Impacts Of Permafrost Thaw On Streamflow Components In The Da Hinggan Mountains Watersheds

Permafrost thaw due to climate change is altering terrestrial hydrological processes by increasing ground hydraulic conductivity and surface and subsurface hydrologic connectivity across the northern areas,especially the river base flow from groundwater and soil water.Understanding how streamflow and baseflow responds to changes in hydrologic processes and conditions induced by permafrost thaw is critical for water resources management in highlatitude and high-altitude regions.In this study,the permafrost watershed of Da Hinggan Mountains were used to determine the trends in long-term hydrometeorological data,the relationship between hydrological variables and the changes in climate and permafrost.The results showed that:(1)There was significant permafrost thaw in the Tahe and upstream of Huma watershed.The thawing index of the indicators of permafrost degradation has a significant positive trend(P<0.05)from 1972 to 2020.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.The onset of seasonal active layer thaw was advanced by 10 days,and the modeled active layer thickness increased by 17 cm in this period.(2)Permafrost degradation is the major driver regularing recession process(P<0.001).The average annual streamflow recession time increased by 11.5 days(+53%)from the warming period(1972-1988)to the thawing period(1989-2016).(3)The impact of permafrost degradation on streamflow components shows significant differences in different watershed.The recession constant in the Tahe and the upstream of Huma all displayed significant upward trends(P<0.05),with trend of 0.0002/a and 0.0004/a from 1964 to 2016.The annual and thawing BFI of the Tahe and the upstream of the upstream of Huma watershed showed downward trend,while the baseflow index in the frozen season displayed an upward trend.In addition,the increase or decrease of streamflow,baseflow and baseflow index in the Tahe are faster than those in the upstream of Huma.(4)There was a sinificant effect of permafrost degradation on the baseflow in watershed,and the impact degree was different under different permafrost coverage area.The result of quantifying the relative hydrologic effects of climate variability and permafrost thaw on streamflow and baseflow indicated that the contribution of permafrost degradation to the change in streamflow and baseflow was 22.43% and 20.67% in the Tahe watershed,and 17.31% and15.26% in the upstream of Huma watershed.