Modeling thermokarst lake expansion on the Qinghai-Tibetan Plateau and its thermal effects by the moving mesh method

- A dynamic model to simulate thermokarst lake growth was presented.
- Thermokarst lake expansion depended on lake-bottom temperature and permafrost temperature.
- Active thermokarst caused a greater thermal disturbance to permafrost.
- Lake expansion was not a good indicator for climate warming.

The increasing number of engineering activities on the Qinghai-Tibetan Plateau, along with a warming climate, tend to induce significant thermokarst processes. However, thermokarst lake development on the plateau and the long-term influence of thermokarst dynamics on the surrounding permafrost have not been fully understood. Based on the moving mesh method, we developed a dynamic model of lake growth with phase change to investigate the morphologic processes of a thermokarst lake and its long-term influence on the local permafrost thermal regime. Our numerical results indicated that lake expansion due to thermokarst development was fairly rapid, and it depended on many factors including lake-bottom temperature and permafrost temperature. The depth and radius of the simulated lake increased gradually from the end of May to the end of the following January, and remained stable from February to May due to the lower lake-bottom temperature. Our results also showed that lake expansion was not very sensitive to climate warming in the first 50 years after the formation of a thermokarst lake, but the lake expansion was clearly affected by a warming climate in the long run (200 years). The development of a thermokarst lake is shown to significantly enhance the thermal effects on the surrounding permafrost. Compared with a fixed-boundary thermokarst lake, an active (moving-boundary) thermokarst lake caused greater thermal disturbance to the permafrost around and beneath it.