The role of permafrost at Zonag Lake with its 2011 outburst: Insights from long-term and short-term perspectives

Abstract

Lakes across the Qinghai-Tibet Plateau (QTP) are experiencing widespread and accelerated expansion, with Zonag Lake representing an extreme case following its catastrophic overflow and outburst in 2011. However, the characteristics and changes of permafrost extensively distributed around the lake, as well as its role in the lake outburst, remain unclear. This gap in knowledge limits our accurate understanding of the causes behind the outburst of Zonag Lake and the expansion of numerous lakes on the QTP. In this study, by combining field monitoring and model simulations, we examined the role of permafrost in Zonag Lake outburst from both the long-term and short-term perspectives. Our findings reveal that low-temperature, highly ice-rich permafrost has developed around Zonag Lake. Transient permafrost modeling simulations indicate that the cold permafrost in this region has experienced a warming trend from 1961 to 2019. Notably, the warming rate of soil temperature was slower than that of air temperature, with changes in deep soil temperatures lagging behind those in shallow layers. The persistent presence of thermally stable permafrost surrounding the lake facilitates rapid convergence of precipitation recharge into the lake, thereby elevating its water level. Limited maximum thaw depth restricts the supply of meltwater from ground ice to the lake, resulting in approximately 80% (3.6 km 3 ) of the ground ice in the lake catchment being long-term trapped in permafrost. At the time of Zonag Lake outburst, the active layer was in the summer thawing stage, approaching the maximum thaw depth, and the thaw period was extended due to rising autumn temperatures. This stage of the year concentrated 80–90% of the annual precipitation, creating a window of opportunity for the lake's overflow and subsequent outburst. This study elucidates permafrost's role in the lake outburst and offers insights for predicting overflow risks, especially as QTP lake levels rise.