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Changes in hydrological processes in the headwater area of Yellow River, China during 1956–2019 under the influences of climate change, permafrost thaw and dam
Discharge characteristics are crucial for detecting changes in hydrological processes. Recently, the river hydrology) in the Headwater Area of the Yellow River (HAYR) has exhibited erratic regimes (e.g., monotonously declining/low/high hydrograph, even with normal precipitation) under the effects of climate change, permafrost thaw and changes in dam operation. This study integrates hydroclimatic variables (air temperature, precipitation, and potential evapotranspiration) with anthropogenic dam operation and permafrost degradation impact data to systematically examine the mechanisms of these hydrological process changes during 1956–2019. The results show the following: 1) compared with the pre-dammed gauged flow, dam construction (January 1998–January 2000) and removal of dam (September 2018–August 2019) induced monotonously low (−17.2 m3 s−1; −61%) and high (+54.6 m3 s−1; +138%) hydrographs, respectively; 2) hydroclimatic variables mainly controlled the summer–autumn hydrological processes in the HAYR; 3) the monotonous decline of the hydrograph of Yellow River in the HAYR in some hydrological years (e.g., 1977, 1979, 1990 and 1995) was closely related with unusually high atmospheric demands of evaporation and low-intense rainfall during summer–autumn seasons; and 4) the lengthening of subsurface hydrological pathways and residence time, permafrost degradation reduced the recession coefficient (−0.002 per year) of winter flow and altered the hydrological regimes of seasonal rivers, which resulted in flattened hydrographs that reduced and delayed the peak flow (of 0.05 mm per year and 1.65 d per year, respectively) as well as boosted the winter baseflow (0.01 mm per year). This study can provide updated and systematic understanding of changing hydrological processes in typical alpine catchments on northeastern Qinghai–Tibet Plateau, China under a warming climate.