Quantification of Urban Heat Island-Induced Contribution to Advance in Spring Phenology: A Case Study in Hangzhou, China

Plant phenology is one of the key regulators of ecosystem processes, which are sensitive to environmental change. The acceleration of urbanization in recent years has produced substantial impacts on vegetation phenology over urban areas, such as the local warming induced by the urban heat island effect. However, quantitative contributions of the difference of land surface temperature (LST) between urban and rural (Delta LST) and other factors to the difference of spring phenology (i.e., the start of growing season, SOS) between urban and rural (Delta SOS) were rarely reported. Therefore, the objective of this study is to explore impacts of urbanization on SOS and distinguish corresponding contributions. Using Hangzhou, a typical subtropical metropolis, as the study area, vegetation index-based phenology data (MCD12Q2 and MYD13Q1 EVI) and land surface temperature data (MYD11A2 LST) from 2006-2018 were adopted to analyze the urban-rural gradient in phenology characteristics through buffers. Furthermore, we exploratively quantified the contributions of the Delta LST to the Delta SOS based on a temperature contribution separation model. We found that there was a negative coupling between SOS and LST in over 90% of the vegetated areas in Hangzhou. At the sample-point scale, SOS was weakly, but significantly, negatively correlated with LST at the daytime (R-2 = 0.2 and p < 0.01 in rural; R-2 = 0.14 and p < 0.05 in urban) rather than that at nighttime. Besides, the Delta SOS dominated by the Delta LST contributed more than 70% of the total Delta SOS. We hope this study could help to deepen the understanding of responses of urban ecosystem to intensive human activities.

Automated summary

This study explored the impact of urbanization on vegetation phenology in Hangzhou, with results showing that the difference in land surface temperature played a dominant role in influencing the start of growing season (SOS), contributing over 70% to the total difference in SOS between urban and rural areas.