Runoff Variation And Simulation In The Source Region Of The Yellow River Under Climate Change

In recent decades,the hydrological situation in the source area of the Yellow River has undergone major changes due to global warming and increased human interference.The study of runoff evolution mechanisms and future runoff trends in the Yellow River source area in the context of climate change is of great significance for regional water resources management and protection.This paper takes the Yellow River source area as the research object.Firstly,based on hydrometeorological observations,NDVI and land-use remote sensing data,the characteristics of its hydrometeorological and subsurface changes are analysed.Secondly,the effects of climatic factors and human activities on annual runoff changes were quantitatively assessed using various attribution identification methods.To clarify the effects of vegetation changes on runoff,the contribution of climatic and human factors to vegetation changes was estimated using multiple linear regression equations.Then,based on the ABCD-SNOW model with coupled snowmelt module,a multi-scale Budyko runoff change attribution analysis framework was proposed to estimate the contribution of climatic factors and anthropogenic disturbances in runoff changes at different time scales in the Yellow River source area.Finally,based on the CMIP6 climate model data processed by statistical downscaling(Delta method),the ABCD-SNOW model was used to simulate and predict the runoff trends in the Yellow River source area under future climate change and socio-economic development scenarios.The main findings and conclusions of the study are as follows:(1)Linear regression,sliding average,Mann-Kendall test and double cumulative curve method were used to analyze the trend and test the sudden change of hydro-meteorological elements in the Yellow River source area from 1961-2018.The land use transfer matrix and Slope spatial trend analysis were used to reveal the evolution of the subsurface in the Yellow River source area.The results show that warming temperature and increasing precipitation are the main characteristics of climate change;annual runoff shows a non-significant decreasing trend and the decreasing rate in the wet season is much higher than that in the dry season,and the year of abrupt change in annual runoff is 1987.The land use pattern does not change much,and the vegetation index NDVI shows an increasing trend,with a spatially increasing trend from northwest to southeast.(2)Linear regression,sliding mean,Mann-Kendall test and double cumulative curve method were used to analyse trends in the hydroclimatic elements of the Yellow River headwaters basin from 1961 to 2018 and to test for abrupt changes.The land-use movement matrix and Slope spatial trend analysis were used to determine the evolutionary pattern of the substratum in the Yellow River headwaters area.The results show that warming temperatures and increases in precipitation and evapotranspiration are the main features of climatic change in the Yellow River headwaters area,with annual runoff showing a decreasing trend,the rate of decrease being much higher in the wet season than in the dry season,and the year in which annual runoff changed abruptly was 1987.Land use patterns have not changed much,and the vegetation index NDVI shows an upward trend,with an increasing spatial trend from north-west to south-east.(3)The multi-scale Budyko framework was extended based on the monthly ABCD-SNOW model to quantify the effects of climate change and human activities on runoff changes at different time scales.The results show that the coupled snowmelt module of the ABCD hydrological model performs well in the simulation of runoff from the Yellow River source area,capturing monthly runoff peaks and valleys better than the conventional ABCD model.Climate change and human activities caused runoff reduction effects at different time scales.Climate change caused 11.18 mm and 1.25 mm reduction in wet and dry season runoff in the Yellow River source area,respectively,while human activities caused 4.06 mm and 2.09 mm reduction in wet and dry season runoff,respectively,and climate change and human activities were the main controlling factors for wet and dry season runoff reduction in the Yellow River source area,respectively.(4)The ABCD-SNOW model,combined with climate model data downscaled by the Delta method and the climate elasticity coefficient method,is applied to simulate and predict the future runoff changes in the Yellow River source area.The results show that under the selected three scenarios(SSP126,SSP245,SSP585),the annual average temperature and annual average precipitation in the Yellow River source area from 2030 to2099 generally show an increasing trend,with a decrease in precipitation during the flood season and an increase in precipitation during the non-flood season.Under the influence of the above climate change,the average annual runoff of the Yellow River source area in the near and far future shows a slight decreasing trend,but the increase of dry season runoff and decrease of wet season runoff may alleviate the uneven distribution of its water resources within the year to some extent.The elasticity coefficients of water resources to changes in precipitation and temperature are 1.52～1.64 and-0.41～-0.72,respectively,and the sensitivity of water resources to changes in precipitation is much higher than that of temperature in the Yellow River source area.