| Summary: | Quantification and modeling of runoff generation and hydrological processes operating in permafrost catchments are challenging. Active layer soil freeze-thaw cycles cause multifaced runoff generation processes with seasonal alternating patterns. By integrating soil temperature-based water saturation function into the soil water storage curve with a soil temperature threshold, we found that surface soil thawing induced saturation excess runoff and subsurface interflow account for approximately 66-86% and 14-34% of total spring runoff, respectively. Soil temperature significantly affects runoff generation patterns, runoff compositions, and runoff coefficients with the enlargement of the active layer. The supra-permafrost groundwater discharge decreases exponentially with active layer frozen processes during autumn runoff recession, whereas the ratio of groundwater discharge to total runoff and the direct surface runoff coefficient simultaneously increases. Based on the runoff generation processes and mechanisms, we developed a runoff generation model with temperature-induced variable source area (TVSA) for permafrost regions by coupling the active layer parameterization scheme, active layer freeze–thaw module, glacier module, and sub-permafrost groundwater module. The TVSA model was calibrated and validated using field observations in permafrost and glacier-affected Fenghuoshan and Tuotuohe watershed on the Qinghai-Tibet Plateau (QTP). Parameters related to the thermal conditions of the active layer and runoff processes were calibrated using the observed freeze and thaw depth data and the discharge data. The model successfully reproduced the freeze-thaw processes and discharges with high accuracy. The TVSA model is powerful for the systematic identification of variable source runoff generation processes and the associated physical mechanism under temperature control in permafrost basins.
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