Evaluating the spatiotemporal variations of daytime surface and canopy urban heat islands: an arid climate case study

Abstract

Spatiotemporal variations of surface urban heat island (SUHI) and canopy urban heat island (CUHI) are compared in this study for the arid city of Isfahan, Iran, using two datasets for land surface temperature (LST) and air temperature (AT), and three different indices: urban-rural LST difference, urban thermal field variance index (UTFVI) and urban-rural AT difference. The inverted SUHI intensity was shown to vary between −13.9 °C in summer and −1.5 °C in winter, while the hourly average CUHI intensity ranged between −4.4 °C in summer and 6.3 °C in autumn. The spatial variation of CUHI showed significant differences in UHI intensity between urban sites (p < 0.05). Based on UTFVI variation, the non-SUHI and strongest SUHI were dominant phenomena in urban sites. In contrast, SUHI intensities were negative, representing only the non-SUHI phenomenon. The correlation between SUHI and CUHI values was not significant, indicating that intensities of CUHI and corresponding SUHI are not comparable in arid climates. These results demonstrate that for arid climates, determining UHI based on UTFVI, and the urban-rural AT difference, can provide detailed information about spatiotemporal variations of UHI.