Vegetation change in Yanchi of Ningxia and its relationship with climate change in recent years

Interannual variations of vegetation and its relationship with climate variables in Yanchi County of Ningxia between 1981 and 2004 were examined by using the monthly GIMMS Normalized Difference Vegetation Index (NDVI) data and local meteorological records. Overall the annual mean of NDVI increased from 1981 to 2004, and the largest increase occurred in the latest four springs. Since 1981 the area with NDVI values in the 0.2～ 0.3 category gained about 1005 km2, i.e. an increase of 14%. The annual NDVI showed a positive correlation with precipitation, surface air temperature, relative humidity and visibility respectively, and a negative correlation with evaporation. Moreover there is a significant positive correlation between spring mean precipitation and following summer, fall and annual mean NDVI, suggesting that spring rainfall is a key factor to determine the distribution of vegetation in Yanchi.