Response of Cropland NDVI to Climatic Factors during Different Phenophases in the North China Plain

The heterogeneous responses of cropland Normalized Difference Vegetation Index (NDVI) to temperature and precipitation were analyzed using Advanced Very High Resolution Radiometer (AVHRR) NDVI time series and station- observed climate data from 1981 to 2008 during 12 phenophases including eight for winter wheat and four for summer maize over the North China Plain. The results showed that the lagged response of NDVI to precipitation was more noticeable than that to temperature and that NDVI was more sensitive to the precipitation (temperature) during the last and previous two phases (current and last phases). Additionally, the response varied among crop species and phenophases. The correlation coefficients between NDVI and precipitation were positive at most sites in the mid-late growing season (medium growing season) of winter wheat (summer maize). NDVI was also positively correlated to temperature at the significance level of 0.05 in the early-mid growing season of winter wheat. Furthermore, NDVI was strongly related to temperature (precipitation) during germination and turning-green (turning-green) phases. Therefore, germination and turning-green were the phases during which crop growing was largely influenced by climatic factors in the region.