| The Lhasa River is one of the tributaries with the largest runoff and confluence area of the Yarlung Zangbo River on the Tibetan Plateau,China.Human activities such as population growth and urbanization cause land use changes in the Lhasa River basin,which change the landscape structure of the river basin,and in turn affect the process of runoff and sediment.Therefore,the research on the evolution characteristics and driving mechanism of the runoff and sediment processes under the changes of land use and landscape pattern in the Lhasa River basin will provide scientific guidance for comprehensive management of water and soil resources and rational planning of land use.In this study,the accumulative anomalies and Mann-Kendall test were applied to explore the evolution trend and mutation characteristics of precipitation and runoff in the Lhasa River basin.Arc GIS and other software were used to study the temporal and spatial evolution of land use.The SWAT model and RUSLE model were used to simulate the runoff and sediment processes.The characteristics of water production and soil erosion in the subbasin and their responses to land use changes were analyzed.Pearson correlation analysis was used to explore the impact of the landscape pattern changes on the runoff and sediment process.The main research conclusions are as follows:(1)Human activities are the main factor influencing the change of runoff from2005 to 2016.The reduction of arable land,grassland,and forest land and the transition of various land use types to built-up land constitute the dominant process of land use change from 2010 to 2015.The transition between different land use tends to be complex and changeable is the manifestation of dynamic changes from 2015 to2020.(2)The simulation results of the SWAT model show that the NSE of Tangga and Lhasa hydrological stations are 0.74 and 0.75,and R~2 are both 0.76.The NSE of the verification are 0.66 and 0.67,and R~2 are 0.69 and 0.68,respectively.The result of simulation is valuable and can describe the hydrological process of the Lhasa River basin accurately.The annual average water production decreases in the order:2020land use scenario>2015 land use scenario>2010 land use scenario;arable land scenario>grassland scenario>forest land scenario.Forest land and grassland have the effect of reducing water production.The water production in the middle and south is more than that in the west and northeast of the basin.(3)The average soil erosion modulus is the highest in 2015 and the lowest in 2020.The soil erosion in the basin is distributed in strips,flakes and dots.The erosion modulus gradually decreases from the Serong Zangbo area in the middle reaches of the Lhasa River to the periphery.The unused land has the highest soil erosion modulus,arable land has the lowest soil erosion modulus.(4)From 2010 to 2020,the landscape pattern develops towards fragmentation,the complexity of the landscape shape increases,the degree of aggregation decreases,and the impact of human activities is increasing in the Lhasa River basin.At the landscape level,the correlation coefficients between the landscape index,water production and soil erosion variables are low.At the type level,there are differences in the signs of the correlation between the landscape pattern index,water production,and soil erosion.Therefore,the land use pattern and landscape types should be optimized to gradually reduce the runoff and sediment transport in the Lhasa River basin. |
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