Journal of Iranian Architecture Studies

Journal of Iranian Architecture Studies

The Effect of Removing Old-Growth Trees in the Architecture of Ilam's Streets on Pedestrian Thermal Comfort Changes Based on Computational Fluid Dynamics (CFD)

Document Type : Original

Authors
karen fatahi 1
nasrin siavash 2
1 Department of Architecture, II.c., Islamic Azad University, Ilam, Iran.
2 Department of Architecture, Ilam Branch, Islamic Azad University, Ilam, Iran.
10.22052/jias.2026.259672.1591
Abstract
Vegetation, particularly old-growth trees, is a key element in regulating ambient temperature and improving citizens' thermal comfort. In this regard, the municipality of Ilam removed 160 old-growth plane trees on Khayyam (Shohada) Street to widen the street, provoking widespread reactions from citizens and environmental non-governmental organizations. The present study focuses on the microclimatic consequences of this action and analyzes its impact on pedestrian thermal comfort (PMV). The main objective of the research is to quantitatively evaluate the microclimatic changes resulting from tree removal by combining field data and Computational Fluid Dynamics (CFD) simulation. In this study, a combination of field methods and numerical simulation using ENVI-met software was employed. We collected Climatic data, including temperature, humidity, and wind speed, over 12 hours (8 AM to 7 PM) using a data logger, and modeled the area's physical and climatic characteristics under different tree-removal scenarios. For validation, the simulation results were compared with actual data, delivering high coefficients of determination for temperature (0.95), humidity (0.97), and wind speed (0.92), confirming the model's accuracy. The findings revealed that tree removal caused a 0.6-unit increase in the PMV index and a 23% decrease in pedestrian thermal comfort. In the tree-free area, asphalt surface temperature increased by up to 8°C during peak radiation hours, and surface wind speed was 20–30% higher than in the tree-covered area. Additionally, the urban heat island effect in the tree-removed zone increased effective temperature by 1.5–2 °C. These changes were especially noticeable on the western front of the street (350 m) and even negatively affected thermal comfort on the eastern front (380 m). The results indicated that removing 160 old-growth plane trees along the street generally increased the mean radiant temperature (MRT) and air temperature in the study area and shifted the pedestrian thermal comfort index (PMV) significantly toward unfavorable (warmer) conditions compared with the tree-covered area. These changes were more severe during peak heat hours (noon to afternoon) and in shaded areas, and pedestrian thermal comfort in the tree-free area exceeded the acceptable threshold. These findings emphasize the need to preserve and develop old-growth vegetation in urban planning and natural resource management.
Keywords
Thermal Comfort of Pedestrians
Old Trees
Microclimate
Urban Streets
Computational Fluid Dynamics (CFD)
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Journal of Iranian Architecture Studies
Volume 15, Issue 29
September 2026
Pages 273-294