NDVI and Regional Climate Variation Since the Implementation of Revegetation Program in Northern Shaanxi Province, China

In this paper, correlation analysis, spatial statistics, and overlay analysis have been applied to investigate the spatial patterns and temporal variations in the normalized difference vegetation index (NDVI) and analyze the relationship between NDVI and regional climate represented by the air temperature and precipitation in Northern Shaanxi Province, China, since the implementation of Returning Farmland to Forests/Grassland Project (RFFP). It has been found that the time series of annual average NDVIs have undergone three stages of temporal changes: relatively rapid increase stage from 2000 to 2002, slight fluctuation stage from 2003 to 2005, and steady increase stage from 2006 to 2010. The magnitude of NDVI changes also varies spatially. In the hilly loess area of the central and eastern regions of Northern Shaanxi Province, NDVI increased significantly; in the wind-drifting sandy area of the northern region, NDVI change was small; and in low-mountain and hilly area of the southern region, NDVI decreased slightly. Meanwhile, the precipitation had been going through a declining curve from 2000 to 2010 while the temperature was undergoing an upward trend during the same period. However, this drier-and-hotter trend has been slightly restrained over the past years. The correlation between NDVI and precipitation and temperature is positive in some areas but negative in other areas. There is no obvious linear relation among the two for the entire study area. Climate mainly impacts growth rhythm of vegetation in growth period. While the hotter summer temperature inhibits vegetation growth, the precipitation has positive but hysteretic impact on vegetation growth.