Assessing the urban heat island variations and its influencing mechanism in metropolitan areas of Pearl River Delta, South China

Abstract

Urban heat island (UHI) is human-induced temperature reflected on the earth's surface. Although spatiotemporal variations and driving factors of UHI have been explored extensively, the underlying mechanisms of UHI remain uncertain. Using multi-source datasets of air temperature (Ta) and surface heat flux variables, we quantify the dynamics of urban-rural Ta difference (ΔT) at monthly, seasonal and annual time scales for nine cities in Pearl River Delta (PRD) during 2000–2017. The impact of sensible heat flux and latent heat flux on UHI variations are further investigated from the perspective of the surface energy balance theory. Results demonstrate that all PRD cities have apparent UHI, as evidenced by maximum ΔT in summer and minimum ΔT in winter. A notably declining trend of ΔT is observed in Shenzhen and Guangzhou, which have the largest population and build-up areas, during 2000–2017. However, trends of ΔT are not statistically significant in other cities. Attribution analysis reveals that sensible heat and latent heat significantly affect the UHI at different stages of urbanization. For the nine cities in PRD, the primary factor responsible for heat convection is the varied urban compositions formed by different developing trajectories. Specifically, sensible heat flux contributes substantially to ΔT changes in Dongguan and Shenzhen, which experienced rapid urban expansion and with complex urban structures. By contrast, latent heat flux dominates the ΔT changes in Zhongshan and Huizhou where relatively simple urban structures are preserved. Our study highlights the importance of urban patterns, sensible heat, and latent heat to understand the UHI dynamics and variations in PRD, which provides guidance for developing appropriate mitigation strategies in city planning to alleviate UHI-related burdens.