Modeling the water level regime of intrapermafrost waters and their runoff in Central Yakutia: A case study of the Eruu source catchment area

In permafrost regions, the combined effects of climate change and increased anthropogenic activity highlight the need to study the formation processes and dynamics of supraand intrapermafrost waters, due to their strong responsiveness to external influences. When continuous year-round observations are not possible, numerical modeling provides an efficient approach to study groundwater dynamics. This study aims to construct a mathematical model of suprapermafrost and intrapermafrost groundwater flow prevalent along the right bank of the Lena River in Central Yakutia, and to evaluate the interannual variability of these groundwater resources. A three-dimensional groundwater flow model was developed using the MODFLOW-USG software. This model was constructed using baseline data obtained from extensive, long-term field investigations in hydrogeology and geocryology conducted within the catchment area of a perennial icing spring located on the Bestyakh Terrace of the Lena River. The numerical model was calibrated using field-observed water levels from a monitoring well located within the intrapermafrost water transit zone. Calibration involved iterative adjustments of hydraulic parameters and boundary conditions until the deviation between simulated and observed intrapermafrost water levels was less than 0.1 m for more than 90% of the measurements. The simulation results enabled the reconstruction of the water yield dynamics in the intrapermafrost aquifer talik over the past 15 years, clarified the effects of various meteorological factors and seasonal freeze-thaw cycles on groundwater regime formation, and provided a quantitative evaluation of spring discharge variability at intra-annual scales. These findings establish a foundation for developing predictive frameworks of permafrost-hydrogeological evolution in response to climatic variability and provide a robust methodological approach for quantifying groundwater dynamics in permafrost-affected regions.