Natural Disasters And Ecological Vulnerability Assessment In The Eastern Edge Of The Qinghai-Tibet Plateau

The eastern edge of the Qinghai-Tibet Plateau（EQTP）is located in the first step edge of China.With active geological activities and complex geological landforms,it is one of the most ecologically fragile areas in China.At the same time,EQTP is a transition zone for agriculture,forestry,and animal husbandry in western China,a transition zone between Han and minority,and a deep poverty area in the country.As the most densely populated area of the Qinghai-Tibet Plateau and the most disturbed by human activities,the grasslands in the EQTP have been over-exploited,deforestation,wetland reclamation,and steep-slope cultivated land for a long time.The extensive industrial development model has led to the decline of grassland and forest quality,and ecological problems such as desertification and “Black Soil Beach” have occurred in some areas.The contradiction between economic development and ecological protection is very acute.Therefore,the ecological vulnerability assessment of the EQTP will not only help to explore the mechanism and temporal and spatial evolution law of the regional ecological vulnerability,but also help to environmental protection and human activity control and promote regional green development.This study uses multi-source data such as disaster data,meteorological data,soil,vegetation data,land use and social economy to analyze the spatiotemporal distribution pattern of natural disasters in the EQTP.The ecological vulnerability evaluation system is constructed based on the Vulnerability Scoping Diagram（VSD）model.By this model,we evaluated the vulnerability of EQTP from 2000 to 2018,and analyzed the temporal and spatial distribution pattern of vulnerability.Finally,we use the geographic detectors model to analyze the influencing factors of vulnerability and analyze vulnerability patterns.The following conclusion are obtained:（1）Geological disasters and meteorological disasters occur frequently in the EQTP.Among them,earthquakes are mainly distributed in Longmen mountaion fault zone and Xianshui river fault zone,which are characterized by high magnitude and high frequency.Geological disasters are mainly landslides（40.3%）,debris flows（29.6%）,and collapses（15.4%）,mainly distributed in Huangshui river valley,Bailongjiang river main stream,Longmen mountaion fault zone.The EQTP is prone to droughts in summer and autumn.The north of Aba Prefecture to the eastern part of Gannan Prefecture is a high-incidence area of drought,which roughly presents a large-scale drought occurrence cycle of about three years.Different regions within the border area of the EQTP have different trends in drought.The drought in Qinghai Lake and its surrounding areas shows a significant downward trend,while the Hengduan Mountains shows a significant upward trend.The EQTP is most prone to snow disasters in winter and spring.The western Sichuan Plateau and the Qilian Mountains are the highincidence areas of snow disasters,showing a large-scale snow disaster occurrence cycle of 3-4 years.（2）From 2000 to 2018,the exposure,sensitivity,and adaptability of the EQTP generally showed a trend of increasing,little changing,and increasing,of which the exposure increased by 8.34% and the adaptability increased by 4.84%.Specifically,the exposure and sensitivity are generally high in the east and low in the west,and the adaptability presents a distribution pattern of high in the south and low in the north,and high in the east and low in the west.The high exposure areas are mainly distributed in the Longmen mountain fault zone,the Huangshui river Valley,and the main stream of Bailong River;the high sensitivity areas are mainly distributed in the Western Sichuan Plateau,Qilian Mountains and Gonghe Basin,and the low adaptability areas are mainly distributed in the Gonghe Basin,the Huangshui river valley,the Gonghe Basin,Alpine glaciers in Qilian Mountains and Shaluli Mountains.（3）The pattern of ecological vulnerability in the EQTP region from 2000 to 2018 generally showed a trend of increasing gradually from southeast to northwest.The vulnerability hotspots were mainly distributed in Qinghai Lake,Gonghe Basin,alpine glaciers in Qilian Mountains and Shaluli Mountains,Huangshui river Valley,Longmen mountain fault zone.The vulnerability cold spots are mainly distributed in the southern of Hengduan Mountain,Huangnan Prefecture to Gannan Prefecture.From the perspective of Prefecture,the highest ecological vulnerability are Haibei Prefecture and Hainan Prefecture,the lowest ecological vulnerability are Nujiang Prefecture and Gannan Prefecture.In general,the ecological vulnerability showed a trend of increasing first and then decreasing during the study period.The ecological vulnerability index（EVI）decreased the most in Hainan Prefecture（14.64%）and Haidong Prefecture（14.61%）,while Nujiang Prefecture,Diqing Prefecture and ecological vulnerability showed an increasing trend,and the EVI increased by 15.74% and 8.40% respectively..（5）The main factors affecting the spatial distribution of ecological vulnerability in the EQTP include normalized vegetation index,land use and land cover,Net primary productivity,soil erosion intensity and their Q values are 0.62,0.48,0.46 and 0.16 respectively,which indicating that vegetation and soil erosion factors have the greatest impact on ecological vulnerability.Among the climatic factors,precipitation（0.12）and the drought index（0.09）have higher effects on vulnerability than average temperature（0.03）,indicating that moisture are more important than heat.All factors have interactive enhancement relationship,most of them are double factor enhancement.Ecological vulnerability increases with increasing altitude,decreasing precipitation,and decreasing temperature.On a large scale,ecological vulnerability is dominated by climate and the vegetation adapted to it,and on a small scale,topography and human activities in some areas dominate.There are mainly three fragility modes in the eastern margin of the EQTP.The first is the intra-geological dynamics-dominated vulnerability represented by the Longmen mountain fault zone,the second is the climate-dominated vulnerability represented by the western Sichuan Plateau,and the third is the The human activity-surface activity synergy-domainted vulnerability represented by the Gonghe Basin and the Huangshui river Valley.