Analysis of groundwater flow through low-latitude alpine permafrost by model simulation: a case study in the headwater area of Yellow River on the Qinghai-Tibet Plateau, China

Warming climate and thawing permafrost have profound impacts on groundwater flow regimes in cold regions because of the shrinkage or disappearance of the confining unit formed by the permafrost layers and improving hydraulic connections. Numerical simulations of coupled groundwater flow and heat transfer are often used to characterize the changing permafrost hydrogeology. In this study, a number of scenarios for different hydraulic gradients and lake-water depths have been used to simulate the concordant permafrost evolution and groundwater movement using a two-dimensional cylindrical coordinate model at time scales of decades to centuries in response to a warming climate. The model is applied to a representative headwater catchment in the south-central headwater area of the Yellow River on the northeastern Qinghai-Tibet Plateau, China. The results show that the presence and movement of groundwater and the deeper subpermafrost aquifer can substantially accelerate permafrost degradation, and the disappearance of residual permafrost at depth can result in the sudden establishment of deep groundwater flow paths. All hydrological impacts will become evident after the stabilization of the hydrothermal and flow fields at 100–200 years. The stable discharge rate of groundwater flow varies from 8.0 to 12.4 m 3 s −1 , and the stable velocity of groundwater flow varies from 1.6 × 10 −7 to 4.4 × 10 −7 m s −1 under different scenarios within the model domain. The modeling results also demonstrate that flow velocity and discharge rate in local groundwater flow systems can be enhanced by an increased hydraulic conductivity, leading to an accelerated degradation of isolated permafrost bodies.