Landscape Pattern Change And Ecological Risk Assessment In The Yellow River Basin In Henan Province

In the process of urbanization,due to the strong interference of human activities,land use changes obviously,which leads to the reconstruction of landscape pattern.The change of landscape pattern will have a significant impact on the structure and function of the ecosystem,especially the ecosystem balance of the watershed with water area as the core.The Yellow River Basin in Henan Province is the ecological barrier of the North China Plain.It is great significant for ecosystem protection and ecological risk management of the Yellow River Basin in Henan province to reveal the change law of landscape pattern and evaluate the landscape ecological risk characteristics.Taking the Yellow River Basin in Henan Province as the study area,this paper extracted land use and vegetation cover data based on satellite remote sensing images,and analyzed the characteristics of land use change and vegetation cover change.On the basis of clarifying the characteristics of land use change,the spatio-temporal evolution of landscape pattern in the Yellow River Basin in Henan Province was analyzed.Based on the established landscape ecological risk assessment model,the characteristics of landscape ecological risk in the Yellow River Basin in Henan Province were evaluated,and the clustering characteristics of landscape ecological risk were identified by spatial autocorrelation analysis.The main research results are as follows:(1)Land use and vegetation cover data of the Yellow River Basin in Henan Province from 1990 to 2020 were extracted based on remote sensing images,and Arc GIS software was used to analyze the spatio-temporal evolution of land use and vegetation cover change.The results show that the proportion of cultivated land in the Yellow River Basin is the largest,followed by construction land and forest land,and bare land is the smallest.From 1990 to 2020,the area of cultivated land,grassland,shrub and bare land in the Yellow River Basin in Henan Province was in a downward trend,the area of forest land and construction land was in an upward trend,and the area of water area was fluctuating.The rate of land use change fluctuated,and the degree of land comprehensive use increased steadily.The vegetation coverage of the Yellow River Basin in Henan Province increased year by year from 1990 to 2020,and vegetation restoration has achieved remarkable results.(2)Based on land use classification results,Thirteen landscape indices,including the maximum type patch index(LPI),landscape shape(LSI),landscape aggregation(AI),patch density(PD)and Shannon diversity index(SHDI),were calculated by Fragstats4.2 software.The spatial and temporal changes of landscape pattern in the Yellow River Basin in Henan Province were interpreted from the perspectives of landscape overall level and type level.The results show that,from the perspective of time change characteristics,the overall landscape is stable,the shape has a regular trend,the degree of aggregation is enhanced,the degree of fragmentation is weakened,and the patch types are increased and evenly distributed.At the landscape type level,In terms of area shape,the area of cultivated land,shrub and grassland show ed a decreasing trend,the patch area of shrub and grassland had little change,and the water area showed a fluctuating trend of first increasing and then decreasing.The shape of grassland,construction land,woodland and cultivated land is complicated.In terms of convergence divergence,except for shrub and bare land,the aggregation degree of other landscape types showed a good trend.The landscape fragmentation of construction land,cultivated land,woodland and shrub decreased,the landscape fragmentation of grassland decreased first and then increased,and the landscape fragmentation of each weakened.From the perspective of spatial change characteristics,the spatial characteristics of the maximum patch index in the Yellow River Basin in Henan Province are higher in the west and lower in the east.Affected by urban expansion,landscape types tend to be regular.The agglomeration degree of landscape types was enhanced,while the fragmentation degree of landscape types was weakened.The range of landscape diversity was expanded,and the diversity of all landscape types was evenly distributed.(3)Based on the landscape ecological risk assessment model,the characteristics of landscape ecological risk in the Yellow River Basin in Henan Province were evaluated,and spatial autocorrelation analysis was used to identify the spatial agglomeration characteristics of landscape ecological risk.The research results showed that the overall characteristics of landscape ecological risk in the Yellow River Basin in Henan Province were high in the west,low in the east,and at the level of medium risk.The area of high risk areas fluctuated and distributed in Sanmenxia City and Luoyang City,while the area of middle risk areas decreased and mainly distributed in Mengjin County,Yuanyang County and Fengqiu County,while the area of low risk areas increased and mainly distributed in Fan County and Taiqian County of Puyang City.The distribution of landscape ecological risk in the Yellow River Basin in Henan Province was positively correlated with the spatial location.The local spatial clustering was dominated by high-high clustering distribution,while low-low,high-low and lowhigh clustering showed sporadic distribution and relatively dispersed distribution.