Hillslope groundwater and river channel precipitation recharge to rivers in a continuous permafrost catchment of northeastern Tibetan Plateau

Climate-change driven degradation of permafrost and changes in precipitation have resulted in significant changes to hydrological processes in permafrost areas. Previous studies on hillslope-stream connectivity and associated runoff-recharge to rivers have mainly focused on the threshold conditions and processes. In contrast, there has been limited study on the capacity of the permafrost active layer to recharge rivers and the relationships between river channel precipitation and river runoff, needed to predict flood events. This study aimed to characterize river runoff generation processes in the Yakou Catchment, northeastern Tibetan Plateau. Continuous monitoring of meteorological variables (precipitation and air temperature) and hillslope hydrological elements (thaw depths, supra-permafrost groundwater, and the thickness of the saturated zone) was conducted between June-August 2021-2022. The results showed using the thickness of the saturated zone (TSZ) to determine wet and dry conditions yielded significantly higher low flow (average of 0.153 m3 s- 1) and lower low flow (average of 0.049 m3 s- 1) with average TSZ depths of 0.40 m and 0.12 m under wet and dry conditions, respectively. However, no significant difference was noted in quick flow. Precipitation during typical rainfall events deter-mined the generation of quick flow, with low flow constituting the main component of river runoff. The application of a partial least squares path model showed that TSZ on the permafrost determined the generation of river low flow which mainly originated from hillslope lateral subsurface flow. Conversely, river channel precipitation determined the generation of quick flow, which can contribute up to 80 % of the peak runoff during extreme rainfall events. Specifically, this study enhances the understanding of the connectivity between hill -slopes and rivers and the storage-discharge relationship in permafrost catchments. This study provides a new theoretical reference for simulations of hydrological processes in the permafrost region.

Automated summary

This study characterizes the processes of river runoff generation in the Yakou Catchment and highlights the importance of the thickness of the saturated zone and river channel precipitation in determining low flow and quick flow, respectively. The findings provide valuable theoretical references for simulating hydrological processes in permafrost regions.