Spatial and temporal variation of heat islands in the main urban area of Zhengzhou under the two-way influence of urbanization and urban forestry.

Urban heat islands are major factors hindering the quality of present-day urban habitats. The ongoing acceleration of the worldwide urbanization process is leading to an exacerbation of the urban heat island effect; however, urban forestry can mitigate it. For a sustainable urban development, it is particularly important to evaluate the dual effect of both factors on the urban heat island phenomenon. In this study, we focused on Zhengzhou City (China), at the center of the Central Plains Forest City Cluster. The spatial and temporal evolutions of the local urban heat island and vegetation coverage were measured from Landsat 5 and Landsat 8 remote sensing images taken between 2006-2020 and the effects of urban construction and urban forestry on the urban heat island effect were evaluated. The results showed that, in the past 15 years, the high-temperature zone in the urban area of Zhengzhou City has gradually spread from its center to surrounding areas. Within the same period, the whole urban heat island has deteriorated and gradually improved: its area increased by 138.72 km2 between 2006-2014 and decreased by 135.66 km2 between 2014-2020. Notably, the development of vegetation coverage occurred consistently with the improvement of the heat island. A quantitative analysis of the relationship between urban construction, the urban forest, and the urban heat island has shown that factors like population density (representing urban construction), urban planning, and vegetation cover (representing the urban forest) all have an impact on the urban heat island. Based on the dynamic changes of the urban heat island in the urban area of Zhengzhou City between 2006-2020, we conclude that urban forest construction strategies are beginning to bear fruit. Overall, the findings of this study provide a theoretical basis for future urban construction and urban forest construction plans; moreover, they can support landscape pattern optimization and urban heat island mitigation.