Quantified hydrological responses to permafrost degradation in the headwaters of the Yellow River (HWYR) in High Asia

The impact on the hydrologic cycle of permafrost degradation under the influence of climate change has caused an inestimable threat to sustainable regulation of the ecosystem. This study quantified the responses of main hydrological elements, including soil moisture, groundwater, runoff components and discharge to totally degraded permafrost in eastern High Asia by establishing cases with and without thermodynamics using a cold region model combining hydrological processes and thermodynamics. The results showed that the model successfully simulated discharge in cold region basins. Totally degraded permafrost decreased soil moisture in the vadose zone (SMV) and increased the absolute depth to ground water (ADGW). In the daily scale, total permafrost degradation decreased the direct flow in autumn, slightly increased direct flow in spring and decreased interflow in summer. Total permafrost degradation also increased daily baseflow all year round and by >50% in spring, decreased daily discharge during autumn and increased daily discharge during spring. In the annual scale, total permafrost degradation increased direct flow, baseflow, and discharge, and decreased interflow. The magnitudes of these changes were positively related to the ratios of permafrost to the subbasin area. The responses of daily runoff components and discharge to totally degraded permafrost were significantly larger than the annual value. The groundwater level, direct flow and baseflow were far more sensitive to permafrost degradation than SMV, interflow and discharge. The responses of annual individual hydrological elements were more obvious than the annual discharge. These quantified results can be extensively used in lumped hydrology simulations, water resource assessments and eco-system management for partial permafrost degradation.