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Article

A Comparative Study of Vegetation Strategies for Outdoor Thermal Comfort in High- and Low-Density Urban Areas

1
Department of Architecture, School of Engineering, Computing & Design, Dar Al-Hekma University, Jeddah 22246, Saudi Arabia
2
Department of Architectural Engineering, Faculty of Engineering, Aswan University, Aswan 81542, Egypt
3
Department of Architecture, University Mohamed Khider of Biskra, Biskra 07000, Algeria
*
Authors to whom correspondence should be addressed.
Urban Sci. 2025, 9(10), 416; https://doi.org/10.3390/urbansci9100416
Submission received: 28 August 2025 / Revised: 22 September 2025 / Accepted: 2 October 2025 / Published: 8 October 2025
(This article belongs to the Topic Sustainable Built Environment, 2nd Volume)

Abstract

The urban heat island (UHI) significantly compromises outdoor thermal comfort and public health in hot climates. While urban vegetation is a recognized mitigation strategy, its performance variability across different urban fabrics remains a critical knowledge gap. This research quantitatively evaluates the microclimatic impact of vegetation strategies by comparing two districts with distinct urban morphologies: low-density and high-density. Using the Envi-met software, we simulated a reference case and four vegetation scenarios with constant 50% grass coverage and incrementally increasing tree percentages (0% to 75%). Thermal performance was assessed through key metrics, including air temperature (Ta), relative humidity (RH), mean radiant temperature (Tmrt), and Physiologically Equivalent Temperature (PET). The results reveal that vegetation’s effectiveness is directly correlated with urban density. The most comprehensive strategy (Scenario-D: 50% grass, 75% trees) reduced peak PET by up to 7.5 °C in the low-density El Khazzan, a reduction nearly three times greater than the 2.7 °C achieved in the high-density El Akkad. Similarly, this scenario achieved a maximum daytime Ta reduction of 0.92 K in El Khazzan, compared to only 0.4 K in the high-density district. The study also identifies a critical trade-off: high-density tree scenarios increased nighttime temperatures by up to 0.4 K due to disrupted airflow, whereas the grass-only scenario maintained thermal stability. These findings underscore that a one-size-fits-all approach to urban greening is insufficient. For practical implications, urban planners must abandon generic strategies and integrate a nuanced understanding of local morphology to maximize the thermal benefits of vegetation, particularly in hot, arid environments.
Keywords: urban vegetation; thermal mitigation; urban morphology; microclimate; urban heat island urban vegetation; thermal mitigation; urban morphology; microclimate; urban heat island

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MDPI and ACS Style

Gomaa, M.M.; Nabil, J.; Berkouk, D.; Ragab, A. A Comparative Study of Vegetation Strategies for Outdoor Thermal Comfort in High- and Low-Density Urban Areas. Urban Sci. 2025, 9, 416. https://doi.org/10.3390/urbansci9100416

AMA Style

Gomaa MM, Nabil J, Berkouk D, Ragab A. A Comparative Study of Vegetation Strategies for Outdoor Thermal Comfort in High- and Low-Density Urban Areas. Urban Science. 2025; 9(10):416. https://doi.org/10.3390/urbansci9100416

Chicago/Turabian Style

Gomaa, Mohammed M., Jackline Nabil, Djihed Berkouk, and Ayman Ragab. 2025. "A Comparative Study of Vegetation Strategies for Outdoor Thermal Comfort in High- and Low-Density Urban Areas" Urban Science 9, no. 10: 416. https://doi.org/10.3390/urbansci9100416

APA Style

Gomaa, M. M., Nabil, J., Berkouk, D., & Ragab, A. (2025). A Comparative Study of Vegetation Strategies for Outdoor Thermal Comfort in High- and Low-Density Urban Areas. Urban Science, 9(10), 416. https://doi.org/10.3390/urbansci9100416

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