Study models worst-case glacial lake outburst floods showing >15× observed discharge in Himalayan basin

The study modeled worst-case glacial lake outburst flood scenarios for two existing dangerous lakes and a potential future lake upstream of Nyalam. Simulations considered large rock and/or ice avalanches as triggers for the outbursts. Results indicate that such avalanches could produce flood discharges at the Nepal border more than fifteen times larger than any previously observed or anticipated from gradual breach simulations. For all assessed lakes, warning times would be only five to eleven minutes in Nyalam and thirty minutes at the border.

Adopting the recommended approach would require investment in early warning systems, land-use zoning, and programmes to build local response capacities. Early warning systems must be capable of issuing alerts within the observed five-to-eleven minute window upstream. Land-use zoning that keeps critical assets out of the high-intensity flood zone may involve reassessing existing infrastructure locations. Programmes to build local response capacities involve training, equipment, and community drills to improve readiness.

The short warning times of five to eleven minutes in Nyalam and thirty minutes at the border constrain how much early warning can reduce loss of life or property. Recent lake-level lowering at Jialongco is found to have little influence on downstream impacts from a very large-magnitude outburst. Infrastructure already located within the high-intensity flood zone near Nyalam remains exposed even after such lowering. Therefore, depending solely on lake-level reduction or any single measure will not adequately mitigate the risk from worst-case scenarios.