Heterogeneity of the thermal environment and its ecological evaluation in the urban region of Karaj

Temperature is one of the critical environmental parameters which is spatially heterogeneous, affecting biological, physical, and social interactions within an urban ecosystem. Therefore, the main purpose of this article is to investigate the contribution of various land covers in forming urban heat islands (UHIs) and urban cool islands (UCIs) and determining the pattern of UHI-UCI in an arid and semi-arid urbanization region of Karaj, Iran in July 2020. To achieve the goal, initially, the land surface temperature (LST) was retrieved using mono-window algorithm; maximum likelihood method was applied to generate the land cover/land use (LULC) map using Landsat 8 OLI -TIRS data. Then, the contribution index (CI) of each LULC in creating UHI and UCI was calculated. The thermal environment of the city was evaluated using Urban Thermal Field Variance Index (UTFVI). The results showed that built-up surface (0.2) and green space (0.76) contributed the most in creating UCI, while the barren cover played a major role (1.53) in creating UHI. In addition, the urban hot spots were seen in the industrial zone and bare land (adjacent to the Payam airport) in the southwest of the region. The UTFVI analysis showed that the central areas of the city (old and dense residential areas) were ecologically better as compared to the urban periphery. Therefore, it is necessary to implement mitigation strategies in the marginal areas of the study area. In general, the results of this research can be helpful in urban planning to moderate urban temperature in ecologically stressed zones.