| A series of climate change issues such as Global warming,frequent natural disasters,and water shortages are largely the result of strong human interference and changes in the landscape structure.There is a long-term interaction between runoff and its change and landscape pattern,and the quantitative relationship between the two is deeply understood and simulated,it can not only provide theoretical support for solving the problems of sustainable utilization of water resources,water environment pollution and ecological environment protection,but also carry out the work of returning farmland to forest or grassland and protecting farmland,to provide practical guidance for establishing forest land vegetation management policy reasonably.Poyang Lake is China's largest freshwater lake,and Fuhe is its second largest watershed.In the past 20 years,the Fuhe River Basin's ecological environment protection and the projects of returning farmland to forests and grasslands have significantly changed the watershed landscape pattern,which will inevitably affect the hydrological cycle of the watershed and the entire Poyang Lake Basin.Research is also important for understanding regional water resources security.This paper takes the Fuhe River Basin as a case area,builds a SWAT hydrological model based on DEM data,land use data,soil data,and meteorological data,and verifies and evaluates the applicability of the SWAT model in the Fuhe River Basin,and recently simulated 31 sub-watershed the annual average surface runoff in three periods from 1990 to 1999,2000 to 2008 and 2009 to 2013.At the same time,the landscape pattern analysis method was used to analyze the dynamic changes of the landscape pattern in the Fuhe River Basin in 1990,2000 and 2008.Finally,combined with spearman correlation analysis method,quantitative analysis of the impact of landscape indicators on the surface runoff at the Fuhe sub-watershed scale.The main research conclusions are as follows:(1)The SWAT hydrological model of Fuhe River Basin was created,and after verification and verification,the model is highly applicable in Fuhe River Basin.31 sub-watersheds are divided,and the monthly average runoff of the sub-basins in three periods is simulated.Based on the SWAT-CUP SUFI-2 algorithm,sensitivity analysis,calibration and verification are performed.The results show that the simulated value and the measured value have a high degree of fit.The R2 and Ens of the three periods are 0.91,0.86,0.92 and 0.89,0.8,0.9,respectively.It can be seen that the SWAT distributed hydrological model has a very high accuracy in the Fuhe River Basin.(2)The annual precipitation and runoff of Fuhe River Basin from 1990 to 2013 showed a downward trend as a whole.The Mann-Kendall non-parametric test method and cumulative anomaly method are used to analyze the annual runoff changes in the Fuhe River Basin.There are roughly three stages:runoff rising stage from 1990 to 1999,runoff decreasing stage from 2000 to 2008,runoff Fluctuation phase from 2009 to 2013.There is a significant positive correlation between rainfall and runoff,indicating that rainfall and runoff are closely related,but the variability of runoff in the basin is much stronger than that of rainfall.Therefore,runoff is affected by two main factors,climate change and human activities,and the contribution rate of human activities to the decrease of runoff in the Fuhe River Basin increases,and even becomes the main factor affecting runoff.(3)In 1990,2000,and 2008,the eight landscape types have undergone violent spatial transformations during the two periods,but were in a dynamic balance during the study period.The cultivated land decreased by 1062.54 km2,the forest land expanded by 701.46 km2,and urban and rural construction land expanded by 306.89 km2 The wetland area increased by 16.36 km2 and the water area increased first and then decreased.Paddy fields and dry land are mainly transferred to forest land and urban and rural construction land;water areas are transferred to paddy field and forest land.From the landscape index,from 1990 to 2008,the degree of fragmentation increased first and then decreased,and the overall showed a decreasing trend.The shape of the patch became more and more complicated,and the connectivity first decreased and then increased,and the overall showed an increasing trend.Broken landscapes,and forest land has a greater degree of dominance in the Fuhe River Basin,with a high degree of connectivity between various types of patches.(4)At the landscape level,Patch Density(PD),Shannon Diversity Index(SHDI),and Shannon Equilibrium Index(SHEI)were significantly positively correlated with runoff,while Mean Patch Size(MPS)and Area-Weighted Patch Fractal Dimension(FRAC_AM)were significantly negatively correlated with runoff.Judging from the changes in the landscape pattern from 1990 to 2008,the degree of landscape fragmentation has weakened,the shape of the patch in the watershed has become more complex,and the uneven distribution of the patch has increased,while increasing precipitation interception and reducing runoff.There is a negative correlation between Contagion Index(CONTAG)and runoff,but the significant correlation is not strong;the Number of Patches(NP)has no significant correlation with runoff.(5)At the level of the landscape type,the landscape area ratio of dry land,paddy field,water area,urban and rural construction land patches has a significant positive correlation with Percentage of Landscape Index(PLAND)and runoff,while the forest land PLAND index has a significant negative correlation with runoff,and the forest land patch FRAC_AM is significantly negatively related to runoff,and the complication of the patch shape of the forest land enhances the interception of rainfall and plant transpiration by the surface,which reduces the runoff.The urban and rural construction land PLAND index,PD index and FRAC AM index are positively related.The expansion of urban area and the deepening of landscape fragmentation have reduced runoff consumption and promoted the increase of river runoff.Changes in landscape patterns have reduced runoff in the river basin. |
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