Ecological Vulnerability Assessment Based On Soil Erosion In Gannan Tibetan Autonomous Prefecture

Scholars has paid more and more attention on The ecological environment in the Tibetan Plateau.Gannan Tibetan Autonomous Prefecture is located in the transition region between Tibetan Plateau and Loess Plateau,which is ecologically sensitive because of climate,topography and so on.Nowadays,grassland degradation and desertification,soil erosion,conflict between land use and ecological protection,pollution and other problems are increasingly prominent in this region.This paper takes Gannan Tibetan Autonomous Prefecture as the study area.According to the environmental characteristics of Gannan Prefecture,it uses meteorological statistics data,remote sensing image data,social and economic data and field investigation to explore the soil erosion situation and its spatial and temporal changes in Gannan Tibetan Autonomous Prefecture over the years.Based on soil erosion and other ecological indicators,this paper also explored the ecological vulnerability,spatial distribution and influencing factors of Gannan Tibetan Autonomous Prefecture.The results are as follows:（1）The erosion in Gannan Prefecture is dominated by slight erosion,which accounts for more than 84%of the area.The average soil erosion modulus in 2000,2010 and 2019was 255.56 t·km^-2·a^-1,406.13 t·km^-2·a^-1 and 406.88 t·km^-2·a^-1,respectively.The total area of moderate erosion and below grade continued to decrease,while The area of extremely intense erosion and severe erosion increased from 2000 to 2019.The average soil erosion modulus in the area of slight,intense,extremely intense and severe erosion also increased obviously,especially in the area of severe erosion,which increased by 2763.59 t·km^-2·a^-1.The average erosion modulus of mild and moderate erosion decreased.（2）The spatial difference of soil erosion in Gannan Prefecture is obvious,and the soil erosion intensity in the west is lower than that in the east.The areas of intense soil erosion were mainly distributed in the southwest edge of Maqu County,the north of Xiahe County,the southeast of Lintan County,the east of Zhuoni County,and part of Diabu County and Zhouqu County.The most severe erosion land use type in Gannan Prefecture is bare land.The policy of returning farmland to forest has a certain influence on the erosion intensity of cultivated land,woodland and grassland in Gannan Prefecture.In Gannan Prefecture,the deterioration of erosion is obvious in the areas where the vegetation coverage rate changes greatly.In addition,the erosion of Gannan Prefecture is mostly concentrated on the slope zone of 15°～45°.（3）The level of ecological vulnerability in Gannan Prefecture is high,and the proportion of moderately vulnerable areas is the largest in 2000 and 2010,and the proportion of severely vulnerable areas is the largest in 2019.The EVSI shows an increasing trend over time.From 2000 to 2010,both the potential vulnerable area and the mild vulnerable area decreased slightly.From 2010 to 2019,moderately vulnerable areas decreased and severely vulnerable areas increased.The level of ecological vulnerability in Gannan Prefecture is on the rise as a whole,and the ecological environment is deteriorating.（4）The spatial differentiation and spatial agglomeration of ecological vulnerability in Gannan Prefecture are obvious.The ecological vulnerability in the eastern and southeastern regions is lower than that in the northwest,the north and the southwest,and the potential vulnerable areas and the slight vulnerable areas are the main ones.The northwest,north and southwest were mainly moderate and severe vulnerable areas.In 2000,the northwest of Gannan Prefecture was the severely vulnerable area,the southwest was the moderately vulnerable area,and the potential vulnerable area and the slight vulnerable area were distributed in the southeast.In 2010,the severe vulnerability was distributed in the southwest,the severe vulnerability was distributed in the northwest,and the mild,mild and moderate vulnerability was mainly distributed in the eastern and northeastern regions.In2019,the ecological situation in the northwest and southwest is not optimistic,and the area of severely vulnerable areas is relatively large.（5）Bioindex,landuse,annual average temperature,population density,net primary productivity（NPP）,topographic undulation and altitude are the main factors affecting ecological vulnerability in Gannan Prefecture.Interaction detection results also revealed that all factors exist interaction enhancement effect,in the combination of the nonlinear enhancement,the interaction of the average annual precipitation and annual average temperature of Gannan ecological vulnerability has the strongest influence,in the combination of the bilinear strengthen,biological abundance index and landscape diversity index of Gannan ecological fragility strongest explanatory power.