Quantitative Assessment Of The Effects Of Climate And Surface Cover Changes On Streamflow And Sediment Load Changes In The Mississippi River Basin

Under the influence of climate and surface cover changes,hydrological processes in most of the world's river basins are undergoing profound changes.As the fourth largest river in the world,the study on the spatial and temporal variation characteristics and driving mechanism of streamflow and sediment load in the Mississippi River is of great significance to the regulation of river and the sustainable management of river basin.On the basis of data collection of hydrometeorology,land use,dam system engineering and other data of the Mississippi River basin from 1930 to 2017,the Mann-Kendall trend,Pettitt mutation and Ensemble Empirical Mode Decomposition(EEMD)was used to analyze the spatial and temporal variation trend of climate,streamflow and sediment load.The effects of climate and surface cover changes on streamflow and sand change were quantitatively analyzed by using the coupled water-energy equilibrium equation and sediment identity factors decomposition.The main results are as follows:(1)The streamflow of the Mississippi River and its sub-basins all showed an upward trend,and the upward trend of all sub-basins except the Arkansas were significant.The Mississippi River and its sub-watershed streamflow mutation years are concentrated in 1972.The sediment load of the Mississippi River and its sub-basins all showed a downward trend.Among the four sub-basins,the Missouri showed the most obvious downward trend.The abrupt change years of sediment transport in the Mississippi River basin were 1975 and 1986.The annual distribution of streamflow and sediment transport was seasonal,mainly from march to May.The precipitation in the Mississippi River basin increased significantly and the temperature decreased,but the trend was not significant,and the potential evapotranspiration decreased significantly.(2)Since 1972,the slope of the linear regression relationship of streamflow and sediment load has decreased from 0.103 to 0.043,and the sediment transport capacity of the basin has decreased.Runoff in each sub-basin after 1972 had an extremely significant linear correlation with sediment load(p < 0.001),and the slope of regression relationship in Missouri river basin was higher than that in other three sub-basins,indicating that the sediment transport capacity in Missouri river basin was greater than that of other sub-basins.(3)Climate factor,streamflow and sediment load have similar short cycle change,the first two cycles can explain the most variable changes,and the residual term of sediment is bigger.Streamflow is mainly affected by climate change.In addition to the climatic factors,the sediment transport quantity is also affected by surface cover changes.The correlation coefficient between streamflow and precipitation in the Mississippi River and its sub-basins was 0.561(p < 0.01),while the correlation between sediment transport and surface cover factors such as dam storage capacity,embankment project length,farmland area and impermeable area was good.The double accumulation curve of precipitation and streamflow further shows that the Mississippi River has a good consistency between precipitation and streamflow,the latter is less affected by surface cover changes,but the consistency between precipitation and sediment load is poor,and the slope changes greatly in 1963 and 1985.(4)The absolute value of the elastic coefficient of streamflow on precipitation change in the Mississippi River and its sub catchment is the largest,ranging from 1.82 to 2.63,and runoff is the most sensitive to precipitation change.The contribution of precipitation to the increase of streamflow in the Mississippi River was the largest(up to 69.44%),followed by the contribution of underlying surface parameters(31.17%),and the smallest contribution of potential evapotranspiration(0.16%).The contribution of precipitation and underlying surface changes to runoff in Missouri river basin and upper Mississippi River basin was about half respectively,while the main influencing factor of streamflow in Ohio and Arkansas was precipitation,which contributed 68.13% and 76.11% respectively.On the whole,the runoff change of the whole Mississippi River basin is mainly affected by the precipitation change.(5)The main influencing factors of annual sediment transport quantity change in the Mississippi River and its sub-basins were analyzed by using the sediment identity factors decomposition.In the four sub-basins except the Arkansas river,the main influencing factor of sediment transport quantity change is the decrease of sediment concentration,and surface cover changes play a leading role in the decrease of sediment transport quantity.