University of Tehran Journal of Environmental Studies 1025-8620 51 1 2025 06 10 Evaluation of the Impact of Urban Form on Urban Heat Islands: A Comparative Study of Residential Areas of Mashhad, Iran Evaluation of the Impact of Urban Form on Urban Heat Islands: A Comparative Study of Residential Areas of Mashhad, Iran 97 119 102384 10.22059/jes.2025.378604.1008514 FA Fateme Mirzaeiyan 1. Department of Urban Planning, Faculty of Architecture and Urbanism, University of Ferdowsi, Mashhad, Iran Iman Ghalandarian Department of Urbanism, Faculty of Architecture and Urbanism, Ferdowsi University of Mashhad. 0000-0002-6860-2601 Maryam Talaei Department of Architecture, Faculty of Architecture and Urbanism, University of Ferdows, Mashhad, Iran 0000-0002-9428-116X Journal Article 2024 07 17 Objective: The rapid growth and expansion of urban areas have caused extensive replacement of natural land surfaces with impermeable buildings and urban materials. This process increases thermal energy absorption and results in elevated temperatures, contributing to the Urban Heat Island (UHI) effect—a significant temperature difference between urban areas and their adjacent rural regions. The primary objective of this study is to examine how different urban morphological characteristics, including spatial configuration, building height, street orientation, and urban canyon geometry, influence urban microclimatic conditions. The focus is on cold semi-arid climates, where thermal comfort is often compromised, to identify effective urban design strategies to mitigate UHI and improve outdoor thermal conditions. Method: A mixed-method research approach was adopted, involving a systematic review, morphological classification, and numerical environmental simulation. Additionally, a systematic analysis using VOS viewer software was conducted to explore the evolution of research trends related to urban form and thermal comfort, covering publications from 1973 to 2023. Subsequently, six distinct urban fabric types were selected from residential areas in Mashhad, Iran, categorized by spatial configuration (compact versus scattered) and building height classes (low-rise, mid-rise, high-rise). The microclimate of each typology was simulated using ENVI-met 5.1/6, a sophisticated 3D modelling tool that estimates variables such as air temperature, surface temperature, wind speed and direction, solar radiation, shading patterns, sky view factor (SVF), and height-to-width (H/W) ratios. Simulations were performed for three representative dates—summer solstice (June 21), winter solstice (December 21), and a moderate season (April 15), each covering a full diurnal cycle. Results: The results revealed that compact urban forms generally contributed to lower daytime air temperatures due to increased shading from dense building arrangements and higher H/W ratios. However, very compact layouts tended to reduce natural ventilation, limiting nighttime cooling. Urban canyons with low SVF reduced solar exposure during the day but trapped heat at night, decreasing overall thermal comfort after sunset. Proper alignment of streets parallel to prevailing wind directions enhanced airflow and cooling, whereas perpendicular orientations impeded ventilation. Notably, some scattered high-rise configurations created localized cooling zones due to increased wind penetration, particularly in cruciform building layouts. Conclusions: The study highlighted the importance of integrating climatic considerations into urban form design. It concluded that an optimal balance of building density, canyon geometry, and alignment with wind flow could effectively mitigate UHI impacts in cold semi-arid climates. These findings offer valuable evidence-based recommendations for urban planners and policymakers aiming to enhance thermal comfort and sustainability in rapidly urbanizing regions. Objective: The rapid growth and expansion of urban areas have caused extensive replacement of natural land surfaces with impermeable buildings and urban materials. This process increases thermal energy absorption and results in elevated temperatures, contributing to the Urban Heat Island (UHI) effect—a significant temperature difference between urban areas and their adjacent rural regions. The primary objective of this study is to examine how different urban morphological characteristics, including spatial configuration, building height, street orientation, and urban canyon geometry, influence urban microclimatic conditions. The focus is on cold semi-arid climates, where thermal comfort is often compromised, to identify effective urban design strategies to mitigate UHI and improve outdoor thermal conditions. Method: A mixed-method research approach was adopted, involving a systematic review, morphological classification, and numerical environmental simulation. Additionally, a systematic analysis using VOS viewer software was conducted to explore the evolution of research trends related to urban form and thermal comfort, covering publications from 1973 to 2023. Subsequently, six distinct urban fabric types were selected from residential areas in Mashhad, Iran, categorized by spatial configuration (compact versus scattered) and building height classes (low-rise, mid-rise, high-rise). The microclimate of each typology was simulated using ENVI-met 5.1/6, a sophisticated 3D modelling tool that estimates variables such as air temperature, surface temperature, wind speed and direction, solar radiation, shading patterns, sky view factor (SVF), and height-to-width (H/W) ratios. Simulations were performed for three representative dates—summer solstice (June 21), winter solstice (December 21), and a moderate season (April 15), each covering a full diurnal cycle. Results: The results revealed that compact urban forms generally contributed to lower daytime air temperatures due to increased shading from dense building arrangements and higher H/W ratios. However, very compact layouts tended to reduce natural ventilation, limiting nighttime cooling. Urban canyons with low SVF reduced solar exposure during the day but trapped heat at night, decreasing overall thermal comfort after sunset. Proper alignment of streets parallel to prevailing wind directions enhanced airflow and cooling, whereas perpendicular orientations impeded ventilation. Notably, some scattered high-rise configurations created localized cooling zones due to increased wind penetration, particularly in cruciform building layouts. Conclusions: The study highlighted the importance of integrating climatic considerations into urban form design. It concluded that an optimal balance of building density, canyon geometry, and alignment with wind flow could effectively mitigate UHI impacts in cold semi-arid climates. These findings offer valuable evidence-based recommendations for urban planners and policymakers aiming to enhance thermal comfort and sustainability in rapidly urbanizing regions.

https://jes.ut.ac.ir/article_102384_fd33217abbb946b4d6d2ec680acfbf5b.pdf