Evaluating land-surface warming and cooling environments across urban-rural local climate zone gradients in subtropical megacities

The influence of vegetated land cover on the land surface has been extensively explored in urban environmental studies, both regionally and globally. However, addressing the challenge of surface urban heat islands (SUHI) in megacities remains complex at the landscape level because of factors such as intricate urban structures, urban-rural functions, and insufficient land surface classification for impervious surfaces. In this study, we propose a novel approach that uses Earth observation data from 2000 to 2020 to examine the warming and cooling impacts of vegetation on SUHI in the densely populated Greater Bay Area (GBA) of China. Our methodology integrates urban-rural local climate zone (LCZ) gradients with vegetation greenness modeling. Our findings highlight that dense tree coverage exhibited the most substantial cooling effect across all four seasons. Low vegetation types, such as grassland and cropland, demonstrated moderate cooling during daytime throughout the year, exhibiting slight warming during winter nights. These cooling and warming effects were consistently varied along urban-rural gradients. The SUHI tended to decrease in strength with an increase in gradient, while showing an increasing trend across downtown areas from 2000 to 2020. Extreme daytime warming was observed from 2010 to 2015, whereas extreme nighttime warming occurred between 2015 and 2020. Urban-rural and interannual changes in cooling or warming effects were more strongly associated with evapotranspiration than with albedo. Our analysis provides valuable insights for guiding local greenspace planning and combating the adverse impacts of SUHI.