A Study On The Hydrological Effects Of Climate Change And Human Activities In The Middle And Upper Reaches Of The Yellow River Basin Based On The SWAT Model

Global change is currently a hot issue of global concern.In particular,research on the water cycle and water resources under the influence of climate change and human activities has been paid more attention by scholars at home and abroad.Nowadays,in the context of global change,extreme weather events occur frequently,drought and flood disasters are prominent,and the contradiction between humans and the ecological environment is becoming increasingly acute,which seriously affects the sustainable development of society and ecology.The same is true for the Yellow River Basin.There are still serious soil erosion and harsh ecological environment problems in this area.Coupled with severe climate change and human activities,the problem of water shortage in the Yellow River Basin is further aggravated.Therefore,in view of this problem,this study conducted a detailed assessment and analysis of the impact of climate change and human activities on the water resources change of the Yellow River Basin,which has important reference significance for the scientific regulation of water resources,regional ecological balance and social sustainable development of the Yellow River Basin.In order to analyze the impact of climate change and human activities on hydrological process,this study uses the SWAT model to simulate the hydrological process in the upper and middle reaches of the Yellow River Basin,and quantitatively analyze the causes of runoff changes under climate change and human activities;In addition,the climate forcing data under future scenarios is also used to predict the changes in runoff and water resources under future scenarios.In addition,in order to better simulate the hydrological effects of the watershed under the change of vegetation,this research has optimized and improved the vegetation growth process and the input mechanism of driving data in response to the insufficiency of the vegetation growth and evapotranspiration algorithms in the original SWAT model.The evapotranspiration algorithm in the original model is improved,which improves the applicability of the model in the upper and middle reaches of the Yellow River Basin.In this paper,SWAT model is used to study the causes of runoff and evapotranspiration changes in the Yellow River Basin,and the main conclusions are as follows:(1)In terms of climate change,precipitation generally showed a relatively gentle downward trend from 1960 to 2017;while the minimum temperature and the maximum temperature showed a relatively obvious upward trend.In terms of land use changes,a large area of bare land,arable land,and sandy land was converted into forest land.grassland and construction land during 1990-201 5.(2)Changes in climate and land use have reduced the natural runoff of the upper and middle reaches of the Yellow River Basin.The contribution rate of climate change to runoff is 59.97%,and the contribution rate of land use change is 59.97%.40.03%.The impact of climate change on runoff is mainly distributed in the watersheds controlled by Tangnaihai and Guide stations in the upper reaches of the Yellow River,and Linjiacun,Zhuangtou and Hejin stations in the middle reaches,and its contribution to runoff is between 73%and 85%;and land use changes The impact on runoff is mainly distributed in the basins controlled by Lanzhou,Toudaoguai,Longmen,Huayuankou and Zhangjiashan Station in the middle reaches of the Yellow River,and its contribution rate is between 39%and 53%.(3)The main reason for the decrease in measured runoff(Huayuankou Station)in the upper and middle reaches of the Yellow River Basin is due to human activities.The impact of human activities on the changes in the measured runoff(Huayuankou Station)dominates,with a contribution of 67%;while climate change contributes 33%to the runoff.The impact of human activities on runoff is mainly reflected in the middle reaches of the Yellow River,especially the basins controlled by Zhangjiashan,Toudaoguai,Longmen and Huayuankou;in the upper reaches of the Yellow River,Tangnaihai,Guide,and Linjiacun,Zhuangtou and Hejin,which are tributaries of the middle reaches of the Yellow River.In the basin controlled by the station,the impact of climate change on runoff is higher than the impact of human activities.(4)Compared with the base period,the amount of precipitation and the minimum and maximum temperatures in the future scenarios will increase to a certain extent.From the perspective of the intra-year variation characteristics of meteorological elements,the increase in precipitation is mainly from May to July,the increase in the minimum temperature is mainly in May-September and winter,and the increase in the maximum temperature is concentrated in July-September.In addition,the runoff and water resources under future climate change scenarios are both higher than the baseline period.From 2021 to 2100,the average annual runoff under SSP126,SSP370 and SSP585 scenarios increased by 83.52%,42.13%and 31.63%,respectively.In addition,the amount of water resources in the Yellow River Basin will increase by 52.31%between 2021 and 2100.All in all,with the increase in the amount of water resources in the future,the pressure on water resources in the Yellow River Basin will be alleviated.(5)The evapotranspiration simulated by the improved SWAT model is superior to the simulation results of the original model both in space and time.In addition from 1984 to 2015,evapotranspiration showed an annual growth trend of 2.60mm,and showed a significant increase after 2000.Among the components of evapotranspiration,vegetation transpiration increased at a rate of 2.48 mm per year,and evapotranspiration began to show a significant upward trend in 1998;soil evaporation as a whole showed a downward trend at a rate of-0.07 mm per year,and the overall change Relatively gentle;canopy interception presents an increasing trend of 0.20mm per year.The rate of increase in vegetation transpiration is the most obvious,which is the direct cause of the significant increase in evapotranspiration.(6)The effect of leaf area index change on evapotranspiration is obviously stronger than precipitation,temperature and potential evapotranspiration.Partial correlation analysis of evapotranspiration with leaf area index,potential evapotranspiration,precipitation,and temperature found that the spatial positive correlation between evapotranspiration and leaf area index was the highest;while the correlation with temperature and precipitation There is a certain positive correlation;the correlation with potential evapotranspiration shows a negative correlation as a whole,and a positive correlation in a local area.