Air advection induced differences between canopy and surface heat islands

Abstract

The relationship between canopy urban heat islands (CUHIs) and surface urban heat islands (SUHIs) at four times daily temporal resolution remains unclear. The CUHI–SUHI relationship is investigated using four observations per day without temporal averaging in Shanghai, Beijing, Birmingham, and Taipei, with 201 of 2232 CUHI–SUHI pairs exhibiting significant UHI differences in their spatial distributions and intensities. These 201 UHI difference cases are determined by the correlation coefficients between air and surface temperature <0.2. The SPAtial EFficiency (SPAEF) multiple-component performance metric is applied to compare the spatiotemporal patterns of SUHIs derived from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data and CUHIs acquired from either meteorological observations or numerical simulations. The results indicate that 81.09% of the UHI differences occurred during the daytime, and were caused by local air advection related to wind speed ≥2 m/s and land surface conditions in the study areas. We conclude that joint analysis of CUHIs and SUHIs should be conducted to characterize urban thermal environments and that current urban planning procedures should integrate these UHI differences to develop effective mitigation strategies and adaptation measures.