Temporal And Spatial Variation Of Runoff Sediment And Its Response To Human Activities In The PuHe Basin Of The Loess Plateau

The Loess Plateau is the main source of sediment in the Yellow River.In recent years,the sharp decrease of water and sand in the Yellow River and the frequent occurrence of flow breakage due to the influence of human activities and climate change are one of the hot spots of researchers'attention.Quantitative evaluation of the spatial and temporal variation characteristics of the Yellow River water and sand and its influencing factors is of great significance for the ecological protection of the Yellow River,scientific guidance of soil and water conservation in the Loess Plateau,and high-quality sustainable development of the Yellow River basin.The Pu River is a first-class tributary of the Jing River,an important tributary of the Yellow River,and one of the11 key tributaries in the construction of soil and water conservation ecological projects in the Yellow River basin.The surface of the basin is exposed,the vegetation cover is low,and soil erosion is serious.In this paper,we constructed a basin SWAT model to simulate the hydrological cycle of the Pu River basin from 2006 to 2019,evaluated the applicability of the model,analyzed the spatial and temporal evolution of runoff sediment and its influencing factors,and also adopted the Mann-Kendall trend test,the sliding t-test,and the one-dimensional linear method to investigate The evolution characteristics of runoff volume and sand transport in the Pu River basin from 1956 to990,and the influence of precipitation elements and human activities on runoff sediment changes were quantitatively analyzed by adopting the hydrological analysis method,and the main research conclusions are as follows.(1)The trends of runoff and sand transport in the Pu River basin from 1956 to1990 and the quantitative effects of precipitation and human activities on water and sand changes were elucidated.The runoff volume and sand transport volume are 216million m~3 and 44 million t,respectively,with sharp interannual variation and variation coefficients of 0.46 and 0.9,respectively,and 56.9%and 95.5%of the annual runoff volume and sand transport volume during the flood season,and the analysis of the results of the abrupt change trend test shows that the runoff volume and sand transport volume are significantly reduced,and the abrupt change year is around 1970,and the abrupt change before and after the abrupt change is significantly The runoff volume decreased by 25.6%and 39.2%before and after the mutation.According to the quantitative distinction between precipitation and human activities on the change of runoff sediment,the contribution of precipitation and human activities to the reduction of runoff was 49.9%and 50.1%,and the contribution to the reduction of sand transport was 54.0%and 46%,respectively,and the contribution of human activities was increasing.(2)The model base data were collected and the SWAT model of the Po River basin was successfully constructed to simulate the runoff sediment of the basin from 2006-2019 with high simulation accuracy.The SWAT-CUP tool with built-in SUFI-2 method was used to analyze the sensitivity of runoff and sediment parameters,and 11 runoff parameters and 7 sediment parameters with high sensitivity were finally determined to be used.The correlation coefficient(R~2),Nash coefficient(Ens)and relative error(Re)were used to evaluate the simulation results of the rate period and validation period,and the evaluation results showed that the SWAT model has high accuracy in simulating the process of runoff and sediment production and transport in the Puhe River basin,and is applicable in the Puhe River basin.(3)The spatial and temporal distribution characteristics of annual average precipitation,runoff depth,sediment load and evapotranspiration in the basin at different times were investigated.415.82 mm of annual average precipitation,306.80mm of annual average evapotranspiration,14.72 mm of annual average runoff depth,27.47 m~3/s of annual average runoff volume and 52.88 t/hm~2 of annual average sediment load were found in the sub-basin of Puhe River Basin from 2006 to 2019.The average annual precipitation,runoff depth,evapotranspiration and sediment load at the source of Ruhe River,a downstream tributary,are the highest in the basin.(4)Based on the model output,the main production areas of runoff sediment in the Puhe River basin were elucidated,and the influencing factors of water-sediment changes were analyzed.The middle reaches of the Pu River and its tributaries(Heihe River)and downstream tributaries(Ruhe River)have high water production,and are the main areas of runoff production in the Pu River basin;the main stream of the Pu River at its sources and middle and lower reaches,the middle reaches of its tributaries(Heihe River)and downstream tributaries(Ruhe River)have high annual sediment load and are the main areas of sediment production in the basin;the average multi-year precipitation is 407.0 mm,and the proportion of precipitation during the flood season is 73.2%,with an overall increase from northwest to southeast;grassland and The area of cropland accounts for more than 99%of the area of the Puhe River basin and is the main land use type in the basin.Based on the spatial distribution data of land use and the calculation of the land use transfer matrix,the mutual transformation of cropland and grassland is the main type of land use change occurring in the basin from 2006 to2019.The research can provide important reference for ecological protection,environmental governance,planning and development of Puhe River Basin.