Advancing hydrological understanding in cold regions: development and application of the WEP model for lateral flow estimation in the Great Lakes Depression of Mongolia

ABSTRACT In an era of rapid environmental change, accurately modeling aquatic ecosystems, particularly the lateral water flow through soil and permafrost, remains a pressing need. This study addresses this through the Water and Energy Transfer Process (WEP) model. The WEP model overcomes the limitations of previous models and plays a crucial role in estimating the lateral flow of groundwater in the basin. In this study, we use our new formula for calculating the lateral flow at the permafrost depth and the deep percolation formula to study the subsurface, over permafrost, and lateral water flows in the cold permafrost for 52 years (1970–2021). The model's application in Mongolia's Great Lakes basin, specifically the Khovd River-Khar-Us Lake basin, achieved Nash–Sutcliffe model efficiency (NSE) coefficients of 0.64–0.75. This suggests that the model is plausible and suitable for further research. Additionally, the model effectively captured soil temperature dynamics, with NSE coefficients ranging from 0.95 to 0.98 in the upper soil layer to 0.35–0.80 at a depth of 100 cm. These findings validate the model's ability to accurately account for lateral water flow above the permafrost layer in cold regions. Future work will extend these calculations to different conditions and basins.