Study On Spatiotemporal Changes And Driving Factors Of Vegetation Coverage The Chengdu-Chongqing Economic Circle

Vegetation is one of the basic components of terrestrial ecosystems and an important link between different layers of the earth,playing a crucial role in regulating carbon cycle,water cycle,soil and water conservation and mitigating greenhouse effect in many aspects.The Chengdu-Chongqing Economic Circle is located in the upper reaches of the Yangtze River and the southeast of the Qinghai-Tibet Plateau in China.The region has a complex natural environment and is an important area for population,urban and industrial clustering,which plays a very important role in both economic development and ecological environment.Investigating the spatial and temporal variation characteristics of vegetation cover and its driving factors in this region is of great scientific and practical significance for understanding the current state of the ecosystem,maintaining the balance of the ecosystem,and promoting the sustainable development of the ecosystem.In this study,based on multi-source data such as GLASS FVC data,meteorological data,topographic data,vegetation type,soil type,night light index,GDP and population density from 2000 to 2021,we used one-dimensional linear regression analysis,distribution index,transfer matrix,Theil-Sen median slope estimation and Mann-Kendall significance test to analyse the spatial and temporal variation characteristics of vegetation cover in the Chengdu-Chongqing Economic Circle.Based on related studies,ten drivers were selected and the effects of different drivers on vegetation cover changes were analysed,taking into account the actual situation of the study area.The main conclusions are as follows:(1)In terms of temporal changes,the vegetation cover changes in the Chengdu-Chongqing Economic Circle from 2000 to 2021 showed an increase in the mean maximum FVC,a decrease in the area of low-grade vegetation cover,and an increase in the area of high-grade vegetation cover.The mean annual FVC showed an increasing trend of 0.023/10 a(P<0.01),and the growth rate and significance level during 2010-2021 were smaller than those from 2000 to 2021.FVC showed a trend of significant increase(P<0.01)in all four seasons,the highest increase was observed in winter from 2000 to 2021 and from 2000 to 2021;the highest increase was observed in autumn from 2000 to 2021.(2)In terms of spatial variation,the spatial distribution of vegetation cover in the Chengdu-Chongqing Economic Circle from 2000 to 2021 showed a pattern of low in the middle and high in the fourth.The areas with higher vegetation cover were mainly distributed in Ya’an City,Leshan City,Luzhou City,Dazhou City and the southern and northeastern edges of Chongqing City,while the lower areas were mainly distributed in the main urban areas of Chengdu City and Chongqing City.In terms of spatial change trends,the vegetation changes in the Chengdu-Chongqing Economic Circle from 2000 to 2021 all showed an improving trend,with a shift from lower vegetation cover classes to higher vegetation cover classes.The vegetation in the regions of Dazhou,Chongqing,Guang’an,Leshan,Luzhou and Yibin mainly showed an improving trend,while the vegetation in the regions of Chengdu,Deyang,Meishan,Zigong and the central city of Chongqing showed a deteriorating trend.(3)Among the natural factors,the changes in average temperature and precipitation from 2000 to 2021 showed an increasing trend and showed significant positive correlation(P<0.05)with FVC in terms of time series changes,and positive and negative correlation with FVC in terms of spatial correlation by image element,respectively.Among the topographic factors,elevation and slope had a greater influence on the spatial distribution of vegetation cover.Among human activities,the night light index showed a significant increase(P<0.01)from 2000 to 2021,which was positively correlated with FVC in time series(P<0.01)and negatively correlated with FVC in image-by-image spatial correlation.negative correlations.(4)Based on the exploration of scale effects of drivers on modelling vegetation cover change,3 km was finally selected as the most appropriate grid scale.The results of the analyses at different times and regions indicate that elevation is the main natural driver of vegetation cover change,night light is the main anthropogenic driver,and the interaction between natural and anthropogenic factors has significantly increased the degree of influence on vegetation cover change.