Recent large inland lake outbursts on the Tibetan Plateau: Processes, causes and mechanisms

Abstract. Lake outburst events have been mainly focused on small glacial lakes in the Himalaya, while the historical events from inland large lakes are few and have received less attention. Inland large lakes on the Tibetan Plateau are expanding rapidly, with recent signs of increasing outburst risk, highlighting the need to elucidate the processes, causes and mechanisms to mitigate future impacts. Here, a long-term satellite lake mapping shows that the number and surface area of lakes on the Tibetan Plateau over the past 50 years peaked in 2023, accompanied by two notable outburst events: Zonag Lake (~150 km² in 2023) on 15 September 2011 and Selin Co (~2,465 km² in 2023, the largest lake in Tibet) on 23 September 2023. The cascading outburst of Zonag Lake caused its area to shrink by ~124 km² (-45 %), while the downstream Yanhu Lake expanded by ~163 km² (+347 %). The Selin Co outburst resulted in a water volume loss of ~0.3 Gt, the downstream Bange Co experienced a water level rise of ~2.3 m and an area expansion of ~18 %. Despite its large water storage capacity, Selin Co experienced less water loss due to the flat terrain at the breach and the slow flow (~1 m/s at the damaged road), with an average discharge of ~170 m³/s. Even with the low discharge, the Selin Co flood breached the lowland road within ~12 hours. In contrast, the large breach and steep terrain at Zonag Lake facilitated a rapid discharge of a sustained volume of water, with an average discharge of ~2,191 m³/s. Selin Co resulted in only a short period of drainage reorganization, in contrast to the permanent reorganization caused by Zonag Lake. The underlying mechanisms of the increased precipitation as the main trigger for the two outburst events prior to the occurrence are different. For Zonag Lake, thermodynamic effects, i.e. changes in the atmospheric moisture, are the most important, while for Selin Co, dynamical effects, i.e. the vertical motion induced by the changes in atmospheric circulation, dominate the precipitation patterns. Large lake outbursts in the Inner Tibetan Plateau are expected to increase in the near future due to the warmer and wetter climate, and urgent policy planning is needed to mitigate the potential future lake-induced flood damage.