Assessing the Potential of Revegetating Abandoned Agricultural Lands Using Nature-Based Typologies for Urban Thermal Comfort

Abstract

The rapid urbanization in developing countries has resulted in altered land-use patterns, surface energy imbalances, and heightened urban heat stress, exacerbating the urban heat island effect and vulnerability to heatwaves. The abandonment of agricultural lands, while a global challenge, presents cities with a unique opportunity to meet tree cover targets and improve resilience to these climatic challenges. Building on prior studies, this research employs the combined use of ENVI-met 4.4.6 and Ray-Man 3.1 simulation models to assess the efficacy of nature-based solutions in revegetating abandoned urban agricultural lands with the aim of enhancing outdoor thermal comfort. As a vital component of urban ecosystem services, thermal comfort, particularly through microclimate cooling, is essential for improving public health and livability in cities. This investigation focuses on the integration of broadleaf, evergreen, and edible woody species as bioclimatic interventions to mitigate urban heat stress. Simulation results showed that species such as Quercus spp. (broadleaf) and Cupressus arizonica (evergreen) substantially reduced the Mean Radiant Temperature (Tmrt) index by up to 26.76 °C, primarily due to their shading effects and large canopies. Combining these vegetation types with crops emerged as the most effective strategy to mitigate heat stress and optimize land-use. This study demonstrates how cities can incorporate nature-based solutions to adapt and mitigate the health risks posed by climate change while fostering resilience. These findings offer valuable knowledge for other developing countries facing similar challenges, highlighting the importance of revegetating abandoned urban agricultural lands for thermal comfort and ecosystem service provision, with the advantages of reducing mortality and morbidity during heatwaves. Consequently, these results should inform urban climate policies aimed at promoting resilience, public health, and ecological sustainability in a changing climate.

1. Introduction

Rapid urbanization and population growth in developing countries have significantly altered land-use patterns and disrupted the surface energy balance. These changes have intensified the urban heat island (UHI) effect and increased the frequency and severity of heat stress events in cities [1,2,3].

This phenomenon is closely linked to the degradation of green infrastructure, which has led to changes in natural topography and vegetation cover [4]. As a result, urban areas experience higher temperatures than their rural counterparts, reinforcing the UHI effect [5]. To improve thermal comfort and promote urban sustainability, it is essential to implement strategies that enhance the livability of cities for their residents [6]. In this context, nature-based solutions (NBS) offer promising approaches to address these challenges. Inspired by natural processes, NBS integrate ecological elements into urban design to restore and enhance landscapes altered by human activity [7,8]. By mitigating the environmental impacts of vegetation loss, NBS contribute to climate regulation, biodiversity enhancement, and improved public health. Crucially, they deliver key urban ecosystem services such as microclimate cooling and thermal comfort which are vital for adapting to climate change and reducing heat-related risks [9,10]. Numerous studies have demonstrated the effectiveness of NBS in addressing diverse urban challenges. For example, NBS have been shown to mitigate air pollution [11], improve stormwater management [12], and enhance ecological connectivity within cities [13]. They also contribute to microclimate regulation and the improvement of thermal comfort [14]. According to [11], nature-based planning approaches can significantly enhance human thermal comfort [7,12]. These findings emphasize the importance of embedding nature into the built environment to foster resilient, healthy, and sustainable cities.

The importance of outdoor thermal comfort in open urban areas has gained significant attention in recent decades, largely due to the dual pressures of climate change and rapid urbanization. This growing concern has led to a substantial body of research on the role of vegetation in mitigating urban heat [13]. As early as the mid-1980s, foundational studies such as the case study by [14] demonstrated that a single tree could transpire an average of 380 L of water per day. This transpiration process was found to produce a cooling effect equivalent to that of a standard room air conditioner operating for 20 h. Subsequently, ref. [15] showed that vegetation functions as a natural cooling system during summer months through the process of evapotranspiration.

More recent investigations have further emphasized the value of expanding urban green space and increasing tree cover. For instance, ref. [16] found that such practices not only enhance thermal comfort but also provide recreational and public health benefits. Ref. [17] added that the cooling and microclimatic effects of vegetation vary depending on specific plant characteristics, including canopy width, trunk height, leaf surface area, density, coloration, and foliation cycle (e.g., evergreen vs. deciduous). Similarly, refs. [18,19,20,21,22] highlighted the importance of carefully selecting tree species and employing appropriate microclimatic modeling tools in urban planning, as their physiological traits and analytical frameworks significantly influence micrometeorological conditions and contribute to local climate regulation. A recent review of 115 studies highlights consistent cooling benefits from tree canopy and mixed plantings. However, the literature reveals gaps in understanding species performance in arid zones, the influence of urban form, and responses to extreme heat [20]. Moreover, inconsistencies in temperature metrics across studies highlight the need for more standardized and context-specific research approaches [20].

These shortcomings suggest that, despite the demonstrated potential of NBS for regulating microclimates, several critical research questions remain unanswered. First, the role of abandoned agricultural land as strategic green infrastructure is still underexplored, particularly in semi-arid urban contexts where heat stress is most severe. Second, the relative cooling performance of different vegetation types—broadleaf, evergreen, and edible woody species—has not yet been systematically compared. Third, much of the existing literature continues to rely on thermal comfort indices such as Predicted Mean Vote (PMV) and Physiological Equivalent Temperature (PET), which, although widely used, fail to capture important aspects of outdoor heat stress. This underscores the need for more physiologically relevant indices, such as the Universal Thermal Climate Index (UTCI), Standard Effective Temperature (SET*), and Mean Radiant Temperature (Tmrt), especially in hot–dry climates [23,24].

Addressing these gaps requires both improved metrics and robust analytical tools capable of capturing the complex interactions between vegetation, microclimate, and human thermal perception. In this context, microclimate models such as ENVI-met and RayMan have become widely used for assessing the thermal performance of urban vegetation [19,21,22]. These tools allow researchers to simulate diverse greening scenarios, quantify thermal comfort outcomes, and evaluate the potential of green infrastructure to deliver ecosystem services in different urban settings. For example, Wang et al. (2015) [23] integrated field measurements with ENVI-met simulations to evaluate the influence of urban trees on microclimate and thermal comfort in a Dutch city. Their findings revealed that tree canopy significantly mitigates urban heat, with temperature reductions of up to 2.5 °C in shaded areas during summer. Furthermore, simulations indicated that trees improved outdoor thermal comfort by decreasing the prevalence of extreme heat stress, as measured by the Predicted Mean Vote (PMV) index.

Despite these advances, a major challenge remains: the identification and allocation of sufficient urban space for large-scale NBS implementation. High urban density and competing land-use demands often hinder local governments from achieving tree canopy targets [25]. Overcoming this obstacle requires not only technical interventions but also integrated urban planning approaches that embed green infrastructure into the broader urban fabric. In this context, abandoned agricultural land emerges as a critical and underutilized resource that can directly support efforts to expand urban tree cover. Although abandonment of agricultural land is a global issue [26,27], such land, particularly in urban and peri-urban areas, offers significant potential for revegetation and afforestation. As ref. [28] notes, these lands can be transformed through managed afforestation, ecological restoration, or spontaneous succession. These processes lead to the development of semi-natural landscapes capable of supporting tree canopy expansion. Leveraging these areas can thus contribute meaningfully to meeting municipal greening and canopy coverage goals.

Beyond canopy expansion, the benefits of restoring abandoned farmland extend further. When appropriately managed, these landscapes can improve thermal comfort for local communities [18,29] and offer additional co-benefits such as biodiversity enhancement and climate regulation. However, the ecological function and cooling potential of these areas depend on local environmental conditions, including the presence of invasive species [28]. The integration of nature-based solutions (NBS) into such areas, particularly through urban agriculture, further reinforces their multifunctional value. While urbanization has led to the decline and underutilization of agricultural land [30], these neglected spaces represent a strategic opportunity not only to increase tree canopy but also to provide vital ecosystem services and green infrastructure [31,32,33].

Revitalizing abandoned agricultural land through NBS can simultaneously support food security, enhance urban resilience, and help cities achieve critical tree cover targets [34]. Complementing these insights, several empirical studies have further examined the role of agricultural and ornamental vegetation in improving thermal comfort. A research study conducted by [35] illustrated how incorporating vegetated surfaces from urban agriculture systems can enhance building performance and human thermal comfort. Deng et al. (2023) [36] investigated the thermal comfort effects provided by trees in lower subtropical China and established a correlation between thermal comfort and Ficus altissima. Szkordilisz et al. (2016) [37] showed that vegetation, including agricultural trees, can improve indoor thermal comfort by obstructing solar radiation in Hungary. Some other studies have investigated the effect of ornamental trees on thermal comfort. For example, a study conducted by Lai et al. (2023) [38] showed that the layout of trees in a green space can affect outdoor thermal comfort by reducing air temperature, mean radiant temperature, and physiologically equivalent temperature. It has been suggested to arrange the trees downstream of the wind to avoid low winds at the site. Another study by Tochaiwat et al. (2023) [39] clarified that trees significantly enhance thermal comfort, particularly in the late afternoon when discomfort peaks. Their findings showed that trees consistently outperformed shrubs in eco-efficiency across all scenarios, with 50% tree coverage delivering the highest efficiency among the tested configurations. Expanding on these findings, ref. [4] explored nature-based agricultural systems in Tabriz, Iran. Their study highlighted the potential of integrating native plant-crop combinations to mitigate urban thermal stress. However, like many analyses relying on indices such as Predicted Mean Vote (PMV) and Physiological Equivalent Temperature (PET), their work faced limitations [4]. These indices, although valuable, can fall short in capturing the full physiological complexity of thermal perception in diverse outdoor environments [40].

To overcome these constraints and improve the precision of thermal comfort evaluation at the Tabriz site, the current study builds on the methodology of Rahimi and Nobar (2023) [4]. While their approach utilized ENVI-met with PMV and PET indices, this research advances the framework by integrating ENVI-met 4.4.6 with Ray-Man 3.1 software. This integration enables the application of more robust and widely accepted indices—Universal Thermal Climate Index (UTCI), Standard Effective Temperature (SET*), and Mean Radiant Temperature (Tmrt)—to better capture outdoor thermal comfort [38,41,42].

The novelty of this study lies in its comparative analysis of broadleaf, evergreen, and edible woody plant species, evaluated using this improved modeling approach within the unique context of Tabriz. Additionally, this research addresses a relatively overlooked issue: the ecological potential of transforming abandoned agricultural land into functional urban green spaces to improve thermal conditions. In doing so, it directly contributes to the discourse on urban heat resilience and ecological restoration [43]. Given the alarming projections by [24], which foresee a sharp rise in heat-related mortality in the MENA region under high-emissions scenarios—with Iran being especially vulnerable—this research is both timely and critical. This study seeks to fill a significant research gap by investigating how different nature-based typologies [44]—broadleaf, evergreen, and edible woody species—affect thermal comfort in abandoned urban agricultural areas in Tabriz. Specifically, it asks

• How does revegetation with different nature-based typologies influence the thermal comfort of urban dwellers in abandoned urban landscapes?
• What is the potential of abandoned urban agricultural land, once revitalized, to function as strategic green infrastructure for mitigating urban heat stress under high-density urban conditions?
• How can the revitalization of abandoned urban agricultural land contribute to improving key outdoor thermal comfort indicators such as the Universal Thermal Climate Index (UTCI), Standard Effective Temperature (SET*), and Mean Radiant Temperature (Tmrt)?

2. Materials and Methods

2.1. Study Area

This study was conducted in Hokmabad, an urban agricultural zone in Tabriz, the capital of East Azerbaijan Province, northwest Iran. Tabriz is Iran’s fourth-largest city and is situated at an elevation of 1350 m near the confluence of the Quri and Aji rivers. The region experiences a semi-arid climate, with summer temperatures ranging from 14 °C to 30 °C and winter temperatures between 5 °C and −4 °C. This area has been previously studied by [4], and the same site was selected for continuity and comparative analysis (Figure 1). Given the region’s vulnerability to climate change, as highlighted by previous studies [45], this area is expected to experience significant impacts. These include increased thermal stress, which could affect public health outcomes such as a higher risk of heat-related cardiovascular issues.

2.2. Climatic Data and Model Configuration

This research builds upon the validated ENVI-met 4.4.6 (ENVI-met GmbH, Essen, Germany) simulation framework developed by [4], which modeled microclimatic conditions in urban agricultural land using meteorological data from the East-Tabriz station on 30 June 2023. This date was identified through long-term climatic screening as a representative episode of extreme summer heat stress in Tabriz, thereby providing a rigorous basis for stress-testing vegetation scenarios. The ENVI-met V4.4.6 model was used to simulate air temperature, humidity, wind speed, and surface energy fluxes across various vegetation scenarios [4,46]. The computational domain used a horizontal grid resolution of 2 m and a vertical resolution of 1 m in the lowest layers. This allowed detailed representation of vegetation canopies, soil stratification, and built surfaces. Boundary and initial conditions were derived from observations at the nearest synoptic station (East Azerbaijan Meteorological Office), ensuring realistic forcing. The simulation domain, grid resolution, and vegetation configurations were retained to ensure consistency and comparability. Input variables included hourly air temperature, relative humidity, wind speed, and wind direction; these records were standardized and harmonized across scenarios to ensure comparability. To expand the analytical scope, this study integrates RayMan 3.1 (RayMan Project, Technische Universität Berlin, Germany) to calculate bioclimatic indices—namely, the Universal Thermal Climate Index (UTCI), Standard Effective Temperature (SET*), and Mean Radiant Temperature (Tmrt) [21,47]. RayMan 3.1 was selected for its ability to resolve shortwave, longwave, and diffuse radiative fluxes within heterogeneous urban geometries, providing accurate assessments of pedestrian-level thermal comfort. ENVI-met 4.4.6 outputs (air temperature, relative humidity, wind speed, and radiation components) were systematically imported into RayMan 3.1 for consistency in model coupling. Thermal comfort was evaluated at a reference height of 1.8 m and analyzed at 09:00 and 18:00 local time. These times represent peak outdoor activity periods and critical windows of thermal stress.

For human energy balance calculations, we assumed a reference individual: a 35-year-old male, 1.75 m tall, weighing 75 kg, with clothing insulation of 0.90 clo and a metabolic rate of 1.48 met, following established biometeorological practice [21,47].

We validated ENVI-met 4.4.6 outputs by comparing simulated air temperature and relative humidity with in situ microclimatic measurements collected at three representative points within the study area, as reported in our previous study [4,21,47]. The model showed acceptable agreement within ±1.2 °C for air temperature and ±6% for relative humidity, consistent with validation ranges reported for hot–dry urban contexts [47].

2.3. Scenario Design and Experimental Setup

This integrated framework combines site-specific microclimate modeling (ENVI-met 4.4.6) with advanced bioclimatic indices (Ray-Man 3.1) to provide a robust, reproducible basis for evaluating how revegetation and urban agriculture interventions affect pedestrian-level thermal comfort in abandoned urban landscapes (Figure 2 and Figure 3,

Table 1. Input data applied in simulation, speed at the meteorological station “East Tabriz” on 30 June 2023, in the period 10:00–18:00 LST (Adapted from [4]).

Parameter	Value
Longitude, Latitude	46°14′43″ E, 38°06′17″ N
Horizontal grid resolution	2 m × 2 m
Vertical grid resolution	2 m
Model rotation (from grid north)	16.6°
Simulation data	30 June 2023
Maximum air temperature	29.3 °C
Minimum air temperature	18 °C
Wind speed at 10 m	4.8 m/s
Wind direction	90°
Wall and Roof Material	Moderate insulation (ENVI-met default)
Soil Type	Loamy soil (agriculture)
Road Material	Asphalt

). All design scenarios were standardized with consistent environmental conditions and systematically arranged planting patterns to ensure adequate wind flow between tree canopies.

The simulations ran for eight hours, from 10:00 to 18:00, covering peak daytime thermal conditions and the highest risk of heat-related health impacts [48]. One of the hottest days of the year was deliberately chosen for the analysis. The scenarios include different combinations of NBS typologies such as trees (broadleaf, evergreen, edible), shrubs, and green vegetation to simulate various strategies (Figure 3):

• Scenario (No Vegetation): This scenario serves as the control condition where no vegetation is present. It provides a baseline for comparison to determine how various NBS typologies can influence thermal comfort in urban environments.
• Scenario A (Agricultural Land Typology): This scenario simulates the inclusion of agricultural crops.
• Scenario B1 (Broadleaf Deciduous Trees Typology): This scenario uses broadleaf deciduous trees, such as Quercus spp. as an NBS typology.
• Scenario B2 (Edible Deciduous Trees Typology): This scenario focuses on edible deciduous trees, like fruit-bearing species (e.g., apple trees).
• Scenario C1 (Evergreen Trees Typology): This scenario incorporates evergreen trees, such as Cupressus arizonica, which maintain foliage throughout the year. These trees are widely used in urban horticulture in Iran [49].
• Scenario C2 (Ornamental Conifer) This scenario represents the use of Platycladus orientalis, an ornamental conifer commonly used in Iran’s urban landscapes and for afforestation projects [50].
• Scenario E (Shrubs Typology): Selected based on their ecological adaptability, morphological characteristics, and capacity to enhance urban thermal comfort [4].

After the simulations, we compared UTCI, SET*, and Tmrt indices between the base scenario (no vegetation) and various plant-based scenarios, including combinations, to identify those that optimize thermal comfort.

2.4. Model Validation and Statistical Performance Metrics

To quantitatively evaluate the performance of each scenario relative to the baseline scenario (no vegetation), three statistical indices were calculated: the root mean squared error (RMSE), the mean absolute error (MAE), and Willmott’s index of agreement (d). These indices quantify the deviation of thermal indices (SET*, Tmrt, UTCI) in each scenario relative to the baseline scenario [4,50,51]. The formulations are as follows:

(1)

Root Mean Squared Error (RMSE):

$$\mathrm{RMSE}=\sqrt{{\displaystyle \frac{{\sum }_{i=1}^n{(Pi-Oi)}^2}{n}}}$$

(2)

Mean Absolute Error (MAE):

$$\mathrm{MAE}={\displaystyle \frac{1}{n}}\times {\sum }_{i=1}^n\left|Oi-Pi\right|$$

(3)

Willmott’s Index of Agreement (d):

$$d=1-{\displaystyle \frac{{\sum }_{n=1}^n{(\mathrm{O}\mathrm{i}-\mathrm{P}\mathrm{i})}^2}{{\sum }_{n=1}^n{\left(\left|Pi-Oi\right|+\left|Oi-Pi\right|\right)}^2}}$$

• Ō: Mean of the observed variable.
• Oi: Observed variables for each instant.
• Pi: Model-predicted variables for each instant.
• n = number of paired observations.

3. Results

The study examined various nature-based typologies to identify which plant combinations were most effective in reducing thermal indices such as UTCI, SET*, and Tmrt. The results indicated that broadleaf species (B1) and evergreen species (C1) were the most effective in reducing UTCI compared to the base scenario and Scenario A, while shrubs (E) proved to be the least effective. For Tmrt, broadleaf species (B1) and evergreen species (C1) also performed better, while coniferous species (C2) showed the least success. In terms of SET*, broadleaf species (B1) and evergreen species (C1) exhibited the highest performance, while coniferous species (C2) and shrubs (E) were the least effective. These findings suggest that nature-based typologies with large leaf areas, greater height, and broad canopies significantly improve thermal comfort. Deciduous broadleaf trees were particularly effective, outperforming evergreen species, especially during hot summer days. The combination of broadleaf species (B1) and evergreen species (C1) demonstrated substantial improvements in Tmrt, SET*, and UTCI, highlighting the benefits of integrating different nature-based typologies to enhance urban thermal comfort (Figure 4).

3.1. Universal Thermal Climate Index and Standard Effective Temperature

The results from the analysis of thermal comfort indexes, particularly the Universal Thermal Climate Index (UTCI) and Standard Effective Temperature (SET*), show that all simulated scenarios during the eight-hour simulations performed better than the base scenario. In particular, the B1 scenario (Quercus spp.) with edible deciduous trees (significantly improved the UTCI and SET* indexes when compared to the base scenario without any plants. The B1 scenario showed a reduction of 10.53 °C in UTCI and 8.55 °C in SET*, outperforming scenario A as well.

On the other hand, the B2 scenario (Malus domestica) had a weaker effect compared to B1 among edible deciduous trees. B1 performed better than B2, reducing the UTCI by 3.98 °C and the SET* index by 3.78 °C. Among evergreen trees, the C1 scenario (Cupressus arizonica) was the most effective in providing shade, resulting in a mitigation of 9.77 °C in the UTCI and 7.92 °C in the SET index compared to the base scenario. Compared to scenario A, C1 also showed a reduction of 9.3 °C in the UTCI and 7.62 °C in the SET* index. Shrubs exhibited a weaker function in mitigating thermal comfort, showing only a slight decrease of 0.4 °C in UTCI and 3.87 °C in SET from the base scenario, and a decrease of 0.07 °C in the UTCI and 3.57 °C in the SET* index from scenario A.

The average pleasant range for UTCI and SET is 17.5 °C and 23.5 °C, respectively. On the hottest day of summer, the B1 scenario showed a temperature difference of 8.83 °C in UTCI and 2.2 °C in SET, while the base scenario exhibited a larger temperature difference (Figure 5). The C1 scenario showed a temperature difference of 9.6 °C in UTCI and 2.82 °C in SET. Overall, it was observed that deciduous trees performed better than evergreen trees, with a greater reduction in both UTCI and SET indexes. Deciduous tree species caused a decline of 8.08 °C in UTCI and 6.36 °C in SET compared to scenario A (agricultural land simulation). Evergreen tree species led to a reduction of 5.17 °C in UTCI and 4.13 °C in SET. This underlines the differences in the characteristics of deciduous and evergreen trees (Figure 6).

3.2. Mean Radiant Temperature

The Tmrt simulation results show that all scenarios, including scenario A, outperformed the base scenario. Among the edible group of deciduous trees, the B1 scenario showed the highest reduction in mean radiant temperature, with 28.8 °C from the base and 27.47 °C from scenario A. The most effective shading trees were associated with C1, showing a temperature reduction of 26.76 °C compared to the base scenario and 25.43 °C compared to Scenario A. Deciduous trees (scenario B1 and B2) demonstrated a more effective process compared to evergreen trees, with an average reduction of 24.08 °C from the base scenario and 22.75 °C from scenario A. An important factor in the Tmrt component of the thermal comfort index is the presence of tree shade. The width of the canopy and the height of the tree trunks play a crucial role in this regard. Figure 7 illustrates that an increase in canopy width and trunk height leads to an improved function of reducing the Tmrt in the scenario.

3.3. Combination Scenario

The findings of this study underscore the pivotal role of integrating agricultural crops into urban agriculture systems as a strategic mechanism for land rehabilitation. Expanding upon prior research, this study employs a multi-dimensional analytical framework to investigate the synergistic effects of vegetation typology on outdoor thermal comfort through advanced bioclimatic indices. Unlike previous studies that primarily focused on temperature reduction as an isolated parameter, this research provides a more holistic assessment by examining the interactive dynamics between plant functional traits, surface energy fluxes, and human thermal perception across multiple thermal indices, including Tmrt, SET*, and UTCI. This approach distinguishes the study by offering a comprehensive understanding of vegetation-mediated microclimatic regulation.

Specifically, scenario-based simulations tailored to regional microclimatic conditions—integrating the highest-performing species (C1, B1, and A)—indicate a substantial reduction in mean radiant temperature (Tmrt) of 37.91 °C compared to the base scenario (64.58 °C), reducing Tmrt to 26.67 °C. The Standard Effective Temperature (SET*) decreased by 26.42 °C relative to the base scenario. These outcomes confirm that combining agricultural crops with broadleaf and evergreen trees produces the strongest improvements in outdoor thermal comfort. The results are summarized in Figure 8, which illustrates the relative reductions in UTCI, SET*, and Tmrt across all scenarios.

The reductions observed in UTCI, SET*, and Tmrt across revegetated scenarios can be mechanistically attributed to well-established biophysical processes that follow the conversion of abandoned agricultural land into vegetated surfaces. In unvegetated conditions (Base and A), the absence of substantial canopy cover generates high surface–atmosphere coupling, characterized by elevated sensible heat flux and reduced latent heat flux due to minimal evapotranspiration. This imbalance leads directly to higher mean radiant temperature and subsequently elevated SET* and UTCI. By contrast, vegetated scenarios (B1, C1) fundamentally alter this energy balance through three synergistic mechanisms:

• Radiative shielding—expanded leaf area index (LAI) intercepts incoming shortwave radiation, reducing direct exposure and lowering Tmrt.
• Evaporative cooling—enhanced transpiration redistributes available energy toward latent heat flux, thus reducing near-surface air temperature and alleviating thermal stress.
• Turbulent modulation—canopy height and porosity regulate airflow and convective heat dissipation, further stabilizing microclimatic conditions.

The hierarchical consistency of these processes across independent indices (UTCI, SET*, Tmrt) substantiates that the cooling effect is not a modeling artifact but a direct biophysical consequence of revegetating abandoned agricultural lands—a finding that aligns with prior experimental and modeling studies on urban vegetation–climate interactions.

Beyond isolated typologies, our final scenario integrates the most effective vegetation form with traditional agricultural crops, mirroring local planting practices. This integrative approach provides dual benefits: (i) maximizing thermal performance through synergistic canopy-crop interactions, and (ii) safeguarding the ecological productivity and continuity of peri-urban farmlands as part of the city’s strategic green infrastructure. Such integration directly operationalizes the principles of nature-based solutions (NbS), in which preserving and revitalizing urban agricultural land functions not only as a cooling intervention but also as a structural strategy to enhance ecological resilience and ensure long-term ecosystem service provision.

The statistical comparison of thermal comfort indices (SET*, Tmrt, UTCI) across scenarios relative to the baseline (No Vegetation) is presented in

Table 2. Statistical comparison of thermal comfort indices (SET*, Tmrt, UTCI) between vegetation scenarios and the baseline case.

Scenarios	SET*			Tmrt			UTCI
	RMSE	MAE	d	RMSE	MAE	d	RMSE	MAE	d
A	0.05	0.04	1.00	0.01	0.01	1.00	0.02	0.02	1.00
B1	0.10	0.08	0.98	0.29	0.25	0.76	0.23	0.17	0.89
B2	0.35	0.28	0.68	0.39	0.31	0.63	0.42	0.34	0.62
C1	0.12	0.10	0.97	0.29	0.25	0.77	0.23	0.18	0.89
C2	0.03	0.03	1.00	0.02	0.02	1.00	0.02	0.01	1.00
E	0.09	0.07	0.99	0.01	0.01	1.00	0.25	0.15	0.87
Combination (A + B1 + C1)	0.33	0.26	0.74	0.33	0.28	0.70	0.36	0.30	0.68

. Scenarios B1, B2, C1, and the combination scenario (A + B1 + C1) produced the most substantial deviations from the baseline, reflecting greater improvements in thermal comfort indices, as indicated by lower RMSE and MAE values and correspondingly lower d-values. In contrast, scenarios A (Agricultural Land), C2 (Ornamental Conifer), and E (Shrubs) remained closer to the baseline scenario, showing higher d-values and smaller deviations in RMSE and MAE, indicating relatively smaller improvements. The variation in improvement among scenarios likely reflects the differing capacities of each vegetation typology to modify microclimatic conditions and enhance thermal comfort (Table 2).

4. Discussion

4.1. Nature-Based Solution for Solving the Challenge of Climatic Discomfort

This study evaluates the potential of revegetating abandoned urban agricultural lands through nature-based solutions (NBS), with a specific focus on how different plant typologies affect thermal comfort indices (UTCI, SET*, Tmrt) A key aspect of this approach involved utilizing various scenarios that incorporated deciduous (e.g., Quercus spp.) and evergreen (e.g., Cupressus arizonica) species, evaluated through indices such as UTCI, SET*, and Tmrt. This innovative strategy not only aims to mitigate urban heat but also offers a pathway to convert abandoned agricultural lands into functional green spaces that contribute to urban tree cover and biodiversity targets. These targets are gaining momentum globally as cities face increasing pressures from climate change and urbanization. Our findings demonstrate that by strategically integrating diverse plant typologies, vacant lands can be repurposed to improve thermal comfort while also addressing broader environmental objectives such as biodiversity conservation and ecosystem service provision. This resonates with Orsini et al. (2013) [51], who emphasized the multifunctional benefits of urban agriculture for food security, biodiversity, and social inclusion in developing countries. Similarly, Posivakova et al. (2019) [52] highlighted ecological urban agriculture as a core element of sustainability, reinforcing the broader value of our proposed approach. Previous studies have not thoroughly evaluated the differential effects of various nature-based typologies on thermal comfort, revealing a significant gap in existing research. Studies such as the work by [53] have elucidated the potential of NBS in mitigating climate change risks, particularly in addressing the urban heat island effect. Other studies such as those accomplished by [54,55], applied NBS principles to face challenges associated with climate impacts. The findings of this study demonstrated that different plant species have varying effects on reducing Universal Thermal Climate Index (UTCI), Standard Effective Temperature (SET*), and Mean Radiant Temperature (Tmrt), underscoring the importance of careful plant selection in the implementation of NBS strategies. The results indicated that Quercus spp. (B1) and Cupressus arizonica (C1) performed well in terms of reducing UTCI, SET*, and Tmrt in agricultural landscapes. Furthermore, combining different tree typologies with existing vegetation proved to be an effective strategy for repurposing vacant and agricultural land to improve thermal comfort. It is crucial to note that the recommended plant species are specific to particular regions, necessitating tailored plant selection for different geographical areas. In addition, [36] examined the thermal comfort effects of Ficus altissima in a subtropical region, establishing a connection between plant species selection and thermal comfort. This research further emphasizes the complexity of implementing NBS to optimize thermal comfort in urban settings.

4.2. Insights from RayMan and ENVI-Met Simulations

ENVI-met’s recent advancements have improved the accuracy of mean radiant temperature modeling, enabling more precise evaluation of heat-mitigation strategies and resilient urban planning. Recent studies have demonstrated this improvement, highlighting the value of these models in urban thermal comfort studies [47,56]. Our study assessed the thermal comfort effects of nature-based solutions in revitalizing urban agricultural areas. RayMan simulations indicated that integrating urban agriculture crops with trees enhanced microclimatic conditions. This integration of digital simulation tools also reflects the emerging paradigm of smart urban agriculture. As Christmann et al. (2025) [57] argue, digital innovations are increasingly crucial for managing scarce urban resources and enhancing the ecological and social value of urban agriculture. Our findings contribute to this discussion by showing how simulation-based approaches can quantify the cooling benefits of combining crops with trees, thereby linking digital methods with nature-based strategies for climate adaptation. Researchers like [58,59,60] have also utilized ENVI-met and RayMan software for various scenarios, ranging from calculating thermal index models to assessing the impact of urban morphology on pedestrian thermal comfort. These studies displayed the adaptability and effectiveness of these models in understanding and improving urban thermal comfort. In the previous study by [4], the combination of deciduous and evergreen trees with crops resulted in a reduction of 1.42 in the PMV index and 5.2 °C in PET compared to the base scenario. In the present study, using an expanded set of bioclimatic indices including UTCI, SET*, and Tmrt, the same vegetation combination (B1, C1, and A) demonstrated a reduction of 10.53 °C in UTCI, 8.55 °C in SET*, and 28.8 °C in Tmrt, indicating a substantially greater cooling effect and enhanced thermal comfort when assessed through a more comprehensive modeling framework.

4.3. The Role of Vegetation in Enhancing Thermal Comfort

Previous studies have emphasized the importance of enhancing abandoned urban agricultural lands by incorporating tree cover to mitigate urban heat island effects and regulate temperature fluctuations in cities [35,61]. Our research reinforces these findings by highlighting the significant cooling effect that trees can have on abandoned agricultural lands.

Deciduous trees significantly impact thermal comfort by offering shade that reduces solar radiation reaching the ground and lowers surface temperatures [62,63]. This shading effect aids in reducing thermal stress and discomfort, particularly on sweltering summer days [37]. The presence of trees further enhances microclimate conditions by influencing air temperature and humidity, creating a more comfortable environment for pedestrians [64,65]. Variations in tree species and their morphological attributes, such as leaf area index, height, and trunk height, can impact the degree of thermal comfort improvement. Additionally, the timing of leaf fall, and defoliation can affect the shading provided by trees, with some species maintaining thermal comfort even as their canopy thins out. Overall, the inclusion of deciduous trees significantly enhances outdoor thermal comfort in urban settings. Moreover, our study revealed that crafting scenarios based on nature-based solutions (NBS) through the combination of deciduous and evergreen trees with crops can elevate people’s sense of tranquility by reducing mean radiant temperature and enhancing Universal Thermal Climate Index (UTCI) and Standard Effective Temperature (SET*). This holistic approach not only preserves agricultural lands but also prevents their conversion into urban areas. Such multifunctional benefits are consistent with Dieleman’s (2017) [66] case study of Mexico City, which demonstrated that urban agriculture contributes not only to ecological resilience but also to social inclusion and cultural identity through the preservation of traditional practices.

Prior research has illustrated the adverse impact of destroyed green infrastructure, such as agricultural lands, on the climate. Our study shows how integrating trees and crops within an NBS framework preserves the land’s original function, preventing harm and enhancing thermal comfort in the process.

Evergreen trees, although slightly less in effect compared to deciduous trees, emerge as pivotal contributors to thermal comfort in urban environments. Their ability to provide shade and reduce solar radiation leads to cooler surfaces and improved pedestrian thermal comfort, particularly during peak summer conditions [67]. Evergreen trees also play a crucial role in enhancing human thermal comfort by reducing “very hot” and “hot” thermal perceptions by approximately 16% on clear days and 11% on cloudy days [23]. Incorporating evergreen trees as a green design strategy can substantially enhance thermal comfort in outdoor spaces by shielding excessive solar radiation and offering shade [68], while our study underscores that edible trees (deciduous trees) can also provide similar benefits.

4.4. Impact on Policy and Practice

The findings of this study have practical implications for urban planning and land management in Iran and similar semi-arid regions. In cities like Tabriz, where abandoned agricultural lands are increasingly common, NBS such as revegetation using appropriate tree typologies can serve as a low-cost, climate-resilient strategy to improve thermal comfort and public health. However, implementation must consider socio-economic realities. In Iran, such projects would likely require support from municipal governments or national climate adaptation programs but could also benefit from international funding mechanisms such as carbon credits or biodiversity offset schemes. Importantly, the governance of such green spaces needs careful consideration, establishing clear responsibilities for maintenance, access, and community involvement [4]. This aligns with Christmann’s (2025) [57] findings that successful urban agriculture and nature-based initiatives require clear governance frameworks and supportive policies to balance ecological goals with social and economic realities.

Furthermore, it is vital to establish policy mechanisms for the renaturalization of abandoned spaces, not only for the thermal comfort benefits but also for the bundle of ecosystem services such an approach provides, highlighting the broader value of NBS. These mechanisms may include tax incentives for landowners to convert their land. Furthermore, when considering the use of edible trees as part of nature-based solutions, successful implementation must prioritize more sustainable approaches. While edible trees offer co-benefits like food production and community engagement, their higher maintenance demands, including pruning, pest management, irrigation, and harvesting, may limit feasibility in resource-constrained contexts. Orsini et al. (2013) [51], studying urban agriculture in developing countries, similarly emphasize that edible species can provide multiple co-benefits but require careful alignment with local socio-economic capacities and governance structures. For example, future research could explore agroecology techniques and how citizens can be involved in such projects as part of these nature-based solutions. Incorporating residents’ preferences regarding esthetics is also essential to ensure acceptance and stewardship of these NBS [44]. Beyond thermal comfort, vegetation restoration, a key component of NBS, affects multiple ecosystem services, including carbon storage and sequestration, stormwater regulation, and air quality. Therefore, a multi-criteria assessment framework is recommended to support more holistic urban ecological planning of NBS. Moreover, future research and policy efforts should explore combining carbon credits and biodiversity credits as incentives to promote the renaturalization of abandoned lands—a critical aspect of scaling up NBS.

4.5. Study Limitations and Strengths

While this study provides valuable insights into the potential of revegetating abandoned agricultural lands using nature-based typologies for urban thermal comfort, several limitations should be considered. First, the study’s simulations were conducted over a fixed 8 h period, which may not fully capture the long-term benefits of revegetation in mitigating heat. Thermal comfort in urban landscapes is influenced by daily, seasonal, and long-term variations in temperature. Future studies should consider longer simulation periods, such as 24–48 h, to better capture the full impact of revegetation strategies on thermal comfort across different times of day and year.

Second, the study was limited to a specific set of plant species and typologies chosen for the simulation. The plant species used in the simulation were a combination of naturalized plants and ornamental species commonly used in urban areas. However, the study did not include all potential species that could be considered for revegetation projects. For example, ENVI-met’s Albero tool does not list Quercus brantii, a native species in Iran, so this species was reported generically as Quercus spp. This limitation highlights the importance of incorporating native species selection into future revegetation efforts for abandoned agricultural lands, as part of a broader vision of renaturing cities and aligning with ecological restoration principles [69]. As noted by Kelt and Meserve (2016), the use of non-native species in revegetation can lead to unintended ecological consequences, and promoting plant diversity—especially through native flora—can better support native biodiversity and long-term ecosystem resilience [70].

In addition to these limitations, the study offers several important strengths. Compared to [4], which relied solely on ENVI-met and traditional indices such as PMV and PET, this research introduces an improved methodology by integrating ENVI-met with RayMan. This allows for the use of more physiologically relevant indices—UTCI, SET*, and Tmrt —providing a more comprehensive assessment of outdoor thermal comfort. Furthermore, the study addresses an underexplored context by focusing on abandoned agricultural land in a semi-arid urban environment and comparing multiple vegetation typologies.

Taken together, the findings directly address the research questions posed in the Introduction. First, the comparative analysis of vegetation typologies confirms that broadleaf and evergreen species offer superior cooling potential (RQ1). Second, the use of UTCI, SET*, and Tmrt provides a multidimensional understanding of thermal comfort across scenarios (RQ2). Third, the revegetation of abandoned agricultural land demonstrates measurable improvements in microclimate, validating its role as a nature-based solution in semi-arid urban contexts (RQ3).

5. Conclusions

Rapid urbanization has led to the loss of agricultural land and intensified urban heat stress in many cities worldwide, including Tabriz. This study evaluated nature-based solutions by revegetating abandoned agricultural lands, testing tree and shrub typologies for their effectiveness in reducing urban heat and improving microclimates. Using ENVI-met and RayMan simulations, we show that strategically combining deciduous and evergreen species significantly improves UTCI, Tmrt, and SET*.

This study is among the first to integrate ENVI-met and RayMan modeling to assess the thermal comfort benefits of revegetating abandoned agricultural lands.

Findings highlight the value of repurposing abandoned agricultural land into green infrastructure that improves thermal comfort, supports biodiversity, and enhances urban resilience Given the widespread occurrence of abandoned agricultural land, the approach is broadly transferable to other cities. Adapting species to local conditions can further mitigate urban heat and improve environmental quality.

In line with the objective of this study, namely, implementing nature-based solutions to regenerate abandoned agricultural lands, it is important to note that the findings have broader applicability beyond the local case. In the context of Iran, where many cities rely on surrounding urban and peri-urban agricultural lands as a fundamental component of green infrastructure and food supply, the revitalization of these areas carries dual benefits. On the one hand, it enhances local microclimatic conditions and mitigates urban heat stress; on the other, it secures the continuity of food production and strengthens ecological resilience. These insights highlight that strategies for ecological urban agriculture can be meaningfully extended to regions with similar socio-ecological settings worldwide. These findings provide actionable insights for policymakers, landscape architects, and urban planners, supporting the integration of nature-based solutions into land-use policies and climate adaptation strategies to enhance thermal comfort, public health, and ecological resilience in semi-arid cities. Specifically, these results inform renaturing initiatives for more resilient, biodiversity-rich cities. Future work should validate these simulation-based insights with field measurements and assess long-term co-benefits, including air quality and public health. These findings could inform urban planning, policymaking, and climate adaptation strategies, ultimately contributing to more resilient and healthier cities.