Temporal And Spatial Changes Of Vegetation Coverage In Southwest China Based On MODIS-EVI And Characteristics Of Its Response To Climate

As global climate change and human activities continue to intensify,the dynamic changes of surface vegetation and the response to changing environments are one of the hotspots in ecology and other fields.It is one of the important indicators for monitoring the growth of surface vegetation.It can intuitively reflect the abundance of surface vegetation.It not only provides a reliable method for analyzing the evolution of the global ecological environment,but also can be used as an assessment of regional climate change,land desertification,and regional ecological security.In this study,the southwestern region was used as the research area,and the MODIS EVI data from 2001 to 2015 was used as the basic data to study the dynamic changes of vegetation coverage,combined with the average annual precipitation and average annual temperature during this period,with the help of ENVI,Arc GIS,SPSS,MATLB and other professional software,monthly synthesis of EVI,calculation of extreme climate index,correlation analysis,trend analysis,etc.,from the three aspects of the vegetation's temporal change characteristics,spatial distribution status and spatial change trend,analyzed the vegetation coverage in southwestern China from 2001 to 2015 The characteristics of spatio-temporal dynamic changes,combined with the precipitation and temperature in the same period and the extreme climate index,explored the characteristics of the changes in the vegetation coverage changes in the southwest region and their correlations.The research indicates:(1)In the past 15 years,EVI in the southwestern region has shown a trend of fluctuating growth,with a linear growth rate of about 0.001/a.Moreover,the spatial heterogeneity of vegetation coverage in southwest China is significant,showing a gradual decreasing trend from southeast to northwest.Spatial distribution characteristics of vegetation coverage in Southwest China: High vegetation coverage is dominant,accounting for 36.1% of the total area of the study area,followed by extremely high vegetation coverage,accounting for approximately 28.7% of the total area of the study area,and low vegetation coverage The area is about 15.4% of the total area of the study area.The extremely low vegetation cover is mainly divided into 8.6% of the total area of the study area.(2)The annual average precipitation shows a trend of decreasing fluctuation at a speed of-1.34mm/a,and the annual average temperature increases at a speed of 0.02?/a.This shows that the climate in the southwestern region shows a trend of warming and drying.Moreover,the comparison shows that there is a nearly opposite relationship between precipitation and temperature trends in southwestern China.Years with high annual average temperature have low rainfall;on the contrary,years with low average annual temperature have high rainfall;especially rainfall in 2003 and 2008 The opposite relationship between quantity and temperature is most obvious.(3)From the correlation analysis of EVI with precipitation and temperature,it can be seen that EVI is mainly related to precipitation and temperature.EVI is mainly related to precipitation and temperature.The partial correlation coefficient of EVI and temperature is between-0.94-0.99,and the areas occupied by positive and negative correlation areas are 31.2% and 23.7%,respectively.The partial correlation coefficient of EVI and precipitation is between-0.93-0.96,positive The area occupied by the correlation and negative correlation areas is 22.3% and 14.8%,respectively.The partial correlation coefficient of vegetation EVI and precipitation is the highest in the northern part of the Ali region of Tibet and the central Qinghai province;the complex correlation coefficient of EVI and climatic factors is between 0-0.93 Regions with high complex correlation coefficients are mainly distributed in Naqu city of Tibet Autonomous Region,northern Ari region,Sanjiangyuan region in Qinghai province and Dazhou-Bazhong-Guangan city in Sichuan province.Regions with low complex correlation coefficients are concentrated in Tibet A few areas in the autonomous region;the area driven by climate factors in EVI is about 12% of the total area of the study area,of which the area driven by temperature and precipitation accounts for about 7% of the area of the entire study area,and the area driven by precipitation accounts for about 3.4%;the sporadic distribution of regions driven by temperature accounts for about 1.6% of the entire area.