Impacts of Thermal Differences in Surfacing Urban Heat Islands on Vegetation Phenology

Urbanization has significantly changed thermal environments and vegetation phenology. However, the effects of spatially different land surface temperatures (LST) on vegetation phenology, rather than differences between urban areas and rural areas, remain unclear. In this study, four cities with similar vegetation types located in temperate monsoon climate zones were selected to map vegetation phenological metrics and discuss their responses to spatially heterogeneous LST within urban areas. First, Sentinel 2-A and 2-B data were used to estimate phenological metrics by combining Savitzky–Golay filtering, and Landsat 8 TIRS data was used to obtain LST. Second, buffer zones (from the urban center to the urban edge at 1 km intervals) were used to extract the averaged phenological metrics and LST. The response of the phenological metrics to LST from the urban center to the urban edge was then analyzed. Results show that spatial differences in LST and vegetation phenology exist inside urban regions as well as between urban and peri-urban areas. In addition, the response of phenology to LST within urban areas is also obvious. SOS is negatively related to spring LST from the urban center to the urban edge, whereas EOS is positively related to autumn LST.