Response Of Cropland NDVI To Climatic Factors During Different Phenophases In The North China Plain

The response of vegetation growing to climate change has been a hot issue when doing climate change even global change research. North China Plain is one of the most important grain source in China. The heterogeneous responses of cropland NDVI (Normalized Difference Vegetation Index) to temperature and precipitation were analyzed using NDVI time series and station-observed climate dataduring twelve phenophasesover the North China Plain. The primary conclusions are as follows:(1) The twelve phenophases which we divided(eight for winter wheat and four for summer maize) using as time scale could clearly indicate the cropping system in the study area.(2) The lagged response of crop growing to precipitation was more noticeable than that to temperature, and NDVI was more sensitive to the precipitation (temperature) during the last and previous two phases (current and last phases).(3) The response varied with crop species and phenophases. Correlation coefficients between NDVI and precipitation were positive in most sites in the mid-late growing season (medium growing season) of winter wheat (summer maize). NDVI was also positively correlated to temperature at significance level of0.05in the early-mid growing season of winter wheat. Furthermore, NDVI was strongly related to temperature (precipitation) during germinating and turning-green (turning-green) phases. So germinating and turning-green were the phases during which crop growing was largely influenced by climatic factors in the region.(4) Spatial distribution of NDVI could be effectively used to monitor meteorology drought. Also, there was a lag when drought affected cropland. However, crop growing was significantly influenced by human activities, so crop growing was not only limited by climate factors but human factors as well, and the human activities such as irrigation could be a buffer even a correction during drought events.