Spatial-temporal Variation In NDVI And Its Dual Response To Climate Change And Human Activities In The Three-river Basin Of Southwest China

Vegetation is an important component of terrestrial ecosystem and a sensitive indicator in the study of environment and global change.Climate and human activities are the dominant factors affecting the growth and distribution of vegetation.At the same time,the changes of surface vegetation will have corresponding feedback effects on regional climate and terrestrial system.Based on the meteorological station data,digital elevation model(DEM)data and vegetation type,using the methods of trend analysis,correlation analysis,residual analysis and partial least square(PLS),MODIS NDVI is selected as the main data source to research the spatio-temporal characteristics of NDVI and its relationship with climatic factors and human activities in the Three-river basin of southwest China(TBSC)from 2000 to 2017.The main conclusions are as follows:(1)The mean annual and growing season NDVIs in TBSC over the past 18 years showed a volatility growth trend.The average NDVIs of interannual vegetation and growing season were the highest in Lancang River Basin,followed by Jinsha River Basin,and the lowest in Nujiang River Basin.The spatial characteristics of NDVIs showed a gradually increasing trend from northwest to southeast.The interannual variation trend and rate of vegetation vary in different multiple subranges: it was found that NDVIs decreased when latitude increased from south to north,and at the same time there was an abrupt decline.The NDVIs in TBSC showed a slightly upward trend.The area of the interannual NDVI degeneration trend was larger than that of the improvement area,and the area of the NDVI trend improvement during the growing season was larger than the degradation trend area.The significance level results showed that the significantly improvement NDVI area in the study area was larger.(2)The time lag analysis of climatic factors for NDVI indicates that the NDVI had a good correlation with air temperature at the same time series and the precipitation at the previous time series.The interannual and growing season NDVIs were positively correlated with air temperature and precipitation,and the significant change area of NDVI in the growing season was larger than the interannual NDVI.(3)The interannual value of NDVI residual was between-0.013?0.016,and the trend of NDVI residual increses and fluctuates.The trend variation rate was0.9%/(10a).The growing season value of NDVI showed a slightly upward trend with a growth rate of 0.8%/(10a).The results indicated that human activities generate positive impact on the vegetation coverage in TBSC.There were distinct north-south differences among interannual and growing season variations of NDVIs residual.The regions with significantly increased annual NDVI residuals were larger than those with significantly reduced residuals,and the regions with significantly reduced annual NDVI residuals in the growth season were smaller.There were both positive effects and negative effects from the influence of human activities on vegetation change,from the spatial distribution,the area of positive effect was more than the area of negative effects overall.(4)The results of partial least squares analysis showed that the interannual and growing season NDVI were mainly affected by temperature and precipitation,and the influence of human activities was relatively small.The main influencing factors of interannual NDVI changed from north to south as precipitation changed to human activity,while the main influencing factors of growing season NDVI changed from north to south as temperature changed to human activities.