Variations in Cropland Phenology in China from 1983 to 2002

In this study, we used the NDVI time-series datasets to investigate variations in the starting dates of growing season (SGS) in China's cropland from 1983 to 2002. To do so, a smoothing algorithm based on an asymmetric Gaussian function was first performed on the NDVI dataset to minimize the effects of anomalous values caused by atmospheric haze and cloud contamination. The SGS of cropland was estimated based on the smoothed NVDI time-series datasets for 1983, 1992 and 2002, respectively. The resulting three datasets were then overlaid together to calculate the changes in SGS during the period of 1983-1992 and 1992-2002. The results showed that the average date of SGS in China’s cropland over the past 20 years becomes progressively later as moving toward to the north from the south of China, corresponding well with the temperature and precipitation gradients in China. The variations of the SGS varied considerably with location and investigation period, and its general trend was characterized by a significant advance during these two periods. This study supported the conclusion by previous studies that the SGS has advanced over the past two decades at the middle and high latitudes in the northern hemisphere. Several factors can profoundly influence phenological status for cropland, such as climate change, soils and human activities. How to discriminate the impacts of biophysical forces and anthropogenic drivers on phenological events of cultivation remains a great challenge for further studies. * Corresponding author.