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 m^(3) s^(−1);−61%)and high(+54.6 m^(3) 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.

A detailed reconstruction of changes in the factors and parameters of soil erosion over the past 250 years in the forest zone of European Russia(Moscow region)

Accelerated soil erosion is a major threat to soil,and there are great variations in the rate of soil erosion over time due to natural and human-induced factors.The temperate forest zone of Russia is character-ized by complex stages of land-use history(i.e.active urbanization,agricultural development,land abandonment,etc.).We have for the first time estimated the rates of soil erosion by the WaTEM/SEDEM model(rainfall erosion)and by a regional model(snowmelt erosion)over the past 250 years(from 1780 to 2019)for a 100-km2 study site in the Moscow region of Russia.The calculations were made on the basis of a detailed historical reconstruction of the following factors:the location of the arable land,crop rotation,the rain erosivity factor,and the maximum snow water equivalent.The area of arable land has decreased more than 3.5-fold over the past 250 years.At the end of the 20th century,the rates of gross erosion had declined more than 5.5-fold(from 28×10^(3) to 5×10^(3) t·ha^(-1)yr^(-1))in comparison with the end of the 18th century.Changes in the boundaries of arable land and also the relief features had led to a significant intra-slope accumulation of sediments.As a result of sediment redeposition within the arable land,the variation in net soil erosion was significantly lower than the variation in gross soil erosion.The changes in arable land area and in crop composition are the factors that have to the greatest extent determined the changes in soil erosion in this territory.