Impacts of permafrost thaw on streamflow recession in a discontinuous permafrost watershed of northeastern China.

Permafrost thaw due to climate change is altering terrestrial hydrological processes by increasing ground hydraulic conductivity and surface and subsurface hydrologic connectivity across the pan-Arctic. Understanding how runoff responds to changes in hydrologic processes and conditions induced by permafrost thaw is critical for water resources management in high-latitude and high-altitude regions. In this study, we analyzed streamflow recession characteristics for 1964-2016 for the Tahe watershed located at the southern margin of the permafrost region in Eurasia. Results reveal a link between streamflow recession and permafrost degradation as indicated by the statistical analyses of streamflow and the modeled ground warming and active layer thickening. The recession constant and the active layer temperatures at depths of 5, 40, 100, and 200 cm simulated by the backpropagation neural network model significantly increased during the study period from 1972 to 2020 due to intensified climate warming in northeastern China. The onset of seasonal active layer thaw was advanced by 10 days, and the modeled active layer thickness increased by 54 cm in this period. The average annual streamflow recession time increased by 11.5 days (+53 %) from the warming period (1972-1988) to the thawing period (1989-2016), with these periods determined from breakpoint analysis. These hydrologic changes arose from increased catchment storage and were correlated to increased active layer thickness and longer seasonal thawing periods. These results highlight that permafrost degradation can significantly extend the recession flow duration in a watershed underlain by discontinuous, sporadic, and isolated permafrost, and thereby alter flooding dynamics and water resources in the southern margin of the Eurasian permafrost region.