Impact of urbanization on vegetation phenology in major cities in Yangtze River Delta region

Based on the time series NDVI images from 1998 to 2005 and by the method of moving average, the vegetation phenology in urban areas and buffer zones of Shanghai, Hangzhou, Nanjing, Changzhou, Wuxi and Suzhou in Yangtze River Delta region were calculated. The difference of average phenology in urban areas and buffer zones was analyzed, and the relationship between this difference and the distance away from urban edge was studied. The results showed that in 1998 -2005, the urbanization of the cities made the vegetations in their urban area had an earlier start of growing season (SOS), later end of growing season (EOS), longer growing season length (GSL), and smaller NDVI_amp (difference of maximal and minimal NDVI in a year). These changes were more obvious in buffer zones if they were closer to urban area. In general, urbanization made the SOS within 4 kilometers away from the urban edge started obviously earlier, and the EOS, GSL and NDVI_amp within 10 kilometers away from the urban edge changed obviously. The differences of GSL between urban and buffer zones had a significant logarithmic relationship with the distance away from the urban edge, so did the NDVI_amp.