Vegetation phenology changes along an urban-rural gradient in Northeast China based on remote sensing

Changes of vegetation phenology along the urban-rural gradients can reflect how urbanization regulates local water and heat conditions. Remote sensing can provide vegetation phenology at large scales (e.g. regional or global), making it a great alternative to traditional observation method. Taking three provincial capital cities (Shenyang, Changchun, Harbin) in Northeast China as examples, this study examined two critical phenology parameters (start of growing season, and end of growing season) in the buffer zones within 20 km from these urban areas, which were calculated from time series MODIS NDVI images using Savitzky-Golay filtering and segmented Gaussian method. Changes of multi-year mean parameters along the urban-rural gradients in relation to land surface temperature and forest coverage were analyzed. The results show that areas closer to urban sites tend to have earlier start of growing season, later end of growing season, and greater variability. Along the urban-rural gradients, 1 °C increase of land surface temperature in spring and last winter leads to an advance in start of growing season by 6-31 days, while 1 °C increase of land surface temperature in summer and autumn leads to a delay in end of growing season by 0.9-7.6 days. In some buffer zones, increase of forest coverage also contributes similar advances in start of growing season and delays in end of growing season.