Evaluation And Regionalization Of Ecological Drought Vulnerability In Northwest China

Ecological drought vulnerability assessment is an important link in controlling and mitigating ecological drought,which can provide a scientific basis for mitigating losses caused by ecological drought and adjusting soil and water resources management strategies in the study area.However,there is a lack of quantitative assessment methods for ecological drought vulnerability.In this paper,taking Northwest China as an example,firstly,the ecological drought index(SEWDI)is constructed based on the ecological water deficit,and the concept of ecological drought vulnerability and quantitative characterization methods are proposed in three dimensions,including ecological drought exposure,sensitivity and impact,by combining the existing ecological drought vulnerability evaluation framework;secondly,the ecological drought vulnerability index(EDVI)is constructed by using a combination of hierarchical analysis and entropy weighting method to assign weights(The spatial correlation of the vulnerability index and the local spatial aggregation of vulnerability were assessed using the Moran index;finally,the spatial evolution characteristics of ecological drought vulnerability levels in Northwest China for three time periods from 1985 to 1994,1995 to 2004 and 2005 to 2014 were analyzed to make a comprehensive evaluation of ecological drought vulnerability in Northwest China.The following main conclusions were obtained.(1)The drought frequency was calculated based on the ecological drought index SEWDI,and the drought duration and drought intensity were extracted using the travel theory,and the ecological drought exposure index was constructed by combining the above drought characteristics with the NDVI weighted superposition.The exposure index for all levels is between 0.12 and 0.48,and the overall trend is increasing from west to east,among which the exposure is higher in Xinjiang Ili Basin,Tarim Basin,Qinghai Lake Basin,southern Qinghai,southeastern Gansu and most of Shaanxi,while the exposure is lower in northwestern Qinghai,southeastern Xinjiang and the surrounding areas.The exposure is lower in the surrounding areas of northwestern Qinghai and southeastern Xinjiang.(2)A Copula function was used to combine SEWDI and vegetation water use efficiency WUE to calculate the conditional probability of WUE increase under the drought intensification scenario,based on which the ecological drought sensitivity index was constructed by weighted superposition.The ecological drought sensitivity levels in the study area were divided into five levels: slight,mild,moderate,severe and extreme,and the sensitivity indices of all levels were located between 0.06 and 0.60,and showed a spatial distribution trend of gradually decreasing from north to south,especially in the Ili Basin,southeastern Qinghai,southern Gansu and southern Shaanxi,where the ecological drought sensitivity was low;while the Kunlun Mountains,Gansu,Ningxia and northern Shaanxi had(2)The sensitivity of ecological drought is higher in the Kunlun Mountains,Gansu,Ningxia and northern Shanxi.(3)The ecological drought impact index was constructed by weighted superposition of various ecosystem service values as indicators.The ecological drought impact levels in Northwest China were divided into five levels: slight,mild,moderate,severe and extreme,and the impact indexes of all levels were located between 0.02 and 0.91,with mild and slight impacts mainly,and the Qinling area was slightly impacted,while the areas of Northern Shaanxi and Guanzhong were severely or extremely impacted..The regions with higher impacts are mainly concentrated in the Junggar Basin,the area around the Tarim Basin,the Kunlun Mountains,the area around the Qaidam Basin,northern Gansu,northern Ningxia,and the area around northern Shaanxi and Guanzhong,while the impacts in the Altai Mountains in Xinjiang,the Ili Basin,eastern and southern Qinghai,southern Gansu,and southern Shaanxi are lower.From the analysis of the causes of ecological drought impact,it is found that the increasing arable land,forest land,and construction land make the value of ecosystem services rise,resulting in lower impact.(4)The ecological drought vulnerability in Northwest China has some regional heterogeneity,with the severely and extremely vulnerable areas mainly located in the Tarim Basin,Junggar Basin,the area around Turpan Basin in Xinjiang,Kunlun Mountains,the area around Qaidam Basin in Qinghai,Hexi Corridor,central and eastern Gansu,central and northern Ningxia,northern Shaanxi,and Guanzhong area in Shaanxi;the moderately vulnerable areas are mainly located in Xinjiang Altai Mountains,southwest Qinghai,near Qinghai Lake,southern Ningxia,and northern Shaanxi.The areas with higher ecological drought sensitivity have relatively higher ecological drought vulnerability.The spatial distribution of ecological drought vulnerability index in Northwest China is relatively aggregated and high,and the local spatial aggregation of ecological drought vulnerability shows an overall spatial distribution of "large aggregation and small dispersion".Ecological drought vulnerability tends to increase first and then decrease,but there is a deterioration trend of ecological drought in local areas.In addition,the vulnerability of Xinjiang Tianshan Mountains,Altay Mountains,central Gansu,central Ningxia,and most of Shaanxi showed an increasing trend after being improved,so the ecological drought vulnerability in the above areas should be further emphasized.The spatial distribution of the vulnerability index obtained in this study can provide a theoretical basis for the prevention and control of ecological drought in the study area,and the construction method of ecological drought vulnerability index can also be applied to other regions as a scientific reference for local ecological environment management.