关键词: 植被覆盖, NDVI, 气候因子, 人类活动, 重庆市

Abstract:

：The characters of changes of vegetation cover and the interaction between vegetation and the atmosphere is important in geosciences and has become a research focus in recent years. As a sensitive indicator of surface vegetation coverage 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 it was initiated by the government since 1999, the "Grain for Green Projects" is an important contributor to the vegetation restoration in the ecosystem fragile zone of western China. Constituting 85% of the Three Gorges Reservoir area, Chongqing City is in an important ecological, hydrological and wildlife conservation area in Southwestern China. Examining the vegetation dynamics and environmental changes over this region plays a critical role in studying the environment and ecosystems in China. Based on SPOT-4 NDVI data, the spatial and temporal changes of vegetation coverage and correlation analysis were analyzed to distinguish its relationship with temperature, precipitation and human activities. The results show that: vegetation cover changes in Chongqing showed a continued increasing during 1999-2010; vegetation cover increased rapidly during 1999-2004; vegetation cover changes came into a relative steady phase with fluctuations after that; and vegetation cover declined rapidly in drought years like 2005, 2006 and 2010. The vegetation cover changes showed a notable spatial difference. The vegetation cover has obviously increased in the Three Gorges Reservoir area and area along the Yangtze River and the Jialing River. Area of vegetation cover decreased evidently which concentrated in the drowned area of the Three Gorges Reservoir and around the city area. The spatiotemporal variations of vegetation cover are the outcome of climate factors and human activities. Temperature is a control factor of the seasonal change of vegetation growth. There are significant correlations between ten-day vegetation cover and ten-day precipitation and between ten-day vegetation cover and ten-day temperature. Thus, the changes in precipitation, especially the changes in temperature are important factors for seasonal vegetation variation. On the other side, the human factors, such as agricultural production, farmland protection and the implementation of large-scale vegetation construction, have resulted in the increase of annual NDVI and have brought some beneficial effect on ecology.

Key words: vegetation cover, NDVI, climate factors, human activities, Chongqing City