Landscape Change And Ecological Risk Assessment Of Bahe River Basin In Shaanxi Province

Bahe River Basin is an important area for the supply of agricultural and sideline products and ecological regulation in Xi'an city.With the development of towns in the basin,the undisturbed natural landscape gradually decreases,and the landscape evolution will lead to the change of environmental factors,which will affect the ecological risk.This paper studies the landscape evolution and ecological risk of Bahe River Basin from the time and space scale,understands the spatial distribution of landscape in the study area,uses the method of ecological index modeling to quantify the comprehensive ecological risk of Bahe River Basin in the way of "geographic map",and explores the ecological risk changes of human settlements security area,product supply area and ecological regulation area under natural and human interference To provide basis for regional land management,development and spatial planning.Based on grid scale and township scale,the single ecological risk factor and comprehensive ecological risk of Bahe River Basin were evaluated.Firstly,the remote sensing images of 1995,2005 and 2015 were interpreted and modified by ENVI and ArcGIS to obtain the landscape types,analyze the landscape characteristics,and evaluate the habitat quality from the perspective of biodiversity based on the landscape structure;then,the elevation and fault area were selected Using SPSS,ANUSPLIN and other software and related mathematical models,the ecological risk assessment factors such as vegetation coverage,geological disaster susceptibility,drought and so on are calculated and analyzed.Finally,the weights of natural environment factors are determined by analytic hierarchy process,in which the weight of geological disaster index is 0.3971,the weight of vegetation index is 0.2726,and the weight of precipitation index is 0.3971 2071,and the weight of habitat quality index was 0.1232.Then the comprehensive ecological risk index was obtained by using the ecological risk assessment model.On this basis,using hot spot analysis tools and bivariate local Moran index,this paper explores the spatial distribution of the comprehensive ecological risk index in the study area,and analyzes the spatial correlation between ecological risk and land use intensity,so as to provide the basis for reducing ecological risk and promoting the sustainable development of the basin.The results are as follows:(1)Under the influence of natural and human factors,the Bahe River basin gradually evolved into a landscape spatial pattern with forest matrix in the southeast and farmland matrix in the northwest,river corridors running through the north and south,tributaries dividing the middle,and construction land patches concentrated along the river.At the level of landscape type,the landscape separation index division of the study area tends to 1,the patch density PD increases slowly,the maximum patch index LPI drops sharply to 22.75%,the proportion of the largest patch decreases under the interference of human activities,the large area matrix in the Bahe River Basin is gradually divided,the patch and corridor landscape types increase,the landscape fragmentation degree intensifies,and the landscape heterogeneity increases.The SHDI value of Shannon diversity is low,the richness of land use type is not high,while the Shei of Shannon evenness is close to 1,and the regional ecosystem is in a stable state.(2)From 1995 to 2005,the proportion of low habitat quality area increased from 3%to 8%,the proportion of medium habitat quality accounted for about one third of the total area,and the proportion of high and high habitat quality was the largest;Spatially,the annual average habitat quality in the southeast of Bahe River Basin was significantly better than that in the northwest,while the habitat quality in Baqiao street and Sanli town was poor;At present,the habitat quality is general,and it is easy to be disturbed and transformed into low habitat quality area.(3)The area of geological hazard prone area is 410.3km2,It accounts for 25%of the total area of the whole basin,and the geological disaster prone area is 389.5km2,Accounting for 23%of the total area of the study area,the geological disasters occurred mainly in the high risk areas of the central mountain area and the southern high risk areas.(4)From 1995 to 2005,the vegetation coverage decreased in the southeast of Bahe River Basin,FVC value decreased most obviously in bayuan Town,and the vegetation coverage increased in the middle;From 2005 to 2015,the vegetation coverage of each township increased significantly.(5)From the drought grade index,the study area was relatively dry in 1995,and no dry year in 2005 and 2015.The annual precipitation of Bahe River in the study area showed a fluctuating increasing trend.(6)The average comprehensive ecological risk index of Bahe River Basin was 0.356(1995),0.246(2005)and 0.254(2015),respectively,with significant difference in spatial distribution.From 1995 to 2015,the human settlements security functional area of Bahe River basin gradually changed from the ecological risk hot area to the non significant area,and the ecological risk gradually decreased.The hot spots of ecological risk in product providing function area changed from spot to lump,and concentrated in beibeiling area.Sanli Sanguanmiao town is the high concentration area of ecological risk.The ecological regulation function area is the cold point concentration area of ecological risk.