Simulation of Freeze-Thaw and Melting of Buried Ice in Longbasaba Moraine Dam in the Central Himalayas Between 1959 and 2100 Using COMSOL Multiphysics

Permafrost degradation increases the likelihood of glacial lake outburst floods on the Tibetan Plateau. Analyses of the freeze-thaw conditions in moraine dams and associated impacts on dam stability contribute toward reducing natural hazard risks. We used the heat transfer module of COMSOL Multiphysics to simulate the soil temperature field in the Longbasaba moraine dam, which is on the northern slope of central Himalaya. There is close agreement between the simulated and observed soil temperature values. Root mean squared errors (the square root of the mean of the square of all of the error) are below 1.30? and mean bias errors vary from -0.10 to -0.52? for the different soil layers. Between 1959 and 2020, active layer thickness increased at a mean annual rate of 0.024 m a(-1). Under the Coupled Model Intercomparison Project Phase 6 scenarios, the buried ice inside the moraine dam is clearly melting. The maximum-buried ice thaw depth is currently 3.4 m and at the end of the 21st century is projected to be 9.53, 16.69, and 21.83 m under SSP1-2.6, SSP2-4.5, and SSP5-8.5, which indicates a continuous decrease in moraine dam stability.