| Climate change and human activities are two key factors affecting the hydrological process,which can lead to significant changes in river runoff and sediment transport,and are important factors that cannot be ignored in river water and sediment management.To understand the evolution characteristics of runoff and sediment transport and scientifically understand the impacts of climate change and human activities on runoff and sediment transport are the prerequisites for realizing sustainable development of river basins.However,most previous studies focused on the single impacts of climate change or human activities,ignored the combined impacts of climate change and human activities on water and sediment and their complex mechanism processes,and did not deeply understand the impacts of specific types of human activities(such as land use)on the evolution of water and sediment and the similarities and differences between adjacent basins.In this study,Xiangjiang River,Zijiang River,Yuanshui River and Lishui River(the four rivers in Hunan Province hereinafter referred to as Xiang,Zi,Yuan,and Li)are taken as the research object.Based on the runoff,sediment transport,precipitation and land use data,using Mann-Kendall trend test,Pettitt test and Pearson correlation analysis to study the spatial-temporal variation characteristics of runoff and sediment transport,compare the differences of water and sediment variation among the four basins,and quantify the impacts of climate change and human activities on runoff and sediment transport,and explore the correlation between land use change and sediment transport,which could provide reference for water resources management and land use planning in the basin.The main results of this study are as follows:(1)From 1988 to 2019,forest and farmland are the main land use types with the largest area change in the Xiang,Zi,Yuan,and Li River Basins.On the whole,farmland conversion into forest is the main land transfer type in Four Rivers Basin of Hunan.(2)Except for the Xiangjiang River and Yuanshui River Basins,there are significant differences in the runoff and sediment transport between the other Xiang,Zi,Yuan,Li River Basins(p<0.01).The average annual runoff(656.16×108m3 yr-1)and sediment transport(840.29×104Mg yr-1)of Xiangjiang River Basin are the largest.The annual average runoff modulus(94.20×105m3s-1 km2)and sediment transport modulus(287.91 ×104Mgs-1 km2)in the Lishui River Basin are the highest.(3)There are similarities and differences in the evolution characteristics of runoff and sediment discharge in different basins.The sediment transport in the four basins showed a significant decreasing trend(p<0.001),while the runoff showed no significant change trend.In terms of time,there are significant abrupt changes in sediment transport in the four basins of Xiang,Zi,Yuan,and Li,with abrupt changes occurring in 1985,1999,1996,and 1983,respectively.However,there is no significant abrupt change point in runoff.Wavelet analysis found that the first main periods of runoff are 28 years,29 years,28 years and 27 years,respectively;and the first main periods of sediment transport are 28 years,14 years,20 years,and 27 years,respectively.(4)The interannual variation of runoff is mainly influenced by climate change,and has the greatest impact on the runoff of the Lishui River Basin.The Sediment transport is mainly affected by human activities.In Xiang,Zi,Yuan,Li Basins,the contribution of human activities to the sediment transport is 80.60%,94.90%,102.13%and 84.98%,respectively,and it was the largest contribution to the sediment transport in Yuanshui River Basin.(5)The relationship between land use and sediment transport is different in different basins.In Yuanshui River Basin,there are 6 types of land use and sediment transport significantly correlated,but in Xiangjiang River Basin,sediment transport is only significantly correlated with 1 type of land use and weakly correlated with 3 types of land use.In addition,the influence of land use change area on sediment transport is different in different basins.The results show that there are differences in the long-term variation characteristics of runoff and sediment transport among the four river basins of Xiang,Zi,Yuan,Li,and the main influencing factors are different.It indicates that the management policies of river basins should be formulated according to the water points of different basins.Based on high-precision continuous time series land use data,this study can more accurately detect land use change and more completely understand the relationship between land use change and sediment discharge.The results of this study can provide a scientific basis for water resources management in the basin,and can provide methods,results and theoretical basis for formulating related land use policies,follow-up research of researchers in related research fields and sustainable development of the basin. |
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