Spatiotemporal Changes Of Ecological Vulnerability In Ziwuling Area Based On The VSD Model

Global climate change and regional social and economic development have caused the natural environment and ecosystems to be disturbed to varying degrees,which has resulted in lots of regional and global ecological and environmental problems.The conflict between people and the environment has become increasingly prominent.Vulnerability assessment is one of the hot spots in geography and ecology research,and is also an important topic for regional sustainable development.The Ziwuling area,located in the hinterland of Chinese the Loess Plateau(hereafter CLP),as the junction of Shaanxi and Gansu Province,is the only natural secondary forest area in the CLP that needs to be well protected.However,due to the complex topography and landforms,this area has experienced a fragile natural-systems with serious soil erosion,although there is some forestland scattered,the forestland structure is single,and easily destroyed by the human activities,plant diseases and insect pests,and climate change.The ability to resist such disturbances reduce the risk is poor.At the same time,most of the counties and districts in the region are belong to old revolutionary bases and the national key counties for poverty alleviation and development.The infrastructure is poor too.There is a huge need to develop the economic and social levels.That is,the human activities are intensive and frequent.The conflict between regional economic development and environmental protection is sharp and serious.Therefore,study on the assessment of ecological vulnerability of Ziwuling area,to reveal the spatiotemporal changes of ecological vulnerability,is helpful to recognize the regional ecological environment status,which will be conducive to actively and effectively for environmental protection and human activity management,and enhance the green development in this area.In this thesis,Ziwuling area is selected as a case to study the spatiotemporal change of the ecological vulnerability for risk reduction and ecological protection.With the using of meteorological data,MODIS / Landsat TM remote sensing image data,land use and socio-economic data and related ecological models,based on the VSD(Vulnerability scoping diagram)model to build the ecological vulnerability assessment indicators system,to carry out the analysis of the spatial and temporal changes of ecological vulnerability and the contribution rate of its impact factors vis the hotspots analysis(Getis-Ord G*)and the geographic detectors;Then the OWA multi-criteria algorithm was used to simulate the ecological vulnerability scenario.Some suggestions were put forward for on the regional ecological environment protection and human activity management.The preliminary research results are as follows:(1)There are some apparent spatiotemporal differences of exposure,sensitivity,and adaptability in Ziwuling area from 1990 to 2017.The exposure showed an upward trend,among them,the growth rate of exposure between 1990 and 2000 was greater than that of 2010 and 2017,with larger increases including Wangyi,Ning County,Yingtai etc.,and a slight downward trend from 2000 to 2010.High exposure is concentrated in the north,southeast and southwest of the study area,and low exposure is concentrated in central and southern.Sensitivity generally shows a downward trend,with larger declines in Huangling,Xunyi,Yijun,Fuxian,etc.Among them,the changes from 1990 to 2000 are relatively small,from 2000 to 2010,the decline is the largest,and from 2010 to 2017,there is a slight downward trend,the spatial distribution pattern of sensitivity is similar to that of the exposure.Adaptability tends to increase,Yijun,Wangyi and Yingtai have a larger increase,and the spatial distribution is generally high in the east and low in the west.(2)From 1990 to 2017,the overall ecological vulnerability showed a downward trend,with a larger decline from 2000 to 2010.The spatial pattern is generally lower in the central and southern regions and higher in the northern and southwestern regions.From the perspective of spatial changes,the areas with significantly decresed ecological vulnerability are mainly distributed in the east of Wuqi,northwest of Zhidan,most of Yijun,Ansai and Ganquan local area.The areas of ecological vulnerability increased significantly are mainly concentrated in urban areas with frequent human activities.As the increasing of the altitude,the ecological fragility decreases first and then increases.The ecological condition in the low-altitude area(<750m)is the worst one,and the ecological environment in the middle-high altitude area(1150~1350m)is the best one overall.In the terms of land use types,the most ecologically vulnerable land types are the low-coverage grasslands in the arid area in the northern part of the study area,followed by construction land,unused land and arable land,while the high-coverage grasslands and woodland are less vulnerable.(3)There are change differences in the ecological vulnerability within and outside the core forestland.From 1990 to 2000,the comprehensive index of the ecological vulnerability in the surrounding areas of the core forestland showed an increasing trend,while the core forest showed a downward trend.From 2000 to 2010,the derease in SVI in and outside the core forest area was greater than that from 2010 to 2017.From 1990-2017,the ecological degradation areas were mainly concentrated in the surrounding areas of the core forestland.The distribution of the ecologically fragile cold hot spots is relatively concentrated,and the ecological vulnerability hotspots are mainly distributed in the northwest,northeast and southwest of the Ziwuling area.The cold spots are mainly distributed around the periphery of Huangling.(4)Impact factors and scenario simulation.The main factors which affected greatly on the spatial distribution of the ecological vulnerability in Ziwuling area includes: vegetation index EVI,biological abundance index,slope cultivated land ratio(>15°),soil erosion type,precipitation,and drought index,etc.Some of the most important factors were selected as the indicator for the scenario analysis with the consideration of the magnitude of all the impact factors.The scenarios included in the unsustainable orientation scenario(UOS),the maintaining status quo scenario(MSS),and the sustainability orientation scenario(SOS)were set up to simulate the change trend of the ecological vulnerability.The OWA multi-criteria algorithm was used to simulate and analyze the ecological vulnerability of Ziwuling area under the three scenarios.From “OUS” to “MSS” to “SOS”,the ecological vulnerability of Ziwuling area gradually weakened.Finally,some suggestions were put forward for the ecological improvement and environmental management for the Ziwuling area,which will be useful for the similar areas like Ziwuling in the Loess Plateau.