major concern throughout High Mountain Asia, where societal impacts can extend far downstream. This is particularly true for transboundary Himalayan basins, where risks are expected to further increase as new lakes develop. Given the need for anticipatory approaches to disaster risk reduction, this study aims to demonstrate how the threat from a future lake can be feasibly assessed alongside that of worst-case scenarios from current lakes, as well as how this information is relevant for disaster risk management. We have focused on two previously identified dangerous lakes (Galongco and Jialongco), comparing the timing and magnitude of simulated worst-case outburst events from these lakes both in the Tibetan town of Nyalam and downstream at the border with Nepal. In addition, a future scenario has been assessed, whereby an avalanche-triggered GLOF was simulated for a potential large new lake forming upstream of Nyalam. Results show that large (>20×106 m3) rock and/or ice avalanches could generate GLOF discharges at the border with Nepal that are more than 15 times larger than what has been observed previously or anticipated based on more gradual breach simulations. For all assessed lakes, warning times in Nyalam would be only 5–11 min and 30 min at the border. Recent remedial measures undertaken to lower the water level at Jialongco would have little influence on downstream impacts resulting from a very large-magnitude GLOF, particularly in Nyalam where there has been significant development of infrastructure directly within the high-intensity flood zone. Based on these findings, a comprehensive approach to disaster risk management is called for, combining early warning systems with effective land use zoning and programmes to build local response capacities. Such approaches would address the current drivers of GLOF risk in the basin while remaining robust in the face of worst-case, catastrophic outburst events that become more likely under a warming climate.

Modeling Potential Glacial Lake Outburst Flood Process Chains and Effects From Artificial Lake‐Level Lowering at Gepang Gath Lake, Indian Himalaya

“…The Poiqu basin (a transboundary Himalayan basin) hosts a number of potentially dangerous lakes and also has a history of at least six major GLOF events in the past (Allen et al., 2022). The Jailongco Lake is one potentially hazardous lake in the basin (Allen et al., 2019) from which two GLOFs occurred in 2002 (Chen et al., 2013).…”

“…Starting in 2018, the lake was lowered by 16 m, the frontal moraine was largely removed, and the outlet channel was stabilized with concrete. Recent modeling efforts show that there is a minimal effect on the GLOF magnitude and arrival time in a worst‐case GLOF triggered by a large ice avalanche with a failure volume of 18 M m 3 (Allen et al., 2022).…”

Glacial Lake Changes and Risk Assessment in Rongxer Watershed of China–Nepal Economic Corridor

“…Upper catchment area: The hydrological analysis module in ArcGIS is utilized to calculate this parameter. Large upstream catchment areas of glacial lakes can gather more rainfall and snowmelt, potentially leading to GLOFs [53]. The parameter is divided into three groups using the geometric interval method: high, medium, and low.…”

Enhanced glacial lake activity threatens numerous communities and infrastructure in the Third Pole

“…Additionally, existing glacial lake risk assessment schemes in the Third Pole are primarily qualitative or semi-quantitative, and empirical or simple models are generally used to simulate GLOF paths and are combined with a relatively rough downstream exposure 20 , 21 . Although these first-order studies help to identify priority areas of concern on a large scale, they are insufficient to determine detailed GLOF risks and specific exposure locations for individual glacial lakes or local development planning 22 .…”