Comparison of surface and canopy urban heat islands within megacities of eastern China

Abstract

Urban heat island (UHI) can be characterized and quantified to understand the modification of urban surfaces on the local and regional climate. This study examines UHI variation across three megacities that are located in rapid urbanization regions in eastern China (Beijing, Shanghai and Guangzhou). These cities are located within a warm temperate climate zone, north subtropical climate zone, and lower subtropical climate zone, respectively. Satellite-based land surface temperature (LST) data and air temperature records from 2003 to 2016 were used to identify surface urban heat island (SUHI) and canopy urban heat island (CUHI), respectively. Generally, the average annual SUHI is higher than the CUHI, with the greatest UHIs appearing in Beijing (SUHI: 2.33 ± 0.18 °C, CUHI: 1.45 ± 0.54 °C). UHI changes across latitudes were negatively related to humidity variation, with higher UHI in drier climates. Seasonal UHI analysis suggests that a lower SUHI would occur in winter and a higher UHI in spring and summer, except for Guangzhou. CUHI in dry season was higher than in wet season for all three megacities, and the largest CUHI (2.10 ± 0.33 °C) appeared in winter in Beijing. Various patterns of seasonal cycles of SUHI and CUHI were related to monthly precipitation and solar insolation. Annual average daytime SUHI was higher than the nighttime SUHI, and larger daytime SUHI appeared in Guangzhou, contrasting with Shanghai and Beijing. The difference between SUHI and CUHI for all seasons was also high in Guangzhou. UHI changes were considered to be altered by warm and wet conditions in mega-cities of eastern China, and heat transportation from urban surface to urban canopy provided some possible understanding of the UHI change.