Abstract:

The characters of vegetation cover change and the interaction between vegetation and atmosphere are important in geosciences and have become research focus in recent years.As a sensitive indicator of vegetation cover and vegetation growth status,the Normalized Difference Vegetation Index (NDVI) has been widely used in environmental,ecological,and agricultural studies.Climate change and human activities are both responsible for the improvement and degradation of vegetation cover to a certain degree.Especially,since the “Grain for Green Projects” was initiated by the government in 1999,it played an important role in vegetation restoration in the ecosystem vulnerable zone of Western China.Accounting for 85% of the Three Gorges Reservoir area,Chongqing municipality is an important ecological,hydrological and wildlife conservation area in Southwestern China.Examining vegetation dynamics and environmental changes in this region plays a critical role in studying the environment and ecosystems in China.We studied vegetation change and its relationship with major climatic factors in Chongqing using RS,GIS and time lag correlation methods,SPOT4 VEGETATION NDVI datasets at 1 km spatial resolution and tenday temperature and precipitation datasets between 1999 and 2010.The results are summarized as follows.Spatially averaged annual NDVI in Chongqing showed a pronounced increase during the last decade.Especially,NDVI in the Three Gorges Reservoir area increased prominently which was caused by the NDVI increase of farmland and forestland.In the Three Gorges Reservoir area,the area of NDVI decrease was concentrated around city and bank of the Yangtze River.Obviously,the reason is the increase of city and water area.By contrast,decreased NDVI outside the Three Gorges Reservoir area was mostly located in the Northwestern,Southern and Northeastern part of Chongqing.In the Northwestern part,the decrease of NDVI was caused by the vegetable base and the building of plastic bigarch Shelter.In the Northeastern and Southern part,the decrease of NDVI was caused by the construction of economic forests.Across the entire study region,both air temperature and precipitation had an influence on NDVI,but air temperature played a more prominent role.So temperature was a constraint factor for vegetation growth in Chongqing.Across the research area there were significant regional and temporal differences in the response.From southeast to northwest there were greater correlation and faster response.Different vegetation types responded to water/thermal condition differently,which was dependent on growing season and water/thermal conditions.If one certain type of vegetations growth requires a higher temperature,it will show a faster response to temperature.In contrast,if the vegetations growth do not depend so much on higher temperature,it will show a slower response to temperature.This pattern can also be applied to the response to precipitation