Changes in Permafrost under Climate Change and Their Impacts on Eco-hydrological Processes: A Case Study of the Tibetan Plateau

Permafrost, a crucial component of the cryosphere, is mainly distributed in the high latitude and high altitude regions of the northern hemisphere, and is extremely sensitive to climate change. With global warming, permafrost is undergoing significant degradation worldwide, leading to substantial impacts on regional hydrological cycles, carbon cycles, ecological environments, and engineering construction. In our study, the Stefan’s solution and downscaled Coupled Model Intercomparison Project Phase 6 (CMIP6) datasets are employed to simulate the soil freeze depth, and the frost number model is utilized to calculate the frost number (F) based on the air freezing/thawing index derived from the downscaled CMIP6 datasets. A novel method was introduced to determine the optimal frost number threshold (F_t) to simulate the distribution of permafrost. The simulated permafrost distribution maps are compared with the existing permafrost distribution map to identify the optimal F_t with the Kappa coefficient as a measure of classification accuracy. Taking the Tibetan Plateau (TP) as a case study, the depth and distribution of permafrost were simulated under different Shared Socio-economic Pathways (SSP) scenarios on the TP. The changes in permafrost depth and distribution on the TP under different climate change scenarios and their impacts on eco-hydrological processes were analyzed. It is projected that the depth and area of permafrost will significantly decrease. Especially under the SSP585 scenario, by the end of the 21^st century, the permafrost of the TP will be almost completely degraded, and the regional mean SFD of the TP is projected to decrease by more than 50 cm compared to the current depth. The rapid decrease in the depth and area of permafrost on the TP may lead to a decrease in soil moisture and have adverse impacts on vegetation growth. This study provides valuable insights for understanding the changes in permafrost and their impacts on eco-hydrological processes.