Analysis Of The Relationship Between The Environment,Human Factors And The Change Of Water And Sediment Into The Yellow River In The Past 100 Years

The He-Long section is the main water and sediment source area of the Yellow River,and the area with the most serious soil erosion in the Yellow River Basin,so it has become a key area for the Yellow River Basin governance.In the past 100 years,major changes have occurred in the water and sediment in the He-Long section.In order to explore the driving factors for these changes,this study selected factors such as temperature and precipitation,population,arable land area,vegetation coverage,and soil and water conservation measures.Chronology,Mann-Kendall mutation test,Empirical Mode Decomposition(EMD),Pettitt mutation test,double cumulative curve,cumulative anomaly method,and ordered clustering analysis methods were used to analyze the trends and mutations of the climate change,human activity,and hydrological sequence of the He-Long section from 1919 to 2016.Based on this,the hydrological sequence was divided into five phases,and the factors affecting the changes in water and sediment were analyzed in stages.The main conclusions are as follows:(1)Reconstructed the Fractional Vegetation Cover(FVC)in the He-Long area for nearly 100 years.Correlation analysis results showed that FVC and tree rings had a high correlation with summer precipitation and spring temperature.When the temperature is high in spring and the rainfall is abundant in summer,the plants grow better and the coverage is higher.The FVC from May to October had a high correlation with the tree-ring width index(P <0.01).Based on this,the tree-ring width was used to reconstruct the coverage from 1888 to 1981,and the remote sensing observations from 1982 to 2016 together constitute a time series of FVC in the He-Long area in the past 100 years.Analysis of the FVC time series found that in the past 100 years,there have been 20 high-coverage years and 21 low-coverage years,accounting for 15.5% and 16.3% of the total reconstruction years,respectively.There were four periods of low vegetation coverage(1924-1929,1931-1935,1982-1987,2003-2007),which was consistent with the record of drought events.(2)Analyze the changes of climate and human factors in He-Long area in the past 100 years.In the past hundred years,the climate distribution in the He-Long area had shown that the temperature in the south is higher than that in the north and there is more precipitation,and the spatial distribution of water resources is uneven.The interannual changes in temperatureand precipitation are similar to the general environment: the temperature has a trend of increasing year by year.The precipitation is stable at about 400 mm except for the low precipitation around 1930.The change of human factors had phases,and the driving factors were social development and government policies.Before 1949,social turbulence,slow population growth,less arable land,less afforestation,more firewood felling,and certain damage to forest and grass.From 1949 to the 1970 s and 1980 s,the society was stable,the population increased,the cultivated land area increased,the vegetation was destroyed,and the soil and water conservation measures were less effective.After the 1980 s,the state paid more attention to environmental protection,implemented “Family Planning” policies,carried out “shelter-forests in Northern China” construction,standardized terraced fields,silt dam construction,and implemented the policy of “Return Farmland to Forest”.The effect of soil and water conservation measures is remarkable.(3)Analyzed the coordinated evolution law of climate change,human activities and water and sediment in He-Long area.According to the analysis results of the double cumulative curve,it can be determined that the catastrophic years of runoff and sediment transport in the He-Long area in the past 100 years are 1971 and 1979,respectively.Based on this,combined with the phase of human activities,the hydrological sequence is divided into five stage.From 1919 to 1949,frequent wars,economic and social turmoil,water and sediment changes were mainly affected by climate change.From 1950 to 1980,climate change was still the decisive factor,but soil erosion has further intensified due to population growth,cultivated land reclamation,and deforestation.Meantime,soil and water conservation measures were implemented,and soil erosion were controlled to a certain extent.In this period,both climatic conditions and human activities affected the changes of water and sediment.After 1980,soil and water conservation measures were further strengthened,coupled with the Grain to Green Project,the water and sediment in He-Long section drastically decreased.Human's activity played a leading role.(4)Revealed the attribution of water and sediment changes in He-Long area in the past 100 years.The results of principal component analysis show that from 1919 to 1979,the relative contribution rates of natural factors and social factors to runoff changes were 56.2% and 43.8%,respectively.The impact of cultivated land area among social factors was higher than other factors.Natural factors were the main factors affecting sediment transport.From 1980to 1996,the relative contribution rates of social factors and natural factors to sediment transport were: 48.7% and 51.3%,and the relative contribution rates to runoff were: 46.8% and 53.2%.Among the social factors,the relative contribution rate of population factor,cultivated land factor and warping dam factor was similar,and the relative contribution rate of afforestation factor was low.From 1997 to 2016,natural factors were no longer the main factors affecting water and sediment changes.Runoff was greatly affected by afforestation area,and sediment transport was greatly affected by silt dams and terrace construction.