Spatiotemporal patterns of vegetation phenology along the urban-rural gradient in Coastal Dalian, China

Most studies on vegetation phenology along the urban-rural gradient (URG) have focused on inland cities, with a comparative lack of research on coastal cities despite their different climatic background. We used the normalized difference vegetation index (NDVI), land surface temperature (LST), and land cover data to determine spatiotemporal patterns in vegetation phenology with respect to LST along the URG in China's coastal Dalian sub-province, with a focus on the main city of Dalian and three sub-cities (Pulandian, Wafangdian, and Zhuanghe). Our results were well-correlated with MODIS Land Cover Dynamics Product (MCD12Q2) reference data and matched patterns found in previous studies, indicating that the amplitude method of TIMESAT for obtaining vegetation phenology is practical. Start of growing season (SOS) and end of growing season (EOS) of urban areas were earlier and later than rural areas, respectively. The four urban areas had dissimilar vegetation types and urbanization levels leading to different changes in SOS and EOS along the URG; the average oSOS (the difference in SOS along the URG) and oEOS (the difference in EOS along the URG) of the main and sub cities were 7.4 and 5.0 d, respectively. Changes in LST along the URG exhibited a non-linear relationship, with the maximum usually appearing 6-8 km from the urban areas. There was a strong linear relationship between vegetation phenology and LST along the URG. The winter-spring and yearly LSTs were negatively correlated with SOS, with both having roughly similar effects. The fall and yearly LSTs had significantly positive correlations with EOS, with the latter having a stronger effect. This study will be helpful for understanding climatic changes arising from urbanization in coastal areas and improving the management and productivity of the ecological environment.