Authors: Xiaolin Zhu*, The Hong Kong Polytechnic University, Jiaqi Tian, The Hong Kong Polytechnic University, Zheyan Shen, The Hong Kong Polytechnic University, Shuai Xu, The Hong Kong Polytechnic University
Topics: Remote Sensing
Keywords: Urban heat island, Winter wheat, Spring phenology, Sentinel-2 time series
Session Type: Paper
Presentation File: No File Uploaded
Temperature is one of the factors controlling the phenology of winter wheat. Fast urbanization in China dramatically changes the local climate, especially raising temperature. However, it is not clear how urban landscape affects the phenology of winter wheat. To this end, this study selected three cities with different urban sizes to investigate the urban-induced microclimate effects on the winter wheat spring phenology surrounding each city using high-resolution Sentinel-2 time series. First, 20m Normalized Difference Phenology Index (NDPI) time series was generated from the Sentinel-2 images. Second, winter wheat spring re-greening phenology was extracted by the relative threshold method. Third, the relationship between winter wheat spring re-greening phenology and the urban heat island represented by nighttime land surface temperature were analyzed. Results reveal: (1) spring re-greening is earlier when closer to urbanized area. Cities with different sizes impact winter wheat re-greening to different distances, i.e., longer distance in the large city; (2) winter wheat spring re-greening phenology changes more rapidly along the urban-rural gradient in large city (0.36 day/km) than middle- and small-scale cities (0.32 day/km and 0.19 day/km), indicating that urban warming effect may decline slower towards to outskirts in large cities than small cities. This study suggests that the plantation and management of winter wheat surrounding cities should consider the influence of cities to optimize the yields.
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