A reference basin based framework for identifying and transferring permafrost hydrological coupling regimes across China

Abstract. Permafrost degradation is altering runoff generation, subsurface storage, and hydrological connectivity across cold region river basins. Scaling process understanding from well-studied basins to broader permafrost regions remains challenging because the subsurface hydrothermal controls that organize permafrost hydrological coupling are rarely observed at large spatial scales. This study develops a reference basin approach for identifying and transferring permafrost hydrological coupling regimes across China using simplified, broadly available, and process relevant proxy variables. Using the Source Region of the Yellow River as a process constrained reference basin, we construct a two-dimensional process space with two coordinates, dominant control depth DCD and coupling strength C. DCD describes the relative vertical position of hydrological control, while C represents the integrated magnitude of permafrost hydrological linkage. Temporal trajectories in this space are clustered into four coupling regime archetypes. These archetypes are then transferred to broader permafrost regions using a parsimonious proxy set that represents climatic background, topographic setting, and vertically integrated soil thermal organization. To define the applicability boundary, out-of-distribution screening identifies regions where target environmental conditions depart from the reference basin support. The results show coherent regional patterns of coupling regimes across the Qinghai Tibetan Plateau and northeastern permafrost regions, while out-of-distribution areas indicate where the transferred classification is less directly interpretable. The framework provides a bounded and physically interpretable pathway for scaling locally constrained coupling archetypes to broader data sparse regions.