Influence of Urban Development on the Time Series Evolution of Surface Vegetation in Xi'an Region

摘要

This Application of maximum synthesis method (MVC), regression analysis in mathematical statistics, based on time resolution of 16 days, spatial resolution of 250m MODIS_NDVI/EVI annual, seasonal and monthly vegetation index image analysis The Time Series Evolution of Vegetation in Xi'an Region from 2010 to 2016. It is opined that: 1. The trend of NDVI/EVI changes from 2013 to 2014 in Xi'an Region has a significant drop, with the rate of decline being 2.83%/a and 3.75%/a, respectively, and then rising. The growth rate of NDVI/EVI in 2014-2016 They were 3.25%/a and 3.95%/a, respectively. 2. The average monthly NDVI/EVI trend during the year in Xi'an shows a bimodal pattern, and the trend of the different phases of the monthly phase curve is similar. It can be seen that the overall NDVI/EVI changes in Xi'an during the 7 years show obvious phenological cycle changes. 3. For the same ground cover, the sensitivity of NDVI / EVI is not the same. By fitting the NDVI / EVI of the 7-month time series image of 7 years, the equation is obtained: y = 0.0556e3.0404x, R2 = 0.9511, indicating when When NDVI > 0.6, EVI is more sensitive to vegetation changes than NDVI. 5. According to the bipartite principle, the vegetation coverage of Xi'an was calculated. The results showed that the vegetation coverage in Xi'an Region has a strong regularity in spatial distribution. The high vegetation coverage area is mainly concentrated in the Qinling area south of Xi'an, and the low vegetation coverage area. Focusing on the downtown area centered on the clock tower, the contrast between the EVI and NDVI images shows that NDVI is easily saturated in high vegetation areas, and the spectral resolution of vegetation in high vegetation areas is less than that of EVI. 5. Selecting five regions of interest for block analysis, the vegetation coverage in the inner city, the second ring, and the surrounding city shows an increasing trend, and with the narrowing of the range, the growing trend becomes more obvious. The results indicate that, in the Xi'an Region, the overall changes in both NDVI and EVI are insignificant. The big reason is the effect of regional compensation, the construction of the city is saturated, the green vegetation is no longer destroyed, and along with vegetation growth and the city Greening, vegetation coverage develops in a good direction. Because the area around the county seat of HuXian County is still in the urbanization stage, the vegetation coverage in the area has been declining over time. Since there are many ecological parks located in the ecological area, the vegetation coverage in the area has fluctuating trends. The overall remains unchanged.