ThawCoupler-1D (v1.0): A physically-based one-dimensional coupled thermo-mechanical model for simulating thaw subsidence in heterogeneous permafrost

Abstract. Permafrost thaw subsidence threatens infrastructure across Arctic and high-altitude regions and alters local hydrology. However, predicting the magnitude and rate of this deformation remains difficult due to the complex mechanical behavior of heterogeneous ground ice. Existing land surface models (LSMs) typically represent subsidence as a simplified geometric volume loss, omitting the transient dissipation of pore water pressure. Conversely, highly detailed geotechnical models are computationally expensive, making them impractical for multi-decadal, climate-scale simulations. To resolve these limitations, we developed ThawCoupler-1D (v1.0), a physically-based, computationally efficient finite-difference model designed to simulate thaw subsidence across highly variable ground-ice conditions. The model implements a threshold-based algorithm that switches between two settlement modes based on the initial void ratio: (1) large-strain thaw consolidation for porous soil matrices, governed by coupled heat transfer and pore water pressure dissipation; and (2) volumetric collapse for massive ice bodies (e.g., ice wedges), governed by phase-change kinetics and structural failure. The model utilizes a vectorized numerical scheme with an adaptive time-stepping algorithm constrained by the Courant-Friedrichs-Lewy (CFL) condition, allowing stable multi-decadal simulations at sub-daily and millimeter-level resolutions. We verified the model against analytical benchmarks and evaluated its performance using in situ borehole observations from the Beiluhe basin on the Qinghai-Tibet Plateau. The results show that ThawCoupler-1D reproduces the seasonal zero-curtain effect in thermal profiles and captures the non-linear settlement dynamics of both segregated and massive ground ice. Projections under CMIP6 scenarios indicate a critical thermal threshold, beyond which massive ice undergoes rapid volumetric collapse. This open-source code provides a tool for investigating thermo-mechanical feedbacks in degrading permafrost landscapes and improving sub-grid parameterizations in Earth System Models (ESMs).