The Role of Urban Green Spaces in Mitigating the Urban Heat Island Effect: A Systematic Review from the Perspective of Types and Mechanisms

Abstract

Due to rising temperatures, energy use, and thermal discomfort, urban heat islands (UHIs) pose a serious environmental threat to urban sustainability. This systematic review synthesizes peer-reviewed literature on various forms of green infrastructure and their mechanisms for mitigating UHI effects, and the function of urban green spaces (UGSs) in reducing the impact of UHI. In connection with urban parks, green roofs, street trees, vertical greenery systems, and community gardens, important mechanisms, including shade, evapotranspiration, albedo change, and ventilation, are investigated. This study emphasizes how well these strategies work to lower city temperatures, enhance air quality, and encourage thermal comfort. For instance, the findings show that green areas, including parks, green roofs, and street trees, can lower air and surface temperatures by as much as 5 °C. However, the efficiency of cooling varies depending on plant density and spatial distribution. While green roofs and vertical greenery systems offer localized cooling in high-density urban settings, urban forests and green corridors offer thermal benefits on a larger scale. To maximize their cooling capacity and improve urban resilience to climate change, the assessment emphasizes the necessity of integrating UGS solutions into urban planning. To improve the implementation and efficacy of green spaces, future research should concentrate on policy frameworks and cutting-edge technology such as remote sensing.

1. Introduction

Global climate change and rapid urbanization have led to significant increases in urban temperatures, exacerbating the urban heat island (UHI) effect and threatening urban sustainability [1,2]. Addressing these challenges is critical for improving public health, reducing energy consumption, and enhancing environmental resilience [3]. Urban heat islands (UHIs) represent the observed temperature increase that occurs inside highly developed cities beyond their rural counterparts. Urban sustainability encounters major obstacles preventing the integration of UHI challenges since these combine to intensify thermal discomfort, energy consumption, and environmental stress [4,5,6]. Research findings show that built urban areas composed of concrete surfaces with low vegetation coverage and elevated heating devices produce this phenomenon [7,8,9]. The correlation between urban structure elements and how people interact with the environment produces joint solutions needed for effective UHI management. Thus, city planning functions as a vital solution to minimize environmental challenges and their effects.

Early research on UHIs primarily focused on documenting temperature differentials between urban and rural areas [10]. Over time, the field has advanced to include high-resolution climate modeling, remote sensing, and the integration of ecosystem services into urban planning [11,12]. Recent studies emphasize the co-benefits of green infrastructure, such as improved air quality and social connectivity, alongside thermal regulation [13,14].

The UHI effect (Figure 1) is closely linked to increased thermal discomfort, higher energy consumption for cooling, and elevated environmental stress in cities [1,2]. Several studies have demonstrated that urban areas with limited vegetation and high impervious surfaces experience greater temperature extremes, leading to increased health risks and energy demand [15].

Urban green spaces (UGSs), such as parks, green roofs, and street trees, are essential for reducing heat islands in metropolitan areas. The combined effects of water evaporation and shade provided by green spaces can lower temperatures by up to 4 °C, according to research by Aflaki et al. [16]. Additional cooling capabilities of blue-green elements can be achieved by integrating plant features with water elements, which promote evaporation and water vaporization [17,18,19]. Urban green spaces have been shown to be effective in decreasing nearby temperatures while also offering various ecological and social benefits when incorporated into city designs. The integration of UGSs in future urban planning is crucial for tackling urban heat island issues, resulting in lower energy costs, improved air quality, and enhanced thermal comfort. UGS systems play a vital role in mitigating UHI effects through their wide array of benefits that extend beyond thermal control.

Urban green spaces combat the urban heat island effect primarily through mechanisms like evaporation, shading, and increased surface reflection (albedo). The shade provided by trees and the insulation properties of green roofs minimize heat absorption in densely populated urban areas [5,20,21]. Research shows that vegetation design methods, such as layout and arrangement, directly influence the cooling capacity of urban landscapes [19,22,23]. To develop effective urban green spaces, it is essential to accurately assess tree canopy density and select vegetation for optimal performance. Various urban green spaces exhibit different capabilities in reducing the UHI effect, depending on their structural characteristics. Green roofs are particularly effective in compact city districts due to their ability to deliver localized thermal benefits and insulation [24]. The combined cooling effects, along with recreational opportunities and enhanced community well-being, make urban parks and larger green spaces perform better than others [19]. Integrating multiple UGS solutions is essential for optimal heat mitigation in cities. Urban planners can create integrated systems that maximize cooling benefits by understanding the specific advantages of various UGS types. The combination of parks, green roofs, and street vegetation forms a robust urban strategy to counter the UHI effect. Different UGS types enhance UHI mitigation because urban landscapes benefit from a variety of green infrastructure approaches.

In this context, this study aims to analyze various types of urban green spaces along with their operational mechanisms that mitigate the heat effects of urban heat islands (UHIs). This review combines research to evaluate empirical techniques and outcomes that inform practical applications. It examines the cooling abilities, scalability, and adaptability characteristics of green roofs, as well as those of urban parks and street vegetation. The investigation identifies underexplored research areas, leading to suggested directions for future investigations. A comprehensive systematic review seeks to unify fragmented research findings, enabling urban greenspace practitioners to implement these solutions more effectively across diverse urban environments. Such a thorough methodology yields conclusions that retain their relevance and strong reliability for policymakers. This review aims to establish a framework for leveraging urban green spaces (UGSs) as a practical solution to combat UHI effects, which promotes sustainable urban development.

1.1. Review Methodology

This systematic review adhered to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines to ensure methodological rigor and transparency [25]. The review focused on peer-reviewed literature from 1998 to 2024, sourced from Web of Science and Scopus, using keywords such as ‘urban heat island’, ‘urban green space’, ‘heat mitigation’, ‘green infrastructure’, ‘cooling effects’, and ‘thermal comfort’. Boolean operators (AND/OR) combined the terms to refine results.

1.1.1. PRISMA Flowchart (Figure 2) and Study Selection

The process involved four stages:

• Identification: 1238 studies were initially retrieved;
• Screening: 412 duplicates were removed, leaving 826 studies for title/abstract screening;
• Eligibility: 142 full-text articles were assessed, with 84 excluded due to irrelevance or insufficient data;
• Inclusion: 58 studies met all criteria and were retained for qualitative synthesis.

1.1.2. Inclusion Criteria

• Focus on UHI mitigation mechanisms (shading, evapotranspiration, albedo, and ventilation);
• Empirical analysis of green space types (parks, green roofs, street trees, etc.);
• Quantitative/qualitative data on cooling efficacy or urban planning implications;
• Peer-reviewed articles in English.

1.1.3. Exclusion Criteria

• Non-English studies;
• Non-peer-reviewed reports or conference abstracts;
• Studies lacking spatial/temporal resolution or contextual factors (e.g., climate zone,\ and urban density).

1.1.4. Data Extraction and Quality Assessment

Data were extracted into categories: study location, green space type, cooling mechanism, and temperature reduction. Study quality was evaluated based on the following:

• Sample size and methodological rigor;
• Clarity in reporting results;
• Relevance to UHI mitigation strategies.

This structured approach ensured a comprehensive synthesis of evidence to inform urban planning and climate resilience strategies.

2. Mechanisms of UHI Mitigation

According to previous studies, UGSs can mitigate the urban heat island effect through different mechanisms, such as shading, evapotranspiration, albedo modulation, and ventilation. These mechanisms, supported by the spatial and structural variability of greenery in the built environment, have only recently begun to be investigated in increasingly diverse research focused on the cooling capacity and additional environmental benefits of urban greenery.

2.1. Shading

One significant way urban green spaces mitigate UHIs is through shading. In this process, vegetation intercepts direct solar radiation and reduces the heat that might be absorbed by city surfaces. Areas with high vegetation, primarily characterized by a broadleaf tree species composition, can lower land surface temperatures (LST) by up to 2 °C in densely populated areas [26]. The effectiveness of street trees and large urban parks is mainly attributed to their shading function, enabling significant reductions in ground ambient air temperatures. Several studies demonstrate that urban tree shading efficiently lowers pavement surface temperatures during the day and enhances thermal comfort for pedestrians. For instance, such a study was conducted in the warm city of Los Angeles by Cheela et al. [27]. The cooling effect of shading not only positively influences the microclimate but also decreases energy consumption for air conditioning in urban buildings, thereby reducing greenhouse gas emissions linked to energy use. In a study by Jamei et al. [28], shading strategies were analyzed in terms of street orientation and building geometry, complemented by vegetation in areas of high urbanization in tropical cities. These strategies yielded remarkable temperature reductions, further decreasing the city’s energy footprint. However, it is important to note that the effectiveness of shading also relies on canopy density. Open landscapes with minimal tree cover may see little temperature reduction, emphasizing the need for strategic placement of shading structures [29]. This illustrates that shading strategies enhance urban thermal comfort and significantly contribute to reducing energy demand and, consequently, greenhouse gas (GHG) emissions in densely populated cities.

2.2. Evapotranspiration

The second primary process involves evapotranspiration by vegetation, which emits water vapor into the air while cooling the surrounding atmosphere through latent heat exchange. This process is particularly effective in urban parks and community gardens, serving as moisture reservoirs in arid urban settings. It plays an even more crucial role in regulating temperatures in subtropical megacities. Qiu et al. [30] present an evapotranspiration effect that can lower urban temperatures by a few degrees. Research findings indicate that integrating large water bodies with green spaces generates cooling effects because the combined use of evapotranspiration and shading creates extensive urban cooling, according to Jandaghian and Colombo [19]. Studies in Guangzhou, China, demonstrate that parks and community gardens produce evaporation effects that can decrease temperatures by up to 5 °C [6]. Evapotranspiration is instrumental in reducing heat in urban areas, especially when incorporating water features and plants in subtropical and arid landscapes. However, the sustainable operation of evapotranspiration relies on robust access to water resources [31]. This limitation is particularly crucial in arid cities where water resources are scarce.

2.3. Albedo Modification

Another pathway for UHI mitigation through green spaces involves albedo modification. Green roofs and walls reduce the amount of heat absorbed by buildings and other infrastructure in a city due to the increased reflectivity of their surfaces. Razzaghmanesh et al. [32] demonstrated that in urban contexts, most conventional surface types exhibit very low albedo values and very high heat storage. Therefore, in these areas, it is important to integrate green roofs that could be more intensive with diverse, dense plant cover. Green roofs and walls have enhanced surface albedo in certain cities. Additionally, temperatures as high as 2 °C have reportedly been reduced under favorable conditions, particularly in highly built-up areas like Hong Kong and Singapore [16]. In arid cities such as Phoenix, USA, reflective pavements and materials on sidewalks have been utilized to increase albedo and reduce heat gain from the surface [21]. Such developments significantly support albedo-enhancing solutions like green roofs, reflective pavements, and materials that lower urban temperatures and mitigate the UHI effect in various climatic regimes. Overall, strategies including albedo-enhancing methods such as green roofs and pavements are discussed due to their heat-non-absorbing characteristics. However, their performance is moderate compared to other environmental conditions, especially in areas where open spaces facilitate sunlight reflection, and lower population density is not readily available [33]. This limitation hinders the achievement of adequate insulation and thereby necessitates other strategies, such as shading and ventilation in such environments.

2.4. Ventilation

Ventilation is another crucial mechanism that significantly reduces the urban heat island effect. The primary contribution of green spaces to improving ventilation is their role in circulating air and distributing heat in cities. Large open areas, such as parks and green corridors, provide pathways for airflow, creating cooler air pockets and thus diminishing the intensity of heat islands. This was evident in the work of He et al. [34], where urban planning strategies incorporating ventilation corridors substantially reduced heat stress on a local scale. The study reveals that ventilation corridors have typified the reduction of locally generated heat stress by facilitating airflow along green-lined streets in cities like Tokyo, promoting thermal comfort. Moreover, incorporating water bodies into urban greenery enhances their overall cooling effect. Water features such as ponds and fountains provide supplemental evaporative cooling to increase comfort during extreme temperatures. In this context, research by Gunawardena et al. [35] noted that the efficacy of both leaf and water-related synergisms is vital for achieving substantial temperature reductions in cities. Alongside the unique landscape, incorporated water systems, like the pond–tree complex, enhance thermal flows and lower peak temperatures in various East Asian cities, such as Seoul [36]. Therefore, integrating green corridors and water bodies demonstrates how effective ventilation strategies can work together to reduce urban heat and improve thermal comfort in densely populated areas. The benefits of ventilation through green corridors and parks are also described comprehensively. However, implementing such structures requires large open spaces, which can be challenging to locate in highly developed urban areas [29]. This limitation in available space also presents an opportunity to address the challenge of integrating air exchange corridors into design solutions within existing urban planning.

Table 1. Comparison of green space mechanisms (based on the findings of existing research).

Mechanisms	Examples	Cooling Potential (°C)	Advantages	Limitations	References
Shading	Parks, Street Trees	2–3 °C	Direct solar radiation reduction	Dependent on canopy density	[2,15]
Evapotranspiration	Green Roofs, Urban Parks	2–5 °C	Humidity increase and cooling via latent heat	Needs consistent water supply	[3]
Albedo Modification	Reflective Green Walls	1–2 °C	Reduces heat absorption by surfaces	Less effective in dense urban areas	[2,3]
Ventilation	Green Corridors	Up to 3 °C	Facilitates airflow and redistributes heat	Requires large open spaces	[2,15]

illustrates various mechanisms used to combat UHIs, showcasing different mitigation strategies while highlighting their effectiveness, benefits, and limitations. Firstly, shading is primarily provided by trees in parks and vegetation along streets, which can reduce surface temperatures by an average of 2–3 °C [2,15]. However, its effectiveness is limited to a narrow area since maximum efficiency is seen in regions fully covered by a dense canopy. Therefore, spatial distribution is a crucial factor significantly affecting its performance. Secondly, evapotranspiration offers latent heat cooling, potentially decreasing temperatures by 2–5 °C, especially benefiting humid climates [3]. This is mainly facilitated by green roofs and urban parks. While this mechanism is very effective, it requires a constant water supply to maintain its performance. Thirdly, albedo modification, achieved through reflective surfaces like green walls and cool roofs, reduces heat absorption by 1–2 °C [2,3]. It is most effective in areas with high insolation but is less effective during peak urban compact periods due to insufficient circulation areas. Lastly, ventilation occurs when green corridors enhance airflow and redistribute heat, offering up to 3 °C cooling in an area [2,15]. It functions best where open space is available. Thus, the table emphasizes the strategic integration of mechanisms, each providing a unique set of benefits along with specific constraints. Combining these cooling strategies will maximize their cooling effects and address urban spatial limitations effectively.

3. Types of Urban Green Spaces

Among the most important strategies in mitigating the UHI effect are urban green spaces, which utilize various mechanisms such as shading, evapotranspiration, and increased albedo. Different green spaces, such as parks, green roofs, street trees, vertical greenery systems, community gardens, and urban forests, offer unique contributions to reducing urban temperatures and enhancing thermal comfort, as well as social and ecological benefits [See Appendix A].

3.1. Urban Parks

The inclusion of urban parks in urban developments provides several benefits. It has been found that through shading and evapotranspiration, urban parks help to manage the UHI effect significantly. Ideally, the efficiency of management measures would depend on the tree density, the number of species, and the spatial distribution of trees. In the study by Zhang et al. [2], the authors demonstrated that the most significant impacts are found in big parks with the largest and most diverse vegetation cover and a mean 9 °C decrease in LSTs. In addition, Zhang [37] examined the research in Gold Coast, Australia, which highlighted that tree density in parks was more essential for cooling than the overall size of such parks. For instance, in Xi’an, China, the cooling effects of the parks stretched as far as 241 m, influentially boosting thermal comfort in urban areas [15]. These results suggest that providing shade through trees within a park strongly mediates the effect of trees’ density and spatial arrangement on the urban park’s cooling potential. Urban green spaces are essential in urban design because they mitigate the heat island effect and heat load for better human health based on location and types of vegetation species. Although urban parks offer a significant mitigation effect of the heat island through shading and evapotranspiration, they need considerable space for the park to be most effective [29]. Such spaces may be limited in densely populated cities, implying that such designs cannot be implemented widely.

3.2. Green Roofs

The use of green roofs is essential for addressing the urban heat island effect (

Table 2. Comparative analysis of green roofs vs. conventional roofs.

Criteria	Green Roofs	Conventional Roofs	References
Urban Heat Island Effect	Significantly reduces rooftop and ambient temperatures; mitigates heat island effect	Contributes to urban heat island effect	[12,36,38]
Temperature Reduction	Can lower rooftop surface temperatures by up to 17 °C; reductions of 2–9 °C also reported	Minimal or no temperature reduction	[36,38,39]
Thermal Insulation	Provides effective thermal insulation, reducing building heat gain and energy use	Poor insulation; higher heat transfer	[12,34,36]
Energy Conservation	Reduces annual energy consumption for cooling (e.g., up to 14.5% in Singapore, 18% in Florida)	Higher energy use for cooling	[39]
Suitability for Dense Urban Areas	Highly suitable, especially where green space is limited	Less beneficial in dense urban settings	[36,38]
Cooling Efficiency Factors	Enhanced by plant type, irrigation frequency, and water features	Not applicable	[36]
Maintenance Requirements	Requires regular watering and structural support	Minimal maintenance	[33]
Design Complexity	Needs careful design for structural and load-bearing support	Simple design	[33]
Adoption Challenges	Higher due to maintenance and design needs	Widely adopted, fewer barriers	[33]

) in densely developed cities where space is limited [12]. Green roofs effectively reduce rooftop temperatures and provide thermal insulation for buildings [36]. Consequently, they are a crucial part of the urban sustainability model [12]. Wong et al. [36] revealed that green roofs implemented in buildings in Singapore and Tokyo can help lower rooftop temperatures by as much as 17 °C and serve as effective insulators. This paper demonstrates that the cooling effect can be enhanced or diminished depending on the type of plants used in rooftop gardens or their irrigation frequency. In this regard, research conducted by Han et al. [6] established that well-maintained rooftop gardens can reduce temperatures by up to 9 °F or 5 °C. Furthermore, the integration of water features may further enhance this efficiency [19]. Overall, these findings suggest that green roofs are effective in densely populated metropolises, as they contribute to thermal insulation and building energy efficiency, in addition to mitigating roof temperatures [34]. By regulating temperature and conserving energy, sustainable rooftop gardens are vital components of urban settings where large central green spaces are lacking [12]. It is widely acknowledged that green roofs lower ambient temperatures at the rooftop level while providing thermal insulating properties [36,38]. However, they require significant attention regarding watering and structural design support, which may impede widespread adoption among the public [33].

3.3. Street Trees

Street trees, planted along roads and walkways, help regulate the microclimate. For example, Wang et al. [40] showed that cooling from street trees is more effective in arid regions through the provision of shade and mitigation of heat stress for pedestrians and vehicles. Street trees improve thermal comfort, mainly in radiation through shading roads and pedestrians, by lowering LST by two degrees Celsius in arid and temperate cities [36]. For instance, in dry climates like Phoenix, USA, street trees shield residents and motorists from direct sun and decrease air temperatures [21]. The result is even more significant if combined with reflective pavements to increase albedo and decrease the heat island effect [41]. This suggests that location, as well as tree type, plays a critical role in the cooling effect of the trees. Based on the existing research, the best outcomes are when trees are planted with a high albedo pavement and good irrigation. The analysis showed that street trees help improve comfort for pedestrians and lower the surface temperature. However, their cooling effect depends on the species and the density of the canopy cover, and they apply to sidewalks and streets only and not to whole cities [42]. Overall, street trees are functional and possible as a method of UHI alleviation at a micro-scale, especially in conjunction with other sustainable urban materials such as high albedo pavements.

3.4. Vertical Greenery Systems

Vertical greenery systems, such as green walls, have been increasingly adopted in high-density urban areas where constraints limit traditional green spaces. These systems mitigate urban heat islands (UHIs) through shading and evapotranspiration, while also enhancing aesthetic appeal and air quality in urban settings [43]. They can lower surface temperatures by 0.5 to 2.0 °C and contribute to improvements in beauty and air cleanliness [16]. Overall, vertical greenery has proven remarkably beneficial in controlling solar heat gain on building envelopes in Hong Kong [44]. When combined with rooftop greenery, these systems create a cooling network that integrates functions to mitigate heat island effects. Vertical greenery systems are particularly suited for high-rise buildings, as they help reduce facade temperatures and improve air quality while being readily applicable to the existing urban environment. Thus, this serves as another flexible solution for cooling in densely populated areas, simultaneously providing ecological and aesthetic benefits.

3.5. Community Gardens

Community gardens integrate urban agriculture and cooling mechanisms that foster social cohesion and mitigate UHIs. Their multifunctionality enables the incorporation of ecological, social, and climatic benefits into a sustainable aspect of urban design [45]. Moreover, their cooling potential increases with plant cover and humidity, as demonstrated in Los Angeles [46]. Community gardens offer localized cooling through shading and evapotranspiration. However, they often remain limited in scale and primarily benefit their immediate environment rather than contributing to city-wide cooling [29]. Along with the engagement of the local community and the integration of ecological approaches to the issue, community gardens effectively address UHI through various co-benefits related to environmental and social contexts.

3.6. Urban Forests and Green Corridors

Other innovative approaches in developing urban forests and green corridors enhance connectivity among green spaces and amplify their cumulative cooling effects across the broader cityscape [11]. Green zones, also known as urban woods and green strips, increase overall mitigative benefits by interconnecting small patches of greenery and improving air movement. Specifically, connected green spaces in Kuala Lumpur reduced temperatures by 4 °C due to the combined effects of shading and ventilation [16]. In Tokyo, green corridors help redistribute heat, addressing thermal inequality throughout the city [34]. The green belts and corridors within a city enhance aerodynamic balance, promoting air movement and linking several small green areas to significantly impact city temperature. These two elements of sustainable city planning expand cooling across entire urban regions by connecting isolated areas of green infrastructure.

Table 3. Comparison between the types of urban green spaces (based on the findings of existing research).

Types of Urban Green Spaces	Cooling Mechanism	Cooling Potential (°C)	Advantages	Limitations	References
Urban Parks	Shading, Evapotranspiration, Ventilation	2–5 °C	Large-scale cooling, improved biodiversity, recreational value	Requires large areas, dependent on tree density and species diversity	[15,29,37,47]
Green Roofs	Shading, Evapotranspiration, Albedo Modification	1–3 °C	Space-efficient, improves rooftop insulation, reduces energy demand	High maintenance, water demand	[6,12,19,33,34,36,38]
Street Trees	Shading, Ventilation	2–3 °C	Localized cooling, enhances pedestrian comfort, reduces road temperatures	Dependent on tree species and canopy density, limited to street coverage	[21,36,40,41,48]
Vertical Greenery Systems	Shading, Evapotranspiration	0.5–2 °C	Applicable to high-density areas, enhances aesthetic appeal and air quality	Limited temperature reduction, dependent on species and maintenance	[16,43,44]

underlines that urban green has manifold potential in UHI mitigation and that evidence shows that it represents one of the most significant contributions to building city resilience. Ecological, technological, and design innovation will be required during the development of cities to incorporate the full use of green infrastructure potential for the problems caused by urban heat.

4. Interaction and Correlation Among Mechanisms and Types of Urban Green Spaces

Urban green spaces counteract the urban heat island effect by using several mitigation mechanisms, such as shading, evapotranspiration, variation in albedo, or ventilation. These different mechanisms interact in various ways within green parks, roofs, street trees, and vertical gardens. Understanding their interrelation leads to insights that allow for more targeted and effective city planning.

4.1. Comparing Cooling Effects of Control Variables

The structured control variable methodology will enable segregated quantitative observation and understanding of the effects that well-defined mechanisms have on various types of green spaces in an urban environment (

Table 4. Summary of cooling effects of urban green space types across mechanisms.

Mechanism	Urban Parks	Green Roofs	Street Trees	Vertical Greenery Systems	Community Gardens	Urban Forests and Green Corridors
Shading	Large-scale shading; reduces air temperatures by up to 5 °C	Localized shading; reduces rooftop temperatures by 1–2 °C	Enhances pedestrian comfort by reducing pavement temperatures by 2–3 °C	Provides facade shading; reduces surface temperatures by up to 11.6 °C	Limited shading benefits in compact spaces	Extensive shading coverage; mitigates heat at regional scale
Evapotranspiration	Large-scale cooling; reduces air temperatures by up to 5 °C	Localized cooling through vegetation; reduces rooftop temperatures by up to 4 °C	Moderate cooling through combined shading and evapotranspiration	Enhances localized evapotranspiration and reduces facade heat	High evapotranspiration; reduces air temperatures by 2–3 °C	Broad-scale cooling through dense vegetation
Albedo Modification	Moderate reflectivity combined with shading	High reflectivity; reduces rooftop temperatures by up to 2 °C	Reflective benefits combined with shading effects	High reflectivity combined with vertical shading	Reflective materials integrated with garden layouts reduce temperatures by 2 °C	Enhances urban albedo; reduces peak temperatures by 3 °C
Ventilation	Facilitates natural airflow; enhances city-wide cooling	Improves rooftop airflow; localized ventilation	Enhances pedestrian-level airflow and thermal comfort	Reduces facade heat and improves localized airflow	Enhances microclimatic ventilation in urban areas	Facilitates large-scale airflow; reduces UHI effects by up to 2 °C

). The performance of various green space types is assessed by fixing a cooling mechanism. This will be done by understanding the performances concerning mechanisms such as evapotranspiration or shadowing across different types of green infrastructure under similar conditions. Through this method, it is possible to isolate the effectiveness of specific types, thus allowing targeted urban planning interventions.

4.1.1. Shading

Shading directly impinges on urban surfaces and leads to decreased solar radiation absorption and reduced urban surface heat accumulation. Variations in shading effectiveness specific to different types of green spaces are observed.

Urban Parks vs. Green Roofs

Urban parks provide shading where canopy cover spans areas as large as 1 km². This shading mechanism reduces surface temperatures in suburban areas [35]. For instance, urban parks and tree canopy programs in New York, like MillionTreesNYC, have significantly lowered urban temperatures by 2–3 °C through shading (Shishegar, N., 2015) [24]. Additionally, Sydney, Rahman et al. [42] found that incorporating shading structures with existing urban parks can decrease ground-level temperatures by up to 3 °C during peak summer hours, particularly in areas frequented by pedestrians. Conversely, green roofs offer localized shading advantages, especially in densely populated urban centers. For example, green roofs in Berlin were shown to reduce temperatures by 1.5 °C in the summer [49]. Moreover, green roofs utilized in Singapore’s commercial zones have been found to lower surface temperatures by up to 2.5 °C, making them suitable for compact, high-density urban settings [50]. Strategically combining these types of green infrastructure can enhance shading effects, thereby significantly reducing urban temperatures and improving thermal comfort in diverse urban settings.

Urban Parks vs. Street Trees

Street trees are valuable contributors to shading roads and pedestrian pathways. Their presence can lower surface temperatures by 2–3 °C, which is a significant difference in arid zones [40]. The shading effect of street trees is influenced by the tree species, canopy density, and their location. A large canopy provides a much larger shaded area but occupies more space and requires regular maintenance. Street trees are ideal for mitigating localized heat stress on the ground in dense urban corridors and areas with high pedestrian activity [43]. Studies in Hong Kong have indicated that a high cover of street tree canopies can effectively reduce daytime air temperatures more than low-density vegetation in parks, achieving cooling of up to 1.5 °C during the summer [51]. In Melbourne, research found that tree-lined streets averaged a 1.5 °C reduction in summer peak radiation heat load and shade for pedestrians [52]. This highlights the significance of canopy density on the cooling effects in urban streets.

On the other hand, urban parks are usually a combination of tree canopies, shrubs, and grass, which allows for extensive shading over a large area. Spronken-Smith and Oke [10] concluded that urban parks reduced air temperatures by 1–2 °C in Vancouver, and larger urban parks decreased them by up to 5 °C over adjacent urbanized areas. The cooling power of contiguous shaded zones in parks is underscored. Olympic Park in Beijing, which includes tree clusters and open green spaces in an urban area, reduced air temperatures by 0.5–1.1 °C in summer, and street trees in adjacent areas reduced pavement temperatures by up to 15.2 °C [53]. These examples demonstrate that urban parks provide substantial chilling benefits with their large dimension. However, street trees still perform best in improving localized pedestrian comfort by providing direct shading of heat-absorbing surfaces like roads and sidewalks. Thus, the synergistic strategy for reducing urban heat can combine large parks to cool the entire city with dense street tree canopies that modulate temperatures in a patchwork pattern.

Green Roofs vs. Vertical Greenery Systems

Vertical greenery systems (VGSs) and green roofs offer innovative solutions for urban greening, each employing different mechanisms to reduce temperatures and potentially providing complementary benefits in lowering urban heat. Vertical greenery systems excel at shading building facades. For instance, VGS installations in Vienna lowered building surface temperatures by up to 11.6 °C compared to conventional public spaces, effectively reducing thermal load during peak summer months [54]. Similar results have been observed in Singapore, where green walls have decreased facade temperatures by 2.5 °C [50]. Additionally, a study in Beijing revealed that vertical greenery systems enhanced thermal comfort by diminishing radiant heat exposure, especially in densely built areas. While facade cooling is a significant advantage of these systems, they require maintenance and irrigation, raising concerns about their scalability in arid climates.

Conversely, green roofs cool rooftops through a combination of shading, evapotranspiration, and albedo modification. In Tokyo, green roofs lowered rooftop temperatures by 1–2 °C and improved building insulation, resulting in energy savings of up to 20 percent for energy users [32]. In Melbourne, green roofs featuring Sedum vegetation achieved reductions in rooftop temperatures of up to 5 °C and showed particular effectiveness under sunny conditions, although additional irrigation greatly improved performance [52]. These results emphasize the significance of vegetation type and watering strategies in enhancing green roof performance. Moreover, green roofs that cover 25–100 percent of urban rooftop areas have been shown to decrease daytime roof temperatures by up to 3 °C in Chicago, with variations based on coverage and urban density [33]. However, the limited vertical extent of green roofs restricts their effectiveness in cooling building facades.

In summary, vertical greenery systems and green roofs address different urban cooling requirements. Green roofs are more adept at managing heat on rooftops and enhancing energy efficiency, while VGSs excel at lowering facade temperatures in high-risk areas. The choice between these solutions should be guided by site-specific configurations and cooling priorities.

Urban Forests and Green Corridors vs. Community Gardens

Community Gardens can offer significant but localized cooling benefits compared to the extensive cooling benefits of urban forests and green corridors by using extensive vegetation compared to the traditional community gardens’ approach to microclimate improvements. Overall, they give extensive shading coverage, which reduces temperatures in extensive spaces. In Vancouver, a study reported that urban forests reduced air temperatures of the surrounding areas by 5–7 °C during peak summer and outperformed smaller green spaces [10]. Green corridors that line these dense tree canopies reduced ambient temperatures by up to 3 °C across Beijing. Another example from Melbourne showed how green corridors helped ventilate spaces and created a buffer for cooling by emphasizing their effect during the summer [42]. However, despite their greater area, urban forests and corridors are good at reducing heat on a larger scale, but the implementation requires large land areas.

Whereas community gardens are smaller in scale, they are focused on localized cooling and group interaction. As in arid cities such as Phoenix, irrigated community gardens lowered localized temperatures and improved thermal comfort for surrounding neighborhoods [40]. While these gardens do not have the significant effects of urban forests or corridors, they are easier to place in dense urban areas. Overall, it can be stated that community gardens and green corridors can help mitigate citywide heat, and urban forests can provide heat mitigation on a citywide scale. Instead, combining these strategies provides a multi-scale strategy for fighting urban heat islands.

4.1.2. Evapotranspiration

Evapotranspiration, through the release of water vapor, effectively reduces urban temperatures by absorbing latent heat, making it a vital mechanism for mitigating the urban heat island (UHI) effect.

Green Roofs vs. Urban Parks

The local cooling benefits of green roofs are through evapotranspiration and insulation of the rooftop. Even in dense urban areas, irrigated green roofs have the cooling potential to reduce rooftop temperatures by up to 4 °C, according to a study conducted in Berlin [49]. In Saint Paul, Minnesota, another study found that urban agriculture placed on green roofs increased evapotranspiration rates and lowered rooftop and adjacent air temperatures by 2–4 °C during the summer [55]. In Tokyo, as in other cities, the cooling effects of irrigated green roofs on reducing energy demand manifested, and green roofs could also function as cooling and energy-saving interventions [30]. On a larger scale, urban parks can better achieve cooling. For example, inhibiting evaporative cooling from park trees in Taipei City reduced park air temperature by up to 3 °C during the day [56]. In Xuzhou, China, another analysis found that increasing the evapotranspiration within parks mitigated the UHI effects associated with reducing temperatures in surrounding neighborhoods [40]. Thus, it can be stated that green roofs are practical for high-density zones, whereas urban parks are indispensable for regional climate regulation through city-wide cooling by evapotranspiration.

Community Gardens vs. Street Trees

Evapotranspiration is used to obtain localized cooling in community gardens. In Saint Paul, Minnesota, experiments found that gardens reduced air temperatures surrounding the gardens by up to 3 °C, since turfgrass plots were found to be less effective because of higher evapotranspiration rates [55]. Community gardens in warm temperate climates, such as Algeria, further buffered community microclimates by mitigating heat through evaporatively shaded (hot spot) conditions and high evapotranspiration rates [57].

Instead, street trees offer moderate evapotranspiration. A review of various urban sites demonstrated that tree-lined streets in areas like Manchester could lower air temperatures by 1–2 °C during peak heat hours [48]. In Biskra, Algeria, street trees cooled pedestrians through evapotranspiration and shading, and similarly contributed to reducing heat through mitigation [57]. Linear cooling along urban corridors is critical; street trees are indispensable, while community gardens are great at reducing local temperatures. The combination of these can increase their synergistic cooling effects.

Urban Forests and Green Corridors vs. Vertical Greenery Systems

Vertical greenery systems (VGSs) are good at cooling building facades. Studies in Shenzhen, China, showed that herb and shrub hedges integrated with VGSs can reduce surface or air temperatures up to 9 °C via increased evapotranspiration. Irrigated vertical gardens in Saint Paul reduced urban air temperatures by 2 to 3 °C during warm months [55]. Similarly, the cooling potential of irrigated vertical gardens was as good or better than that of other surface types.

On the other hand, urban forests and green corridors provide large-scale temperature control. Moss et al. [58] reported air temperature reductions of 3–5 °C in green corridors in London, with evapotranspiration quantified from urban trees. Green corridors that mitigated UHI effects while enhancing natural ventilation had an even more significant openness effect [57] in Biskra, Algeria. Thus, facade cooling by vertical greenery systems makes them excellent for dense urban environments, while urban forests and green corridors offer wider, city-wide benefits. Maximizing cooling across a range of urban contexts is achievable through integrated approaches.

4.1.3. Albedo Modification

Albedo modification, which involves increasing surface reflectivity to reduce heat absorption, is an effective strategy for mitigating the urban heat island (UHI) effect, particularly in urban areas dominated by artificial surfaces.

Green Roofs vs. Urban Parks

The presence of a green roof increases rooftop cooling efficiency by reflecting solar radiation. In Baltimore and Washington, for example, field studies found that green roofs with high albedo materials cooled their roofs up to 2 °C during summer heat waves, mitigating urban heat stress in urban neighborhoods [59]. Moreover, simulations within the Yangtze River Delta, China, showed that cooling effects achieved with even 0.7 roof albedo were comparable to reducing near-surface air temperatures by 1.5 °C [60]. On the other hand, the broader urban temperature reduction through shading and albedo effects is achieved in urban parks. In Rome, Italy, it has been found that parks with reflective surfaces can decrease urban air temperatures by up to 4 °C during the daytime [61]. They bring cooling benefits to neighboring areas, benefiting cities as a whole. Thus, green roofs provide localized cooling benefits, while urban parks provide broader, city-scale cooling benefits due to their simultaneous shading and albedo effects. This response is achieved by creating complementary solutions for urban heat mitigation.

Vertical Greenery Systems vs. Street Trees

Vertical greenery systems (VGSs) increase albedo and decrease radiant heat gain to building facades. In Terni, Italy, a study reported a 3–4 °C reduction in surface temperatures when reflective green facades are used in high-density urban areas [61]. Also, reflective materials placed in vertical greenery installations in Hong Kong reduced indoor air conditioning loads by up to 15% [16]. How street trees shade and reduce direct solar radiation makes them very different from their cousins in or near the park. In Athens, Greece, it was shown that tree-lined streets reduced the surface temperature by 1–2 °C due to shading and an increase in surface albedo [62]. Vertical greenery systems are an extraordinarily effective means of cooling building facades, and street trees improve pedestrian comfort through shading. Their combined application is hypothesized to have the most significant cooling effect on urban environments.

Urban Forests and Green Corridors vs. Community Gardens

Urban forests and green corridors achieve large-scale cooling by increasing urban albedo and providing shading. Research in Sydney, Australia, demonstrated that increasing urban forest albedo reduced peak temperatures by 3 °C, significantly mitigating heat stress across the city [41]. Similarly, studies in Atlanta, Georgia, highlighted that tripling surface albedo in urban corridors decreased peak surface temperatures by 2 °C [63]. Community gardens, while smaller in scale, also provide reflective cooling benefits. A study in Singapore found that reflective materials integrated with garden layouts reduced ambient temperatures by up to 2 °C, particularly in densely populated areas [57]. Urban forests and green corridors provide extensive city-scale cooling, while community gardens are better suited for localized interventions. Combining these strategies can optimize cooling at multiple scales, improving urban resilience to heat stress.

4.1.4. Ventilation

Ventilation, driven by natural or urban design enhancements, redistributes heat and cools urban areas by improving airflow, reducing the intensity of the urban heat island (UHI) effect.

Urban Parks vs. Green Roofs

Open spaces that encourage natural airflow can create open spaces that improve ventilation in urban parks. For example, a study in Sydney, Australia, found that parks helped to produce sea breezes and lower local air temperatures by 2 °C during heat peaks in the summer [34]. Large urban parks in Harbin, China, for example, reduced UHI effects by enhancing natural ventilation and improving the thermal comfort of nearby communities [64]. Although less widespread than green walls, green roofs enhance building-level ventilation. In Tehran, Iran, green roofs lowered localized wind obstruction, enhancing rooftop cooling and lowering building temperature by 0.8 °C [65]. However, their ventilation benefits are much smaller than those in large-scale open spaces. Green roofs and urban parks do the same on the city scale while improving the local airflow in high-density urban areas. By combining these solutions, we are optimizing ventilation at multiple levels.

Urban Forests and Green Corridors vs. Street Trees

Ventilation obtains a boost from urban forests and green corridors by routing cool air in and out of urban areas. Strategically placed green corridors in Phoenix, Arizona, cooled the land surface by up to 2 °C using wind flow to distribute cooling effects regionally [37]. A study in London, UK, found that green corridors added to citywide airflow, reducing UHI effects in highly built areas by up to 50% [66]. However, the street trees are localized to help improve the pedestrian-level airflow. It has been found that tree-lined streets lead to as much as a 1.5 °C decrease in ground temperatures and improved thermal comfort from natural shading and air circulation, as in the case of Athens, Greece [62]. Both urban forests and green corridors offer large-scale ventilation benefits, while street trees offer localized cooling and pedestrian comfort. Together, these provide comprehensive UHI mitigation.

Vertical Greenery Systems vs. Community Gardens

Ventilation is partly contributed to by vertical greenery systems (VGSs), which reduce facade heat and facilitate local airflow. Other reflective green facades in Terni, Italy, cooled buildings by 3 °C; air circulation was enhanced, which reduced building surface temperatures [61]. As in Singapore, VGS installations lowered the localized UHI impacts of increased air mixing and decreased radiant heat exposure [29]. Community gardens promote microclimatic ventilation by introducing open green spaces in urban places. Community gardens were shown to lower air temperatures in Phoenix, Arizona, by 2 °C and to improve air circulation in adjacent communities through their open designs [35]. Therefore, dense urban environments benefit from vertical greenery systems, and community gardens improve microclimatic ventilation. Both are integrated to obtain better airflow and cooling in various urban settings.

The outstanding contributions to urban heat islands mitigation of shading, evapotranspiration, albedo modification, and ventilation in different stages of planning, design, and construction can be demonstrated by measuring the urban heat islands mitigated under fixed cooling mechanisms. The findings indicate that urban parks consistently excel at large-scale cooling through shading and evapotranspiration. At the same time, green roofs and vertical greenery systems offer localized solutions tailored to high-density areas. By combining shading and ventilation, street trees effectively improve pedestrian comfort, and urban forests and green corridors provide wide regional cooling through airflow and thermal dynamics. While small in scale, community gardens are important microclimatic providers through evapotranspiration and ventilation. Overall, these findings illustrate that a multi-tiered approach to the urban heat island challenge can build upon the myriad of strengths among each of the different green space types to meet the contrasting needs in the city.

4.2. Comparing Mechanisms for Fixed Types

Urban green spaces exhibit diverse cooling effects through varying mechanisms, including shading, evapotranspiration, albedo modification, and ventilation, which differ in their effectiveness depending on the type of green space (

Table 5. Comparison of cooling mechanisms for fixed green space types.

Green Space Type	Mechanism 1 (M1)	Mechanism 2 (M2)	Comparison Summary
Urban Parks	Shading	Evapotranspiration	Shading reduces surface temperatures by up to 5 °C [67], providing immediate localized cooling. Evapotranspiration ensures sustained air temperature reductions of 3 °C [68], even under water-limited conditions. Combined, these mechanisms work synergistically in diverse climates.
Green Roofs	Evapotranspiration	Albedo Modification	Evapotranspiration reduces rooftop temperatures by 2 °C [69], while reflective materials enhance cooling by 1 °C. Integrated designs (e.g., Berlin) improve efficiency by 25% [49], ideal for energy-demand reduction in dense areas.
Street Trees	Shading	Ventilation	Shading lowers asphalt temperatures by 22.8 °C during peak heat [70]. Ventilation amplifies cooling by 1.5 °C via airflow along corridors [71], critical for pedestrian comfort in street canyons.
Community Gardens	Evapotranspiration	Shading	Evapotranspiration reduces air temperatures by 2.5 °C in tropical climates [72], while shading lowers ground temperatures by 1 °C. Irrigated gardens achieve 3 °C cooling during peak hours [73], offering dual social and ecological benefits.
Urban Forests and Green Corridors	Shading	Ventilation	Shading reduces regional peak temperatures by 3 °C [74]. Ventilation channels cool air into cities, lowering UHI effects by 2.5 °C [75], making these systems vital for large-scale heat mitigation.

).

4.2.1. Urban Parks: Shading vs. Evapotranspiration

Urban parks employ multiple mechanisms to mitigate the urban heat island effect, making them versatile in diverse climatic and urban settings. Research in Central Europe found that tree canopies in parks reduced surface temperatures by up to 5 °C through shading. At the same time, evapotranspiration contributed additional cooling during dry periods, maintaining a consistent cooling function [67]. In another study, the combination of shading and evapotranspiration in urban parks in China helps reduce air temperatures by up to 3 °C, proving effective even under limited water supply scenarios [68]. Shading provides immediate and localized cooling, while evapotranspiration ensures sustained reductions in air temperature, highlighting the complementary effects of these mechanisms in urban parks.

4.2.2. Green Roofs: Evapotranspiration vs. Albedo Modification

Green roofs primarily utilize evapotranspiration and albedo modification to enhance urban cooling and reduce building energy demands. A study in Washington, D.C., demonstrated that irrigated green roofs reduced rooftop temperatures by 2 °C through evapotranspiration, while high-albedo materials provided an additional 1 °C reduction [69]. Another study in Berlin confirmed that integrating reflective materials with vegetation on green roofs enhanced cooling efficiency by up to 25% [49].

4.2.3. Street Trees: Shading vs. Ventilation

Street trees provide pedestrian-level thermal comfort by combining shading with natural ventilation. Research conducted in Florence, Italy, demonstrated that street trees reduced asphalt temperatures by up to 22.8 °C during peak summer through shading while facilitating airflow that lowered air temperatures by an additional 1.5 °C [70]. A similar study found that tree-lined streets amplified cooling by channeling airflow along urban corridors [71].

4.2.4. Community Gardens: Evapotranspiration vs. Shading

Community gardens combine evapotranspiration and shading mechanisms to provide localized cooling benefits while promoting social and ecological value. A study conducted in Singapore revealed that community gardens reduced air temperatures by 2.5 °C, primarily through evapotranspiration, while strategically planted trees contributed to shading, lowering ground temperatures by an additional 1 °C [72]. Similarly, irrigated community gardens reduced surrounding neighborhood temperatures by up to 3 °C, particularly during peak heat hours [73].

4.2.5. Urban Forests and Green Corridors: Shading vs. Ventilation

Urban forests and green corridors integrate multiple cooling mechanisms to provide city-wide heat mitigation and improve thermal comfort on a regional scale. A study in Sydney, Australia, showed that urban forests reduced peak summer temperatures by up to 3 °C through expansive canopy shading while facilitating natural ventilation across urban corridors [74]. In a separate study, green corridors in London enhanced airflow and reduced urban heat island effects by channeling cooler air into the city, achieving a temperature reduction of 2.5 °C [75].

4.3. Context-Specific Mechanisms

The predominant heat mitigation method depends strongly on locations and surrounding climate elements. By controlling climate variables such as humidity and solar radiation, urban planners achieve the most effective outcomes from their green space selection.

4.3.1. Geographic Conditions: Tropical Cities vs. Temperate Zones

UHI mitigation strategies in tropical cities differ significantly from those in temperate cities because of their special climatic and geographical features. Tropical cities, including Singapore and Kolkata, have high temperatures and elevated humidity levels that expand the UHI effect. The implementation of dense canopy protection methods increases the importance of shading and controlling evapotranspiration processes in tropical areas. Urban green infrastructure achieves maximum cooling effects of 6 °C in tropical megacities through diverse green patch sizes [13].

Mid-latitude cities dedicated to combating urban heat island effects predominantly adopt albedo-enhanced techniques like reflective roofs and reflective surface pavements. Seasonal shading strategies typically rely on deciduous trees as part of vegetation-based cooling efforts in sound urban management. Studies between tropical and temperate zones indicated that tropical cities show minimal reaction to albedo-based strategies [76].

4.3.2. Climatic Conditions: Arid Areas Versus Humid Zones

Arid regions have specific UHIs, with water scarcity limiting vegetative mitigation. In this respect, cities like Marrakesh and Phoenix can only have bare soil and built-up areas that significantly affect the land surface temperature. Approaches in these regions often include using arid-resistant vegetation and introducing reflective materials to reduce heat gain. For instance, high-albedo pavements coupled with low-water-use landscaping have effectively brought down daytime temperatures in arid climates [77].

In the urban areas of subtropical cities like Wuhan, the humid climate makes the contribution of vegetation very important for mitigating UHI effects. In general, vegetation cooling is enhanced by higher levels of humidity, which raises the evapotranspiration rates. Comparing semi-humid Xi’an and humid Wuhan, it was felt that vegetation-based strategies act more effectively in semi-humid climates. However, in humid regions, optimal results are obtained with vegetation-water combination strategies [78].

Shading takes precedence in arid cities such as Phoenix, where tree canopies and reflective surfaces effectively counter intense solar radiation and lower surface temperatures [36]. Furthermore, appropriately positioned street trees in regions of high solar radiation can provide vital shading to roadways and pedestrian zones, reducing surface temperatures and improving thermal comfort. Delhi’s urban planning approach emphasizes large-scale greenery to counteract intense solar radiation and enhance evapotranspiration, making it a model for UHI mitigation in semi-arid climates.

4.4. Practical Implications

To achieve UHI mitigation with more appropriate means for strategic deployment of the required infrastructure, comparative analyses examine a range of mechanisms concerning greening space types, whose contributions are valid in various urban morphological setting conditions. By leveraging the unique strengths of shading, evapotranspiration, and albedo modification, urban planners can create tailored solutions for diverse urban contexts.

4.4.1. Multi-Functional Green Space Design

Green spaces should incorporate different cooling mechanisms to perform all the functions effectively. Urban parks with dense tree canopies should be focused more on suburban and low-density urban areas where the land allows. Their shading and ventilation effects can reduce ambient temperatures as high as 3 °C, benefiting surrounding neighborhoods with broad-scale cooling [47]. New York’s large-scale afforestation efforts, like MillionTreesNYC, underline the importance of urban forestry in reducing surface heat and providing thermal comfort across densely populated regions. On the other hand, the vertical greenery system and the roofs represent green systems that give life to highly cooled hubs because there is no room for horizontal space. Green roofs decrease the temperature on rooftops up to a difference of 2 °C, while greenery supports better shading, adding quality to the flow of air along tight urban corridors [32,40].

4.4.2. Recommendation of Policies and Urban Planning

Several strategies will help mitigate UHIs equitably and effectively. Firstly, urban zoning regulations must make green roofs and vertical greenery in new developments a requirement for any realistic possibility of meeting the cooling demands of dense urban cores. Delhi’s integration of green corridors into residential and industrial zones offers a replicable model for expanding greenery in rapidly urbanizing areas with limited vegetation. Moreover, targeted investment in marginalized neighborhoods to break the cycle of social inequities impeding poor and/or vulnerable people from reaping the benefits of greeneries could mitigate UHI. Lastly, high-resolution thermometry and LiDAR have provided planners with insight into making priority investments in and planning green spaces within existing green infrastructure.

5. Challenges and Limitations in Applying Urban Green Space for UHI Mitigation

5.1. Spatial Constraints

A crucial challenge in applying urban green space to mitigate the UHI effect is its application to high-density built-up areas (

Table 6. Challenges in urban green space Implementation.

Challenge	Example 1	Proposed Solution 1	Technological Support 1	Example 2	Proposed Solution 2	Technological Support 2	Reference
Spatial Constraints	Dense urban cores	Vertical greenery, rooftop gardens	LiDAR for optimizing space allocation	Limited open spaces	Multi-functional green walls	3D modeling for compact urban layouts	[43]
High Maintenance Costs	Green roofs	Efficient irrigation systems	Remote monitoring systems	Vertical greenery	Public-private partnerships	AI-based maintenance scheduling	[79]
Data Inaccuracy	Remote sensing limitations	Ground-truthing	High-resolution satellite imagery, AI models	Inconsistent field data	Integrated monitoring systems	Drone-based thermal mapping	[45]
Uneven Distribution	Marginalized neighborhoods	Equitable green space policies	GIS mapping for vulnerability identification	Socioeconomic disparities	Targeted green infrastructure	Community-driven participatory	[80]

). Mostly, spatial constraints in the urban context have eliminated the feasibility of incorporating any large-scale green spaces, such as parks or even urban forests. This is an acute issue in urbanized cities, given that most land is apportioned for infrastructure and housing buildings. While vertical greenery or green roofs are effective to a great extent, the different architectural limitations and their demanding maintenance reduce their large-scale applicability in urban planning [43]. Spatial constraints indeed provide the need for innovative approaches incorporating green spaces into existing urban design, such as compact rooftop gardens and multi-functional green walls. Overall, in densely built urban cores, the lack of open spaces limits the feasibility of large-scale green infrastructure like parks or urban forests. Vertical greenery systems and rooftop gardens offer compact alternatives. Technologies such as LiDAR and 3D modeling facilitate efficient space utilization, ensuring greenery is optimally integrated even in constrained environments.

5.2. High Maintenance Costs

Another problem lies in the limitation posed by resolution in most remotely sensed technologies, widely used to measure land surface temperature and vegetation cover for detection. Additionally, satellite-derived data may also be interfered with by the atmosphere, which can further compromise accuracy and give rise to disparities in thermal readings [79]. To properly understand the benefits of space greening for urban heat island reduction, passive remote sensing requires verified assessment approaches. An improved tracking system needs to combine data from satellites and direct local observations. Costs associated with these measures become manageable through both efficient irrigation programs and public-private collaborative initiatives. AI-based maintenance scheduling and remote monitoring enhance efficiency by observing processes to inform maintenance and component replacement decisions.

5.3. Data Inaccuracy

Due to the uneven distribution of green spaces throughout urban areas, residents face increased environmental and social inequalities. Marginal neighborhoods often lack natural green areas on their territory, resulting in heightened exposure to extreme weather and heat stress effects. Equitable urban planning policies that focus on proper green space distribution in underserved neighborhoods represent a critical priority, according to Pussella and Li [45]. Without targeted interventions, the benefits of UHI mitigation by urban green spaces may continue to elude those who need them more. Therefore, Ground-truthing and integrated monitoring systems combining satellite imagery, AI models, and drone-based thermal mapping improve data accuracy, enabling precise assessment and planning.

5.4. Uneven Distribution

Green areas within urban spaces have remained vital in taming the UHI effect. By ensuring mitigation against these challenges of spatial constraints, data accuracy, and fair distribution, cities can then realize the full potential of GI regarding increasing resilience and improving thermal comfort within urban spaces. Equitable green space policies and targeted green infrastructure interventions can address these disparities. GIS and community-driven participatory mapping help identify priority areas for green space development, ensuring resources are allocated where needed most [80].

6. Future Directions and Policy Implications

6.1. Policy Recommendations

The future of urban green space as a strategy for mitigating the urban heat island (UHI) effect depends on the adoption of robust, targeted policy frameworks that move beyond general incentives. Policymakers and urban planners should implement enforceable measures such as mandating a minimum percentage of green space—typically 20–30%—in all new residential and commercial developments, following the example set by Singapore’s Green Plan 2030 [81]. Tiered incentives, including tax credits, expedited permitting, or density bonuses, should be offered to developers who install high-performance green roofs and vertical gardens that meet specific standards for cooling and biodiversity [36]. In addition, targeted grant programs can be established to support the retrofitting of existing buildings with green infrastructure, especially in neighborhoods that experience high UHI intensity and house vulnerable populations [6].

Urban tree canopy ordinances should also be enacted, setting clear targets for tree coverage and providing dedicated funding for both planting and maintenance, as demonstrated by Melbourne’s Urban Forest Strategy [82]. To ensure that these policies are equitable and publicly supported, participatory planning processes should be employed, engaging communities in the design and siting of new green spaces and using participatory mapping to identify priority areas [45]. Furthermore, UHI mitigation targets and green infrastructure requirements should be integrated into municipal climate action plans and aligned with the United Nations Sustainable Development Goals [83]. For instance, Los Angeles has successfully implemented rebates for cool roofs and urban tree planting, achieving temperature reductions of 2–3 °C in targeted neighborhoods [84].

6.2. Technological Innovations

Recent technological advancements are transforming the monitoring, planning, and management of urban green spaces for UHI mitigation. Municipalities are now using high-resolution LiDAR mapping to generate detailed three-dimensional models of urban tree canopies, which enables precise quantification of shading, evapotranspiration potential, and the identification of gaps in green coverage [85]. The fusion of LiDAR with hyperspectral and thermal imagery further enhances the ability to assess vegetation health, surface temperatures, and the spatial distribution of cooling benefits at the neighborhood scale [11].

Automated drone surveys equipped with LiDAR and multispectral sensors are increasingly being deployed to rapidly survey large urban areas, providing real-time data that urban planners can use to identify UHI hotspots and prioritize interventions [86]. In addition to these remote sensing technologies, cities are adopting GIS-based decision-support tools that combine environmental, demographic, and climate data to simulate the cooling effects of different green infrastructure scenarios and optimize their placement for maximum impact [36]. For example, New York City has utilized LiDAR and thermal imaging to map tree canopy cover and surface temperatures, guiding targeted tree planting and green roof installation in the most heat-vulnerable neighborhoods [85].

6.3. Recommendations for Future Research

Future research should prioritize long-term, interdisciplinary studies that evaluate the effectiveness of green infrastructure for UHI mitigation across a range of climates and urban forms. Multi-year impact assessments are needed to track the thermal, ecological, and social benefits of green infrastructure projects, providing critical data for adaptive management and policy refinement [71]. There is also a need to develop robust methodologies for quantifying the co-benefits of urban green spaces, such as carbon sequestration, biodiversity enhancement, and improvements in public health, alongside their direct impact on UHI mitigation [59].

Ensuring the equitable distribution of green infrastructure is another key research priority, with a focus on strategies that prioritize heat-vulnerable and underserved communities [45]. Finally, the integration of artificial intelligence and machine learning with remote sensing data holds promise for automating the identification of optimal sites for green infrastructure and predicting future UHI trends, enabling cities to proactively design and manage climate-resilient urban landscapes [11]. Through innovative policies, advanced monitoring tools, and interdisciplinary research, cities can make significant progress toward sustainable and climate-resilient urban environments.

7. Conclusions

The role of urban green spaces is beyond doubt in mitigating the UHI effect, whose cooling effects have been demonstrated by providing shade, evapotranspiration, and modification in albedo. This review brings forth the idea that green infrastructure, backed by remote sensing and GIS technologies, may enhance thermal comfort and considerably reduce heat stress within the urban atmosphere. For instance, the use of remote sensing gives essential results related to urban heat and vegetation patterns. The analysis performed by GIS points out the best locations for green spaces. As a result, conservation initiatives are based on data and installed where they will be most useful. With this approach, people feel more comfortable, and urban heat stress is lowered.

Thus, this would develop an important method for reducing urban heat problems, with parks, green roofs, and street trees being the elements that will make this strategy broadly viable to overcome the many challenges related to climate change. The implications are deep in policy and urban planning, meaning the city governments need to recognize green spaces as part of an environmental, social equity, and public health asset. By prioritizing integration in urban design, policymakers have the opportunity to enhance climate resilience and address the needs of vulnerable populations. It requires a commitment to policies that equitably distribute green space and new technologies in monitoring and optimization of their impacts. Future research must be done to develop evidence based on green infrastructure in various climatic and urban contexts. Interdisciplinary research, combining environmental science, urban planning, and social equity considerations, stands a better chance of providing holistic solutions to mitigate UHI. In this respect, interaction by researchers and practitioners across such domains will help unlock the full potential of urban green spaces as a cornerstone in sustainable urban development.