The urban heat island phenomenon is one of the major environmental consequences of rapid urbanization, the expansion of impervious surfaces, and the reduction of vegetation cover in contemporary cities. The increase in urban temperature compared with surrounding areas disrupts the thermal balance of the urban environment and causes higher energy consumption, reduced outdoor thermal comfort, intensified air pollution, and greater exposure to heat stress. This issue becomes more critical in dense urban fabrics where narrow streets, compact building patterns, extensive asphalt and concrete surfaces, limited open spaces, and insufficient vegetation increase solar radiation absorption, enhance heat storage in urban materials, reduce natural ventilation, and limit evapotranspiration. Therefore, urban thermal management and climate-responsive design have become essential strategies for improving environmental quality and thermal resilience, especially in dense urban areas.

Tabriz, as one of the major metropolitan cities in northwestern Iran, provides a suitable case for examining urban thermal behavior and evaluating the effectiveness of green space interventions. Although the city is located in a cold semi-arid climate zone, its central and compact districts experience localized heat accumulation during the warm months, particularly in summer. The dominance of built-up surfaces, limited vegetation cover, and lack of continuous green spaces in these areas contribute to the formation of urban hot spots. Accordingly, this study aims to assess the impact of green space design on reducing the intensity of urban heat islands and improving microclimatic conditions in a selected part of the central urban fabric of Tabriz.

The main research question is to determine to what extent green space design interventions can reduce air temperature, surface temperature, and pedestrian heat stress at the local scale, and how these effects vary at different heights above ground level. The innovation of this research lies in its microclimatic and design-oriented approach. Unlike many studies that focus mainly on land surface temperature, remote sensing indicators, or the general relationship between vegetation cover and urban heat islands at the city scale, this study evaluates green space as a specific design intervention at the pedestrian level. In this research, green space is considered as a combination of design measures, including shade trees, grass cover, green roofs, green walls, permeable pathways, and linear green spaces.

The research is applied and analytical in nature and was conducted through numerical simulation and scenario-based analysis. The study area is located in part of District 8 of Tabriz, around Imam Khomeini Street. This area was selected because of its high building density, high proportion of hard and impervious surfaces, limited open spaces, and lack of continuous vegetation cover. The modeled area covers approximately 200 by 200 meters and includes medium-height buildings, urban streets, asphalt and concrete surfaces, limited open spaces, and scattered vegetation.

To evaluate the impact of the intervention, two main scenarios were developed. The first scenario represents the baseline condition before intervention, in which asphalt, concrete, and other hard urban materials are dominant, while vegetation cover is limited. The second scenario represents the post-intervention condition after the implementation of green space design. In this scenario, green infrastructure elements, including shade trees, grass cover, permeable pathways, green roofs, green walls, and linear green spaces, were added to the study area. Native drought-resistant species were defined with an approximate height of 5 to 8 meters. The required input data were obtained from the Tabriz synoptic station, Google Earth Engine, urban maps, GIS data, and field surveys.

Microclimatic simulation was carried out using the three-dimensional ENVI-met model. In this study, the climatic conditions of August 2023 and the peak daytime heat period were used as the basis for simulation. The average air temperature was defined as 31.2°C, relative humidity as 37%, wind speed as 2.3 m/s, prevailing wind direction from east to west, and solar radiation as approximately 820 W/m². The main outputs of ENVI-met included air temperature, surface temperature, wind flow pattern, and the spatial distribution of hot spots at two heights: 0.5 and 3 meters above ground level.

In addition to ENVI-met simulation, selected outputs, including air temperature, relative humidity, wind speed, and radiation conditions, were entered into RayMan software to calculate the Physiologically Equivalent Temperature index before and after the intervention. This complementary analysis was used to evaluate the effect of green design not only on physical temperature reduction, but also on human thermal perception and pedestrian comfort.

The results showed that, in the baseline condition, the highest thermal concentration occurred in areas dominated by asphalt and concrete. These surfaces, due to their high capacity for absorbing solar radiation, storing heat, and lacking effective shading, created clear urban hot spots within the study area. At the height of 0.5 meters above ground level, air temperature before the intervention ranged from 30 to 32.5°C. After the implementation of the green design scenario, although the overall temperature range across the entire area did not change dramatically, spatial analysis of the simulation maps revealed a local temperature reduction of up to approximately 3°C in the intervention zones, especially near shade trees, green pathways, and permeable surfaces.

A similar pattern was observed at the height of 3 meters. Before the intervention, air temperature at this height ranged from 29.92 to 32.14°C, with the highest thermal concentration recorded along the northern and southern edges of the study area and in sections dominated by impervious surfaces and limited ventilation. After the implementation of the green infrastructure scenario, air temperature at the height of 3 meters decreased to a range of 29.71 to 31.49°C. This finding indicates that the cooling effect of the green intervention was not limited to the layer close to the ground, but also contributed to reducing heat concentration in the upper layer of the urban microclimate. However, comparison of the two heights showed that the effect of the intervention was more pronounced at 0.5 meters than at 3 meters.

In terms of surface indicators, the results revealed a considerable improvement in the thermal condition of the area after the intervention. The mean surface temperature decreased from 42.5°C in the baseline condition to 36.8°C after green design, representing a reduction of 5.7°C. At the same time, vegetation cover increased from 12% to 38%, while impervious surfaces decreased from 76% to 52%. The albedo index also increased from 0.18 to 0.31, indicating greater surface reflectivity and reduced absorption and storage of heat in urban materials. These changes show that the green intervention modified the physical properties of the urban surface, reduced heat storage capacity, improved radiative balance, and contributed to the mitigation of local thermal stress.

The complementary results obtained from RayMan confirmed the positive effect of the green intervention on pedestrian thermal comfort. The mean PET value decreased from approximately 42.7°C in the baseline condition to about 37.4°C after the design intervention, indicating an approximate 5.3°C reduction in pedestrian heat stress. This reduction was particularly significant at points that were previously exposed to direct solar radiation and hard surfaces but benefited from shading, increased vegetation cover, and reduced imperviousness after the design scenario. The consistency between ENVI-met and RayMan results demonstrates that the proposed green infrastructure intervention improved the study area both physically and in terms of human thermal perception.

Overall, the findings indicate that targeted green space design at the urban micro-scale can be an effective strategy for reducing the intensity of urban heat islands, moderating ambient temperature, decreasing surface temperature, and improving outdoor thermal comfort in the dense central fabric of Tabriz. Interventions such as planting shade trees, increasing permeable surfaces, creating green pathways, using green roofs and green walls, and reducing the share of asphalt and concrete can mitigate local urban warming by increasing evapotranspiration, creating shade, improving airflow, and enhancing surface albedo. Nevertheless, generalizing the results to the entire city of Tabriz or to other seasons requires further investigation, since this study was conducted in a micro-scale area and under the climatic conditions of August 2023. Future studies should evaluate different seasons, wind orientations, plant species, green-to-hard surface ratios, canopy density, and alternative combinations of green interventions. Despite these limitations, the results provide a practical basis for developing climate-responsive design guidelines, prioritizing interventions in urban hot spots, and enhancing thermal resilience in the dense urban fabrics of Tabriz.