Response Of Runoff And Sediment In Typical Watersheds Of The Upper Ganjiang River To Climate And Land Use Changes

The impact of climate change and human activities on river water and sediment changes has always been a hot issue in hydrological research.Quantitative analysis of the contribution rate of climate and human activities to changes in river water and sediment can provide a scientific basis for soil erosion control,land use and function adjustment in the basin.In this paper,the Taojiang River Basin in the upper Gan River is selected as the research area.According to Landsat TM / OLI remote sensing image data,precipitation data,and water and sediment data in the watershed,"3S" technology and mathematical statistical analysis are used to adopt Mann-Kendall trend analysis Sen slope estimation,Mann-Kendall mutation detection,sliding T test,cumulative anomaly,land use type dynamics,transfer matrix,landscape index,correlation analysis,double cumulative curve and other methods were used to analyze the average precipitation and extreme precipitation of 61 a in the basin.Dynamic changes,spatiotemporal changes in land use and their differentiation with topographic factors,dynamic changes in land use landscape patterns,and the correlation between precipitation,landscape patterns,and water and sediment have screened the precipitation indicators that characterize the best precipitation data,and then quantitatively analyzed The contribution rate of precipitation and land use to runoff and sediment transport in the basin.The main conclusions are as follows:(1)The annual average precipitation,precipitation in flood season,spring precipitation,summer precipitation,autumn precipitation,winter precipitation and precipitation intensity in the 61 a Taojiang River Basin all show insignificant increasing trends.Extreme precipitation indicators: number of moderate rain days,heavy rain days,heavy rain The number of days,moderate rain rainfall,heavy rain rainfall,heavy rain rainfall,maximum daily rainfall,and maximum rainfall for five consecutive days all showed a relatively significant increasing trend.(2)The main types of land use in the Taojiang River Basin are cultivated land and forest land.The sum of the two occupied 97.69%,97.52%,95.07%,and 93.23% of the total area of the basin in 1987,1997,2007,and 2017,respectively.Since 1987,the area of cultivated land in the Taojiang River Basin has been decreasing,mainly converted into forest land,grassland and construction land.In 99-300 m,flat land(slope 0 °-5 °),semi-shady slope(slope direction 22.5 °-112.5 °,292.5 °-337.5 °),the land use types are most abundant and diverse.Cultivated land and forest land are the dominant patches in the watershed.The distribution of forest land is more concentrated and fragmented than other land types;the distribution of grassland is the most scattered,with low connectivity and high fragmentation.Cultivated land is greatly disturbed by human activities,its area continues to decrease,connectivity decreases and fragmentation increases.Due to the conversion of cultivated land,the connectivity of woodland grassland is enhanced,the distribution tends to be concentrated,and the degree of fragmentation decreases.The area and number of plaques on the construction land have increased significantly,and at the same time,the connectivity has also increased year by year,and the planning is relatively concentrated.The combination degree,aggregation degree,connectivity and extensibility of the landscape in the watershed decrease,while the degree of fragmentation increases,the landscape becomes more diverse and the distribution becomes more and more uniform.(3)In the whole study interval,the annual runoff and flood season runoff showed a slight decrease and change trend,while the annual sediment transport and flood season runoff showed a more significant reduction change.2004 was a sudden change point of sediment transport in Taojiang River Basin.Based on this,the whole study interval was divided into two change stages: the base period of 1957-2004 and the change period(control measures period)of 2005-2017.In the change period,the annual average runoff and flood season runoff decreased by 47.93 × 108m3 and 63.23 × 108m3,respectively,while the average annual sediment transport and flood season sand transport decreased by 869.2 × 104 t and 655.1 × 104 t,respectively.During the reference period,the correlation coefficients between the annual runoff,flood season runoff,annual sand transport,annual flood season transport,and various precipitation indicators range from-0.2 to 0.95,while during the change period,the annual runoff,flood season runoff,and annual sand transport The correlation coefficient between the sediment transport in the flood season and each precipitation index is between-0.25 and 8.88;it indicates that the runoff sediment transport is more affected by precipitation in the reference period,and the runoff sediment transport is affected by precipitation and humans in the changing period.The dual impact of activities.In the entire study interval,reference period,and change period,spring precipitation is the most comprehensive precipitation indicator related to runoff and sediment transport.Watershed runoff is significantly negatively correlated with landscape pattern index DIVISION;sediment transport is significantly positively correlated with LSI,COHESION,CONTAG,and AI,and is significantly negatively correlated with SHDI and SHEI.The more diverse the land use landscape in the watershed and the more evenly distributed,the surface The stronger the ability to block water and sand.(4)Take spring precipitation as the best indicator to characterize precipitation to analyze the contribution rate of precipitation and human activities to the changes of water and sediment in the basin.The results show that the contribution rate of land use to runoff reduction during the change period is slightly higher than that of precipitation by 56.81%.The main factor affecting the reduction of runoff during the flood season is land use change,with a contribution rate of 81.79%.The contribution rate of land use to the reduction of sediment transport is much greater than the contribution rate to the reduction of runoff,which is the main influencing factor of the reduction of sediment transport in the basin.