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

Abstract. Research into lake outburst events has been mainly focused on small glacial lakes in the Himalaya, while historical events from large inland lakes are few and have received less attention. Large inland lakes on the Tibetan Plateau are expanding rapidly, with recent signs of increasing outburst risk, highlighting the need to elucidate their processes, their causes, and mechanisms to mitigate future impacts. Here, long-term satellite lake mapping shows that the number and surface area of lakes on the Tibetan Plateau have exhibited an increasing trend over the past 50 years, peaking in 2023. Two notable outburst events occurred during this period: Zonag Lake (∼ 150 km2 in 2023) on 15 September 2011 and Selin Co (∼ 2465 km2 in 2023, the largest lake in Tibet) on 21 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 mass loss of ∼ 0.3 Gt, and Bange Co downstream 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−1 at the damaged road), with an average discharge of ∼ 154 m3 s−1. Even with the low discharge, the Selin Co flood breached the lowland road within ∼ 10 h. In contrast, the large breach and steep terrain at Zonag Lake facilitated the rapid discharge of a sustained volume of water, with an average discharge of ∼ 2238 m3 s−1. 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 moisture motion induced by changes in atmospheric circulation, dominate the precipitation patterns. Large-lake outbursts on 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.