Study On The Dynamic Change Of Leaf Area Index And Its Influencing Factors In Xinjiang Based On MODIS Data

This paper is based on the MODIS daily surface reflectance product(MOD15A2H,8-day composite data set with 500 m resolution),Using spatial analysis,trend analysis,correlation analysis and other methods,LAI data of xinjiang from 2000 to 2018 were studied,and the dynamic changes and driving factors of LAI in the last 19 years were discussed.At the same time,the quantitative relationship between vegetation density and evapotranspiration was further analyzed to study the spatial and temporal distribution characteristics and variation trend of surface ET of MODIS16 products in the past 19 years,and to explore the correlation between LAI and ET,DEM,temperature and precipitation.The driving analysis of LAI and climate factors on different spatial and temporal scales by remote sensing is of great value to the study of spatial distribution characteristics of vegetation,landscape pattern and the whole ecosystem in Xinjiang.The main research results are as follows:(1)The range of annual mean LAI from 2000 to 2018 is 0.31-0.49,and the annual intertemporal change of LAI has gradually increased in the past 19 years;In the changing process of seasonal time,the average LAI value in spring is 0.20,in summer is 0.65,in autumn is 0.22,and in winter is 0.06;The average LAI from January to December showed a trend of increasing first and then decreasing,and reached the highest value in July;In the process of interannual change trend,the relatively stable area accounts for the largest area,accounting for 46.58% of the total area.During the change trend process of LAI in different seasons,the relatively stable area accounted for the largest area in the change trend process of LAI in spring,accounting for 88.90% of the total area;Summer slight increase trend accounted for the largest proportion,accounting for 54.78% of the district;The relatively stable areas in autumn and winter accounted for the largest proportion,accounting for44.10% and 83.01% of the total area.(2)The interannual variation range of ET in xinjiang from 2000 to 2018 was125.01-178.14 mm,and the multi-year average was 163.08 mm.The average ET value was 96.11 mm in spring,207.85 mm in summer,57.79 mm in autumn and39.71 mm in winter.The average value of LAI from January to December showed a trend of increasing first and then decreasing,and reached the highest value in July,with the monthly average value of ET being 69.67 mm.Among the interannual ET spatial variation trends,the relatively stable region was the largest,accounting for49.67% of the total area of the whole region.In the analysis of the variation trend of different seasons,the slight increase trend in spring accounted for the largest area,accounting for 73.63% of the total area of the whole district;In summer,the relatively stable area accounted for the largest area,accounting for 32.85% of the total area;The increase trend in autumn accounted for the largest proportion,accounting for 80.94%of the total area of the district.In winter,the trend of obvious increase accounted for the largest area,accounting for 97.48 percent of the total area.(3)In the relationship between LAI and ET,the correlation coefficient between the mean value of LAI and the mean value of ET in the last 19 years is in the range of-0.85 ~ 0.99;the proportion of negative correlation area in the range of-0.85 ~ 0 is 45.48% in the whole region;the proportion of positive correlation area in the range of 0 ~ 0.99 is 54.52% in the whole region.In general,ET has a greater impact on LAI.(4)The types of vegetation cover vary with altitude.According to the actual situation in Xinjiang,the relationship between different elevations and LAI was analyzed.The area proportion of LAI in the region with an altitude of 1000 m reached the maximum,accounting for 21.87% of the area of the whole region.The mean value of LAI in the region with an altitude of 2000 m reached the maximum value,and the mean value of LAI was 0.63.(5)The temperature difference between the north and the south of Tianshan Mountain is great,and the temperature in the south is larger than that in the north,the east is larger than that in the west,the plain is larger than that in the mountain,and the center of the basin is larger than the edge of the basin.The annual precipitation on the north slope of Tianshan mountain is greater than that on the south slope.In the relationship between LAI and temperature and precipitation in the study area in the last 19 years,the correlation coefficient between average LAI and temperature ranged from-0.98 to 0.95,with the negative correlation accounting for 71.82% of the total area of the whole region and the positive correlation accounting for 28.18% of the total area of the whole region;The correlation between average LAI and precipitation ranged from-0.93 to 0.86,with the negative phase coefficient accounting for 34.40% of the total area and the positive correlation accounting for68.60% of the total area;in the partial correlation analysis,the partial correlation coefficient between temperature and LAI ranged from-0.98 to 0.915,and the partial correlation coefficient between LAI and precipitation ranged from-0.93 to 0.86.