Influence of surface urban heat island on spring and autumn phenology of the forest regions in the highly urbanized Pearl River Delta, China

Abstract:

Gradients of surface urban heating affection in urban, suburban, and rural regions vary with expansion and intensification of urbanization and affect forest phenology in various ways. However, our knowledge about the association between forest phenology and land surface temperatures (LST) - and particularly its local climate zone (LCZ) variation - is still limited and needs further investigation. We tested the relationship of satellite-derived start of season and end of season metrics (SOS and EOS, respectively) with day and night LST in spring and in autumn of the forested regions integrated with LCZ in the Pearl River Delta for the period of 2000-2019. Partial Spearman's rank correlation was calculated between inter-annual SOS and day and night LST in spring and between inter-annual EOS and day and night LST in autumn in order to examine the variation of these correlations with distance to urban centers (LCZ 1: Compact and high-rise). We found SOS to have a significant negative correlation with both day LST and night LST in spring. EOS showed significant negative correlation with both day LST and night LST in autumn. The forest phenology of the urban domains (less than 2,000 m to urban centers) to be more sensitive to day LST in spring and autumn than of the suburban (between 2,000–5,000 m to urban centers) and rural regions (farther than 5,000 m to urban centers). Moreover, the areas which are sensitive to LST are more pronounced at forested areas adjoining compact and high-rise LCZ types than that adjoining open, mid- and lower-rise LCZ types. The effect of day LST on spring and autumn phenology is of equal magnitude as night LST in rural regions. We conclude that the effects of surface urban heating affection on spring and autumn phenology are more pronounced in urban than in suburban and rural zones. The results suggest that forest ecosystems adjoining compact and high-rise built-up types and less than 2,000 m to urban centers will therefore be particularly sensitive to future changes of urban heating affection and climate warming scenarios in the Pearl River Delta.