The Spatio-temporal Dyanmic Of NDVI In Chongqing

The growth of vegetation was influenced by many factors such as terrain, temperature, precipitation, population distribution, GDP, and urbanization, etc. Among these factors, terrain and climate are classified as natural factors which formed the overall pattern of spatial distribution of vegetation. Human factor, such as population distribution, GDP, and urbanization, would influence on local changes of vegetation. In the long run, both natural factors and human factors would drive the changes of vegetation patterns. However, in the short term, human activities would be the main driving force in the change of vegetation. Thus, the objectives of this study were to investigate the relationships between the vegetation cover and terrain, between the vegetation cover and climate, and between the vegetation cover and human factors. The results of the study would provide a guideline for regulating the environment in Chongqing.A total of 351 images of SPOT-VGTS10 with a spatial resolution of 1 km from 1998 to 2007 were used to extract normalized difference vegetation index (NDVI) for Chongqing. Several datasets, such as NDVI, climate, and human factors, were developed. Savitzky-Golay smoothing filter, maximum value composites, linear regression analysis, and time series analysis were applied to investigate the inter-annual variations of NDVI, precipitation, temperature, population, and GDP. and constructed the database of NDVI, meteorology, and human factors. The spatial distribution of NDVI and other factors were explored. The correlations between NDVI and meteorology, terrain attributes, and human factors were analyzed. The main results are as follows:(1) Clouds, aerosols and outliers could be effectively removed from the raw NDVI dataset using Savitzky-Golay filtering technology. Smoothed and filtered NDVI time series data would better reflect the presence of the vegetation coverage of Chongqing and provide the data source for studying the vegetation cover change in Chongqing. (2) The annual average NDVI and NDVI values for each year showed strong stability in Chongqing. The amount of vegetation increased yearly in Chongqing. The variations of NDVI were similar in four plantation areas, namely, northeastern, southern, central, and western Chongqing. The order of NDVI values was northeastern> southern> central> western Chongqing. The NDVI for each year showed a seasonal variation, the lowest value was found in January while the highest was in August. Moreover, the variations of inter-annual indicated that the vegetaion increase of Chongqing, especially in the western Chongqing.(3) For each county, NDVI presented strong relationship with mean temperature and weak relationship with precipitation at 10-day intervals. The spatial relationships between NDVI and climate were also investigated at seasonal scale.In spring, positive relationships were found between NDVI and precipitation and between NDVI and temperature. The area percentage of positive relations of NDVI and temperature was 72%. In summer, NDVI was positively related with precipitation in northwestern and northcentral Chongqing. Generally, NDVI showed positive relationship with temperature in the study area. However, significant negative relationships were found in western part and downtown and weak relationships existed in southeastern and southwestern regions. In autumn, NDVI was closely related with precipitation in Daba Mountain areas. NDVI showed positive relationship with temperature in eastern Chongqing and negative relationship in western Chongqing. In winter, NDVI was strongly influenced by precipitation in northeastern and southeastern regions and the correlation coefficient was negative in the north of the Yangtze River. However, the influence of temperature on NDVI in northeastern and southeastern regions was decreased compared with other seasons. NDVI of some areas was not affected by temperature, while NDVI was strongly positive related with temperature in western part.(4) Elevation showed positive relation with NDVI, especially in eastern Chongiqng. However, no relationship was found between slope and NDVI and between aspect and NDVI.(5) There was a negative correlation between maximum NDVI and population and between NDVI GDP in Chongqing, the area percentage was 51.59% and 54.39%, respectively. The integration of NDVI was nagetive related with urbanization ratio indicating the effects of urbanization on the vegetation coverage in the study area.