Urban design strategies for summer and winter outdoor thermal comfort in arid regions: The case of historical, contemporary and modern urban areas in Mashhad, Iran

Darbani, Elham Sanagar; Rafieian, Mojtaba; Parapari, Danial Monsefi; Guldmann, Jean‐Michel

doi:10.1016/j.scs.2022.104339

Cited by 21 publications

(11 citation statements)

References 57 publications

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“…Dense canopies have a stronger effect on blocking wind. When the wind speed is low, heat dissipation by the wind is also weak [75]. Although the wind speed in Model 1 is higher than Model 2, the mean radiation temperature and air temperature in Model 2 The tree canopy is sparse (0.225 m 2 m −3 ) in Model 1, while the tree canopy is dense (0.825 m 2 m −3 ) in Model 2.…”

Section: Resultsmentioning

confidence: 96%

A Simulation Study of the Impact of Urban Street Greening on the Thermal Comfort in Street Canyons on Hot and Cold Days

Liu,

Zheng,

Yang

2023

Forests

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The urban heat island effect has become a widely concerning issue worldwide. Many researchers have made great efforts to improve the summer thermal comfort of urban street canyons by optimizing street greening. Relatively less research has focused on how to improve the thermal comfort of street canyons by optimizing street greening during cold days. Many researchers have proposed strategies to improve the summer thermal comfort of street canyons using road greening. This may have a significant negative impact on the winter thermal comfort of street canyons due to the lack of consideration of the impact on hot and cold days simultaneously, especially when the road green space is mainly composed of evergreen tree species. We aimed to explore the impacts of urban street greening on thermal comfort on hot and cold days at the same time. We used Zhutang West Road in Changsha, China, as an example and built six different models to explore the impacts of the street vegetation types, number of street trees, tree heights, crown widths, and Leaf Area Index on the thermal comfort of the street canyon. In addition, we also considered the impact of different building features and wind directions on the thermal comfort of the street canyon. We employed ENVI-met (version 5.5.1) to simulate different urban street greening models. The results show that the model with a high tree canopy density, tall trees, large and dense crowns, and sufficient building shade has good thermal comfort on hot days (the average physiological equivalent temperature (PET) is 31.1 °C for the study period) and bad thermal comfort on cold days (the PET is 13.3 °C) when it is compared with the other models (the average PETs are 36.2 °C, 31.5 °C, 41.5 °C, 36.2 °C, and 35.5 °C, respectively, on hot days and for other models). In addition, the model with a very large number of short hedges has a positive impact on thermal comfort during hot days (the PET is 31.1 °C). The PET value of another comparable model which does not have hedges is 31.5 °C. Even if the model with a small building area has good ventilation, the small building shade area in the model has a more obvious impact and the model has relatively good thermal comfort during cold days (the PET is 14.2 °C) when it is compared to models with bigger building areas (the PET is 13.9 °C). In summer, when the wind is parallel to the direction of the street canyon, the wind speed in the street canyon is high and the model has relatively good thermal comfort (the PET is 35.5 °C) compared with another model which has different wind direction and lower wind speed at the street canyon (the PET is 36.2 °C). In winter, when the wind is perpendicular to the direction of the street canyon, buildings and trees have a strong windproof effect and this is beneficial to the improvement of thermal comfort (the PET is 15.3 °C for this model and 13.9 °C for another comparable model). This research lays a solid foundation and encourages people to think about the impact of building and tree composition and configuration on the thermal comfort of street canyons during hot and cold days simultaneously.

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Section: Resultsmentioning

confidence: 96%

A Simulation Study of the Impact of Urban Street Greening on the Thermal Comfort in Street Canyons on Hot and Cold Days

Liu,

Zheng,

Yang

2023

Forests

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“…• The width represents the mean width used throughout the main streets in Algerian desert cities. Previous studies have not recorded an aspect ratio of less than 0.5 in hot and arid climates [24,38,39,69,70].…”

Section: Defining the Selection Criteriamentioning

confidence: 96%

Effect of Street Asymmetry, Albedo, and Shading on Pedestrian Outdoor Thermal Comfort in Hot Desert Climates

Necira,

Matallah,

Bouzaher

et al. 2024

Sustainability

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Improving urban walkability in the face of climate change is a critical challenge for urban designers. Street design strategies can mitigate heat stress and enhance pedestrian livability. Most previous studies conducted in hot climates recommend adopting deep canyons to improve summer conditions, overlooking the potential improvement of wide streets as essential structural elements of the urban fabric. This study was conducted in Biskra city, southern Algeria, where several mitigation strategies were applied to ‘Emir Abdelkader Boulevard’, as the main structural street inside the city, to create an optimal street model for arid climates. Five scenarios were developed based on three criteria: (Sc1) asymmetric profile northeast side (NES) > southwest side (SWS); (Sc2) asymmetric profile SWS > NES; (Sc3) cool paving; (Sc4) horizontal shading; and(Sc5) shading with a linear tree arrangement. ENVI-met software version 5.1.1 and the RayMan model were used to estimate the local climate conditions and outdoor thermal comfort levels based on the physiological equivalent temperature (PET). All scenarios reduced PET values across the street, with optimal reductions of −2.0 °C, −3.1 °C, −1.3 °C, −1.7 °C, and −1.2 °C in Sc1, Sc2, Sc3, Sc4, and Sc5, respectively. Concerning pedestrian areas, the optimal results durations were at the southwest side below the arcades’ sidewalks during peak hours: Sc2, Sc3, Sc4, Sc5 (2.2 °C–3 H, 2.3 °C–3 H, 2.4 °C–3 H, 2.5 °C–2 H). Sc1 performed best during daytime hours on the northeast side. The utilizing of these results can strongly help urban planners and landscape architects in creating climate-responsive streets that enhance citizens’ quality of life.

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“…ΔTair is usually reported in the reviewed studies on a summer day, a typical hot day, or at a typical hot time. Some studies also compare the effects of trees during summer and winter 37,38 .…”

Section: Climate Indicators and Classification Of Meta-analysismentioning

confidence: 99%

Harnessing cooling from urban trees: Interconnecting background climates, urban morphology, and tree traits

Li,

Zhao,

Wang

et al. 2024

Preprint

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Abstract. Rapid increases in heat exposure in urban areas, fueled by both climate change and urban heat islands (UHI), are manifesting as a pressing concern. Planting and conserving urban trees is one of the pivotal strategies in mitigating outdoor heat and optimizing thermal comfort. We present an integrated review and meta-analysis of 131 studies conducted in the past 13 years, investigating the cooling effects of trees across 15 climate types in 85 global cities or regions. The cooling efficacy of trees is mainly determined by interconnecting urban morphology, tree traits, and, critically, the prevailing background climates. Our meta-analysis reveals that the cooling effects of urban trees observed in hot climates are significant due to low latitudes, along with their substantial solar radiation blockage and pronounced transpirational cooling. Moreover, an optimal level of transpirational cooling can be achieved at relatively lower humidity levels. However, in tropical and arid climates, extreme conditions involving high temperatures and vapor pressure deficits may trigger stomata closure in leaves, thereby impeding transpirational cooling. Our review further underscores the guiding principles of optimizing urban morphology by arranging buildings and trees, as well as selecting suitable tree species according to their traits to enhance the cooling effects of trees in different climates. The cooling effects of trees demonstrate a nonlinear increase in correlation with higher leaf area index (LAI), leaf area density (LAD), tree canopy coverage, and, inversely, a lower sky view factor (SVF). This systematic review and meta-analysis serve as a critical resource for researchers, urban planners, and policymakers striving to mitigate urban heat by strategically using urban trees.

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Urban design strategies for summer and winter outdoor thermal comfort in arid regions: The case of historical, contemporary and modern urban areas in Mashhad, Iran

Cited by 21 publications

References 57 publications

A Simulation Study of the Impact of Urban Street Greening on the Thermal Comfort in Street Canyons on Hot and Cold Days

A Simulation Study of the Impact of Urban Street Greening on the Thermal Comfort in Street Canyons on Hot and Cold Days

Effect of Street Asymmetry, Albedo, and Shading on Pedestrian Outdoor Thermal Comfort in Hot Desert Climates

Harnessing cooling from urban trees: Interconnecting background climates, urban morphology, and tree traits

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