Exploring the Heat Mitigation Effects of Urban Climate Adaptation Facilities

Abstract

Urban heat islands (UHI), which are exacerbated by climate change, significantly increase heat stress, particularly affecting vulnerable populations, such as the elderly and children. This study evaluates the effectiveness of various urban heat mitigation technologies, including cooling fog systems, cool roofs (reflective paint), shading structures, and small water paths, in reducing temperatures and enhancing thermal comfort. Field tests were conducted from 2021 to 2023 across Gimhae-si, Yechun-gun, Geyang-gu, and Sangju-si, with support from the Korean Ministry of Environment. The results demonstrated that cooling fog systems provided immediate temperature reductions, lowering ambient temperatures by up to 3.1 °C, while cool roofs reduced surface temperatures by 2–3 °C. Shading structures reduced surface temperatures by up to 10 °C, and small water paths cooled air temperatures by up to 1.5 °C, also increasing humidity and improving thermal comfort. The findings suggest that a combination of these technologies can effectively mitigate urban heat stress, especially in areas with vulnerable populations.

1. Introduction

1.1. Background and Problem Statement

The urban heat island (UHI) effect and climate change pose significant challenges to modern cities worldwide, leading to increased thermal stress, particularly during heat waves, and creating a pressing need for innovative cooling solutions in urban environments [1,2]. The UHI effect results from the replacement of natural landscapes with heat-absorbing materials, such as buildings, roads, and other urban infrastructure [2,3]. These surfaces absorb and re-emit solar radiation, causing urban areas to be significantly warmer than their rural surroundings, particularly during the summer months [4]. This temperature differential not only raises energy consumption but also heightens health risks, especially for vulnerable urban populations, such as the elderly and those with preexisting health conditions [5,6,7].

The combined impact of the UHI effect and climate change is most pronounced during heatwaves, which have become more frequent and severe owing to rising global temperatures [8]. Vulnerable populations, including the elderly, children, and individuals with health issues, face elevated risks under these conditions [9,10]. This underscores a critical need for effective heat mitigation strategies to protect public health in urban environments [11,12]. Although various studies have explored UHI and climate change individually, there is limited research on the combined effects of multiple heat mitigation technologies in real-world urban settings this research gap; this study provides an in-depth evaluation of the combined effectiveness of various heat mitigation technologies. In response to the challenges posed by UHI and climate change, the Korean Ministry of Environment initiated a comprehensive project between 2021 and 2023 to test and implement various urban heat mitigation strategies [13,14]. Field tests were conducted in Yechun-gun, Sangju-si, Geyang-gu, and Gimhae-si, where technologies such as cooling fog systems, cool roofs, shading structures, and small water paths were deployed to reduce urban temperatures and enhance thermal comfort.

For this study, IoT-based environmental sensors were installed to monitor temperature, humidity, wind speed, and solar radiation in real time. Data were uploaded automatically every five minutes using devices such as the Ecowitt GW1101 Wi-Fi Weather Station with WS69 (Ecowitt, Shenzhen, China) and T&D TR-71wf (T&D Corp., Matsumoto, Japan) Data Logger temperature sensors, which were calibrated before installation (Table 1). These devices are capable of capturing the necessary environmental changes in temperature, humidity, wind speed, and solar radiation that are essential for evaluating urban cooling technologies. By providing high-resolution data, these sensors capture the nuances of each technology’s impact. This study, therefore, offers a unique perspective by integrating multiple data streams to assess the efficacy of combined urban cooling technologies under real-world conditions and contributing valuable insights for urban planners and policymakers.

1.2. Urban Heat Mitigation Technologies

Several technologies have been developed to address the UHI effect and enhance thermal comfort in urban areas [15,16,17]. These include both active and passive cooling solutions that target different aspects of urban heat stress [18,19]. Each technology offers unique benefits and potential limitations, which this study explores to provide a comprehensive analysis of their effectiveness.

• Cooling Fog Systems: These systems use evaporative cooling to lower ambient temperatures in outdoor spaces by dispersing fine water droplets into the air, which cools the surrounding environment as they evaporate [20,21]. Cooling fog systems provide immediate temperature reductions, making them highly effective in high-traffic public areas, although water usage and maintenance requirements should be considered.

• Cool Roofs (Reflective Paint): Reflective coatings minimize heat absorption in buildings, thereby reducing surface and indoor temperatures [22,23]. Cool roofs offer passive, energy-efficient cooling, which is particularly beneficial for reducing the energy demands of air conditioning, although long-term maintenance and reapplication may be necessary.

• Shading Structures: Shading structures block direct sunlight, thereby reducing surface temperatures and improving thermal comfort in public areas, such as parks, playgrounds, and transit stops [24,25,26]. These structures provide effective shade and reduce solar exposure, offering low-maintenance cooling for outdoor spaces. However, they may not lower ambient temperatures significantly outside the shaded zones.

• Small Water Paths: These passive cooling solutions use water channels in urban parks and public spaces to cool surrounding air through evaporative effects. Small water paths provide steady cooling and increased humidity in nearby areas, contributing to thermal comfort, especially during peak heat hours, although regular upkeep is needed to prevent water loss and ensure operational efficiency.

While these technologies show promise individually, there is limited research on their combined effects in real-world urban environments. Furthermore, previous studies have rarely evaluated these technologies’ economic, maintenance, and social acceptance aspects, which are essential for selecting optimal solutions for urban heat mitigation. This study addresses this gap by evaluating the synergistic effectiveness of these technologies in various settings.

1.3. Research Objectives

The primary aim of this study is to assess the effectiveness of four urban heat mitigation technologies—cooling fog systems, cool roofs, shading structures, and small water paths—in reducing temperatures and improving thermal comfort, with a particular focus on vulnerable populations. Specifically, this study seeks to achieve the following:

1. Evaluate the temperature reduction capabilities and maintenance requirements of each technology in urban settings.

2. Compare the effectiveness of active cooling technologies (cooling fog) with that of passive solutions (cool roofs, shading structures, and small water paths).

3. Analyze social acceptance and economic feasibility factors associated with each technology to provide a practical framework for urban planners.

4. Provide actionable insights for urban planners and policymakers on the deployment of these technologies to protect vulnerable populations from extreme heat.

1.4. Significance of This Study

This study provides valuable empirical data from real-world experiments, offering insights into the performance of heat mitigation technologies under urban conditions. It contributes to the understanding of how combined urban heat mitigation strategies can be optimized for both cooling efficiency and cost-effectiveness. Its significance lies in several areas, as follows:

• Its significance lies in several areas. It emphasizes the protection of vulnerable populations, such as the elderly, children, and low-income communities, who are most at risk during extreme heat events.

• The findings can inform urban planning and policy initiatives aimed at reducing heat stress, ensuring that at-risk populations are protected from the impacts of climate change.

• By evaluating the sustainability, cost, and social acceptance of these technologies, this study provides a balanced perspective on the practical implementation of heat mitigation strategies.

• By sharing the results of these experiments, this study provides a blueprint for other cities looking to implement heat mitigation strategies cost-effectively.

The results can serve as a reference for global urban planners and policymakers, aiding in the adaptation of heat mitigation solutions to specific urban contexts while considering maintenance needs and public acceptance.

2. Principles and Review of Urban Heat Mitigation Technologies

2.1. Principles and Effects of Urban Heat Mitigation Technologies

In response to UHI and climate change, various heat mitigation technologies have been developed and implemented. The primary technologies examined in this study include the following:

• Cooling Fog Systems: This technology disperses fine water droplets into the air, which cools the surrounding environment as they evaporate. Cooling fog is particularly effective in public spaces, offering immediate temperature reduction in high-traffic outdoor areas. However, water consumption and maintenance requirements present limitations that must be addressed to ensure sustainable usage.

• Shading Structures: Shading structures block direct sunlight and reduce the temperature in the shaded areas. These structures are commonly installed in parks, playgrounds, bus stops, and other public spaces to reduce heat stress. Studies have shown that shading can significantly lower the ambient air temperature and perceived discomfort. Material selection and design are essential for maximizing shading effectiveness while minimizing maintenance requirements.

• Cool Roofs (Reflective Paint): Reflective coatings applied to building exteriors reflect solar radiation, reducing surface and indoor temperatures. This technology is especially effective in lowering the energy demand for cooling during summer and mitigating UHI effects. Cool roofs offer a passive, energy-saving approach, but long-term durability and the frequency of reapplication need consideration.

• Small water paths: These small artificial water channels help to absorb and dissipate heat from the surrounding environment. They provide cooling in urban parks and public spaces and offer psychological benefits by creating tranquil, pleasant environments for rest and relaxation. Regular upkeep is required to prevent water loss and maintain cooling effectiveness, making maintenance a key factor in their application.

The extensive field tests conducted with the support of the Korean Ministry of Environment in cities such as Yechun-gun, Sangju-si, Geyang-gu, and Gimhae-si offer valuable insights into the practical implementation of these technologies in real-world settings. This study provides empirical data that compare these technologies not only in terms of cooling efficiency but also with respect to economic, social, and environmental factors.

2.2. Review of Previous Studies

Although extensive research has been conducted on individual heat mitigation technologies, limitations remain in the literature [18]. For instance, studies on cooling fog systems demonstrate effective temperature reduction but often neglect the sustainability challenges posed by high water usage and maintenance demands [21]. Research on cool roofs highlights surface temperature reductions [23], yet few studies address their long-term durability and potential need for reapplication. While shading structures are widely recognized for blocking solar radiation [24], there are limited data on their impact on ambient temperatures beyond shaded zones. Additionally, small water paths are known for their evaporative cooling effects, but water loss and operational challenges in dry climates are rarely explored.

The current literature also lacks studies on the combined application of these technologies in urban environments. Moreover, few studies consider economic feasibility, maintenance requirements, and social acceptance—factors that are critical for sustainable urban planning [11]. This study aims to fill these gaps by evaluating the synergistic effects of multiple technologies, assessing practical challenges, and offering a comprehensive framework for urban heat mitigation that incorporates community acceptance and cost considerations. Several studies have evaluated individual heat mitigation technologies, but few have explored the combined effects of multiple technologies in urban environments. This study addresses this gap by examining the synergistic effects of cooling fog, shading structures, cool roofs, and waterway shelters in mitigating urban heat stress. Additionally, this review highlights gaps in the literature, particularly regarding the economic feasibility and long-term sustainability of these technologies.

• Shading Structures: Shading structures are well-known for their ability to reduce solar exposure, but there is relatively little research quantifying their specific temperature reduction effects. Studies suggest that the material and design of the shading structure significantly impact its effectiveness. For instance, natural tree shade can reduce surrounding air temperatures by up to 5 °C, while artificial shading structures demonstrate similar temperature reductions [27,28].

• Cool Roofs: Cool roofs have been extensively studied and are shown to reduce surface temperatures by up to 15 °C by reflecting solar radiation, which significantly lowers the amount of heat absorbed by the building. This reduction in surface temperature leads to a decrease in energy demand for cooling, particularly during summer months [26,29]. However, factors like maintenance costs and durability remain underexplored, indicating a need for further research.

• Cooling Fog: Cooling fog systems are effective in lowering ambient temperatures, particularly during heatwaves, with reductions of 4 °C to 6 °C reported in various studies. However, there are concerns regarding water consumption, prompting further research into optimizing these systems to balance cooling efficiency with resource conservation [30,31].

• Waterway Shelters: Water features, such as small water paths, consistently reduce both surface and air temperatures by 2 °C to 4 °C through evaporative cooling. These features are particularly effective in parks and outdoor spaces, providing not only passive cooling but also aesthetic and psychological benefits. However, challenges such as maintenance and ensuring that the system operates effectively under all conditions have been noted [32,33].

The studies reviewed underscore the positive impacts of various heat mitigation strategies in urban environments. Notably, cool roofs and cooling fog systems show immediate and effective temperature reductions, while shading structures and water features provide long-term, passive cooling. However, limited research exists on the combined economic, environmental, and social impacts of these technologies, which is a gap this study aims to fill. This study will build on these findings by evaluating the combined effect of these technologies in mitigating heat stress in urban environments.

2.3. Significance and Application of Combined Technologies

This study provides a comprehensive evaluation of urban heat mitigation technologies, focusing on their real-world applicability and potential to reduce heat stress in urban environments. The key contributions of this study are as follows.

• Integrated Approach: Unlike previous research that focused on individual technologies, this study evaluated multiple technologies in combination, providing a holistic analysis of their collective impact on urban heat mitigation.

• Field-tested Validation: The field tests conducted in collaboration with the Korean Ministry of Environment over multiple years (2021–2023) offer valuable practical data. These data demonstrate how these technologies perform in real-world urban settings, offering insights that can inform future urban planning and policy efforts. This study also addresses practical challenges, such as maintenance and costs, thereby enhancing its relevance for policymakers and planners.

• Policy Implications: The findings from this study provide actionable insights for local governments in Korea and globally, particularly those aiming to implement heat mitigation strategies to protect vulnerable populations. This study sets a benchmark for other local governments and provides a reference for large-scale heat mitigation initiatives that require significant investment, energy, and time. By incorporating a broader analysis of costs, maintenance, and community acceptance, this study delivers a well-rounded perspective for practical urban policy applications.

3. Methodology

3.1. Overview of Technologies Evaluated

This study evaluated the cooling effects of several urban heat mitigation technologies, including cooling fog, cool roofs (reflective paint), shading structures, and small water paths, focusing on their effectiveness in improving thermal comfort for vulnerable populations exposed to extreme heat. These field tests were conducted with support from the Korean Ministry of Environment between 2021 and 2023 as part of a national initiative to mitigate climate-induced heat stress in urban communities.

Study Location Selection and Criteria

Locations were carefully chosen based on a set of criteria to ensure diverse testing environments and represent different urban characteristics, as follows:

• Climate Variability: The selected locations—Yechun-gun, Sangju-si, Geyang-gu, and Gimhae-si—represent a range of climatic conditions in South Korea, from humid continental to subtropical, to evaluate each cooling technology’s adaptability to different climates.

• Urban Density and Vulnerable Populations: These areas have varying levels of urban density, including both high-density city centers and suburban regions, where vulnerable populations, such as elderly residents, children, and individuals with preexisting health conditions, are more likely to experience adverse health impacts from extreme heat.

• Documented Urban Heat Issues: Each site has specific characteristics that contribute to urban heat island (UHI) effects, including dense infrastructure, limited green space, or reliance on concrete surfaces, making them ideal for studying cooling interventions.

• Public Space Usage: Selected sites are located in or near high-traffic public spaces like playgrounds and community parks, where cooling measures can directly benefit daily users and provide insights into effective design for community areas.

This study was conducted in four urban areas across South Korea: Yechun-gun, Sangju-si, Geyang-gu, and Gimhae-si. Each location was selected based on unique urban and environmental characteristics, as well as the presence of vulnerable populations. These sites provided a range of conditions to test the effectiveness of heat mitigation technologies.

• Gimhae-si, Jinyeong-eup

  This urban area is located in southeastern South Korea near industrial centers and experiences high summer temperatures. Reflective coatings (cool roofs and walls) were applied to buildings to examine their impact on surface and ambient temperatures.

• Yechun-gun

  This is a predominantly rural area in Gyeongsangbuk-do province with a significant aging population. The cooling fog system was installed in a public playground to assess its effectiveness in rural community spaces.

• Geyang-gu, Incheon

  This is a dense, urbanized district with high UHI effects due to concrete infrastructure. Shading structures were installed to evaluate their potential to lower surface temperatures and improve thermal comfort in heavily populated zones.

• Sangju-si

  This is a central urban area with a humid continental climate, where Namsan Park was chosen to test small water paths’ cooling benefits for elderly residents and others who frequent green spaces.

3.2. Experimental Setup

3.2.1. Cool Roof (Reflective Paint) Experimentation

• Objective: To evaluate the cooling performance of reflective coatings (cool roofs) applied to building surfaces and assess their impact on the surface and ambient temperatures.

• Study Location: Reflective paint was applied to the rooftops and external walls of buildings in Jinyeong-eup, Gimhae-si, located in southeastern South Korea near industrial centers, such as Busan and Changwon. This region, which has a humid subtropical climate (Cfa), with hot, humid summers, faces significant heat stress during summer due to its inland location and urban development, exacerbating the urban heat island effect. These conditions make Jinyeong-eup an optimal test location, providing relevant insights into the applicability of cool roof technology for cities facing similar climate challenges globally [34,35].

• Experimental Design:

  • Three test sites were selected for comparison refer to Figure 1 and Table 2

    • H1: Cool roof and cool wall applied.

    • H2: Cool wall only.

    • H3: Control site (non-applied).

  • Monitoring Equipment: IoT-based temperature and humidity sensors were installed to continuously monitor changes in the temperature and humidity levels before and after the application of reflective coatings. In addition to real-time temperature readings, the sensors measured variations across multiple heights, enabling a more comprehensive understanding of cooling effects at different levels (Table 3).

  • Data Collected:

    • Surface and Indoor Temperatures: Surface temperatures of rooftops and walls, indoor temperatures, and ambient air temperatures above 1.5 M from the surface were measured using T&D TR-71wf data logger (T&D Corp., Matsumoto, Japan) temperature sensors from 27 August to 1 September 2021. These data provided insights into both the direct cooling effects on surfaces and the indirect impacts on indoor temperatures, addressing both building cooling and external comfort.

    • Temperature Gap Analysis: To further demonstrate the cool roof’s advantages, a temperature gap analysis was conducted between rooftop and indoor temperatures, highlighting the potential of cool roofs to reduce heat transfer into buildings.

    • Comparative Analysis of Efficiency: In addition to temperature reduction, data on energy usage reductions, maintenance, and operational costs were evaluated, enabling a more holistic comparison across different applications and offering valuable data for urban policymakers.

3.2.2. Cooling Fog Experimentation in Yechun-gun

• Objective: To assess the cooling effects of a cooling fog system installed in a public outdoor space specifically designed to improve thermal comfort for vulnerable populations and high-traffic areas, such as playgrounds. This experiment also evaluates the system’s effectiveness in reducing perceived discomfort due to heat and its potential impact on energy demands for surrounding buildings.

• Study Location: A cooling fog system was deployed at a children’s playground in Yechun-gun, Gyeongsangbuk-do, located in northern South Korea (Figure 2). This temperate region (Dwa climate) experiences hot, humid summers and cold winters. Climate change has increased the frequency of heatwaves, making Yechun-gun—primarily rural and with a significant aging population—more vulnerable to heat-related risks, particularly during peak summer months. These conditions make Yechun-gun a strategic location for deploying cooling fog systems, which can reduce temperature stress in open public areas and provide immediate cooling relief in high-traffic zones. The implementation of cooling fog systems is particularly crucial in regions like Yechun-gun, where local populations are heavily reliant on outdoor public spaces for daily activities, and where public health infrastructures may not be as readily equipped to handle the intensifying climate conditions [35,36,37].

• Experimental Design:

  • Fog System Setup: Fog nozzles were installed at heights between 3 and 4 m, and the system was operated during the hottest hours of the day (12:00–16:00). A nearby control area without cooling fog was used for comparison.

  • Monitoring Equipment: IoT temperature sensors were placed at different distances from the fog system and sunny zone 9 m to measure the cooling effect. Multiple sensors were used to assess temperature variations across various distances, capturing both immediate and residual cooling effects (Figure 3, Table 4).

    • Ecowitt WS69 (Ecowitt, Shenzhen, China) IoT-based temperature sensors were installed around the cooling fog zone (W1) and a sunny control zone (W2).

  • Data Collected:

    • Ambient air temperature (measured before and after fogging)

    • Humidity levels around the system

    • Measurement Period: The IoT sensors monitored temperature and humidity levels from 13 September 2021, focusing on peak afternoon hours.

3.2.3. Shading Structure Experimentation in Geyang-gu

• Objective: To evaluate the impact of shading structures on reducing heat exposure in public outdoor areas, particularly for vulnerable populations, such as children and the elderly. This study also aims to examine the effect of shading on perceived thermal comfort and its potential to reduce energy demands for nearby buildings by lowering ambient temperatures.

• Study Location: Shading structures were installed in key public spaces within Geyang-gu, which is a district in Incheon Metropolitan City, South Korea. Located near the Yellow Sea, Incheon has a coastal climate with warm, humid summers and cold winters. Geyang-gu, a rapidly urbanizing area, experiences the urban heat island (UHI) effect, which intensifies local temperatures. The district’s dense population and extensive concrete surfaces contribute to elevated heat, affecting vulnerable groups. Shading structures in areas like playgrounds and rest spots provide passive cooling by blocking solar radiation, helping to reduce heat stress and improve comfort for public space users in Geyang-gu (Figure 4). To address these challenges, shading structures have been installed in public spaces, such as playgrounds and rest areas, where they provide passive cooling by blocking direct solar radiation. These structures aim to create cooler, more comfortable outdoor environments, contributing to public health and reducing energy dependence for cooling. These structures provide passive cooling by blocking direct solar radiation, reducing heat stress for vulnerable populations, and creating cooler, more comfortable outdoor environments [38,39,40].

• Experimental Design:

  • Shading Setup: Large shading structures were installed in playgrounds and outdoor rest areas to block direct sunlight and provide thermal comfort to pedestrians and children. The shading structures were designed with materials that maximized solar reflectivity and reduced heat absorption.

    • S1: Cool shadow zone.

    • S2: Sunny zone.

  • Monitoring Equipment: T&D TR-71wf data logger (T&D Corp., Matsumoto, Japan) temperature sensors were placed under the shading structures to measure the reduction in ambient temperatures, while control areas without shading were monitored for comparison. The sensors were positioned at pedestrian height to capture temperature variations that impact individuals directly (Figure 5, Table 5).

  • Data Collected:

    • Surface temperature beneath the shading structures and sunny zone.

    • Measurement Period: Data logger sensors were installed under the shading structures in a playground. Comparisons were made with nearby unshaded areas from 30 September to 4 October 2021. Sensing data were measured every 5 min.

3.2.4. Small Water Path Experimentation in Sangju-si

• Objective: To assess the cooling effects of waterway shelters designed for passive cooling in public parks, particularly for vulnerable populations, such as the elderly and young children. This study also evaluates the water path’s influence on local microclimates and its potential to create thermally comfortable environments in green urban spaces.

• Study Location: A small water path was installed in Namsan Park, Sangju-si, Gyeongsangbuk-do, central South Korea. This inland region experiences a humid continental climate with hot summers and cold winters, making it vulnerable to extreme heat and frequent summer heatwaves. The 150 m-long water path provides passive cooling through evaporative effects, creating a cooler microclimate that benefits park visitors. This feature also enhances the park’s aesthetic and psychological appeal, providing a comfortable environment amid rising temperatures due to climate change (Figure 6). The deployment of passive cooling systems, such as small water paths, in regions like Sangju-si is crucial to adapting to the changing climate by helping to alleviate heat stress in outdoor public spaces [40,41,42].

• Experimental Design:

  • Small water path installation: Shallow water channels were constructed along the park walkways, offering cooling effects through evaporative cooling. Control areas without water features were included for comparison (Figure 7, Table 6).

    • P1: Small water path.

    • P2: Sunny zone.

  • Monitoring Equipment: Ecowitt ws69 (Ecowitt, Shenzhen, China) temperature and humidity sensors were positioned in the center of the paths and sunny zone, which was 6 m away from the path, monitoring temperature differences between areas cooled by water and sunny zone areas without water features to compare cooling effects.

  • Data Collected:

    • Surface temperature of the walkways near the water channels.

    • Air temperature at pedestrian level.

    • Relative humidity levels and solar radiation data.

  • Measurement Period: Wet-bulb temperature and humidity sensors were positioned along the water path (P1) and in a sunny control zone (P2). Data were collected from 5–8 August 2023, with a focus on midday temperature and humidity trends. Data were uploaded to a server every 5 min, allowing for the real-time monitoring of temperature fluctuations and humidity levels.

3.3. Data Analysis

The data collected from each experimental site were analyzed to evaluate the effectiveness of each cooling technology in reducing heat stress and improving thermal comfort. The following analysis methods were applied:

3.3.1. Temperature Reduction Comparison

• Surface and Ambient Temperature: The primary method of analysis was the comparison of surface and ambient air temperatures before and after the installation of each technology. For each experimental site, temperature data were gathered using IoT-based sensors and data loggers at key intervals. Sensors recorded the rooftop surface temperatures (for cool roofs) and ambient air temperatures (for cooling fog, shading structures, and small water paths). This analysis helped in quantifying the direct cooling effects specific to each technology and location.

• Baseline vs. Post-Installation: Data were collected continuously both before and after the technology implementations. The temperature reduction effects were measured by comparing the baseline (pre-installation) temperatures with post-installation values under similar environmental conditions. Control areas without cooling interventions were used to validate the effectiveness of each technology by isolating the impact of external factors.

• Peak Heat Hours: Special emphasis was placed on peak heat periods (typically 12:00–16:00), during which temperature reductions were most critical. For example, cooling fog and shading structures were assessed for their ability to reduce midday heat, while small water paths and cool roofs were evaluated for their overall daily temperature performance. This focus allowed for identifying the most effective cooling hours and understanding how each technology performed during extreme heat conditions.

3.3.2. Direct and Indirect Temperature Effects

• Direct Effects: The direct effects refer to the surface and ambient air temperature reductions caused by the technologies themselves. For example, cooling fog reduced ambient air temperatures in W1 (cooling fog zone) by up to 5 °C compared to W2 (sunny zone). This effect was particularly evident during midday, showing the immediate cooling potential of fog systems.

• Indirect Effects: Indirect effects were particularly relevant for cool roofs, where the impact on indoor temperatures and potential energy savings were analyzed. Buildings treated with reflective coatings not only experienced surface temperature reductions of up to 5 °C but also saw indoor temperature reductions, thereby reducing the demand for cooling. This analysis highlighted the secondary benefits of cool roofs in energy efficiency, which can provide long-term cost savings.

3.3.3. Temporal Analysis

• Daily and Hourly Trends: Temperature data were analyzed in both daily and hourly increments. For example, data collected from 27 August to 1 September 2021 in Gimhae-si showed consistent cooling effects of cool roofs during the midday heat, with peak reductions between 12:00 and 15:00. This hourly analysis allowed for capturing fluctuations and understanding how each cooling method performed across different times of the day (Figure 8).

• Day-to-Night Temperature Gaps: Additionally, nighttime temperatures were analyzed to determine the lasting effects of each cooling technology. Technologies like cool roofs and shading structures maintained lower temperatures, even after peak sunlight hours. This aspect was particularly useful for assessing the sustainability of cooling effects and understanding how long the benefits of each technology persisted after sunset.

3.3.4. Statistical Analysis

• Mean Temperature Reductions: The mean temperature reduction for each technology was calculated across the monitoring period. These reductions were averaged across multiple sites and compared to control areas without the cooling technologies. For example, the mean temperature reduction from shading structures was up to 10 °C during peak hours. These mean values provided a standardized metric for comparing the efficacy of each technology and identifying the most effective solution for urban heat mitigation (Figure 9).

• Comparison of Temperature Gaps: The temperature gaps between treated and control areas were assessed using graphical analysis (as seen in the previous figures). This was particularly relevant for small water paths and shading structures, where the difference between shaded and sunny zones varied throughout the day. Visual representations, including line graphs and bar charts, were employed to demonstrate these differences clearly, making it easier to communicate findings to urban planners and policymakers.

4. Theoretical Framework

4.1. Cool Roof (Reflective Paint) Results

The cool roof (reflective paint) experiment conducted in Gimhae-si demonstrated a significant reduction in surface temperatures on the rooftops and external walls where reflective coatings were applied. The following key results were observed:

4.1.1. Surface Temperature Reduction

The application of reflective coatings to rooftops led to a surface temperature reduction of up to 3 °C to 5 °C compared to non-applied surfaces during peak heat hours (12:00–15:00). Buildings with both cool roof and cool wall treatments exhibited the greatest surface temperature reduction, consistently staying below 40 °C, while untreated surfaces exceeded 40 °C. The combined application of cool roof and cool wall treatments (H1) produced the most significant cooling effect on both surface and air temperatures. Figure 8 illustrates that during peak heat hours (12:00–15:00), the rooftop surface temperatures of H1 consistently remained 2–3 °C lower than H2 (cool wall only) and 3–5 °C lower than H3 (non-applied). This reduction indicates that the synergy between cool roof and wall treatments minimizes solar heat absorption more effectively than a single treatment alone (Figure 8).

H1 (cool wall + roof) also showed the lowest rooftop surface temperatures, suggesting that the reflective coating on the roof effectively reduced overall heat absorption. During peak heat hours, H1 was about 2–3 °C cooler than H2 and 3–5 °C cooler than H3. This combination demonstrated a synergistic effect in reducing surface temperatures, as both reflective treatments worked together to curtail solar absorption, resulting in lower overall heat transfer.

H2 (cool wall) recorded surface temperatures higher than H1 but lower than H3, highlighting the importance of roof treatments. This suggests that while walls play a role in temperature reduction, the roof remains a critical factor in heat absorption and overall cooling. H3 (non-applied) had the highest surface temperatures, particularly during peak hours, when temperatures often exceeded 40 °C. Without reflective coatings, the roof absorbed substantial heat, leading to higher surface temperatures and increased internal and surrounding air temperatures. This comparison underscores the role of roof treatments in mitigating surface temperature elevations, even more than wall-only treatments.

4.1.2. Air Temperature Reduction

Reflective surfaces contributed to an average air temperature reduction of 1–2 °C at 1.5 m above ground level. The largest cooling effects were observed during the hottest parts of the day, demonstrating that reflective coatings can mitigate heat buildup in the surrounding environment.

H1 (cool wall + Roof) consistently showed the lowest air temperature readings at 1.5 m compared to H2 (cool wall) and H3 (non-applied). The temperature reduction was particularly noticeable during the hottest parts of the day, during which H1 remained 1–2 °C cooler than H2 and H3. This highlights the efficacy of combining both cool walls and roofs in mitigating heat buildup around buildings. H2 (cool wall) exhibited slightly higher temperatures than H1, but it was generally lower than H3 (non-applied). This suggests that applying reflective paint only to the walls provided some benefit but was less effective than when both walls and roofs were treated. H3 (non-applied) displayed the highest air temperatures, especially during afternoon peaks. This implies that without any reflective coatings, the structure absorbed and radiated more heat, leading to increased air temperatures in its vicinity.

The temperature differences among H1, H2, and H3 were most pronounced during peak heat periods (late morning to early afternoon). The cooling effect of H1 (cool wall + roof) was most significant during midday when solar radiation was highest, reinforcing the advantage of combining both cool walls and roofs for better temperature mitigation. The synergy of wall and roof treatments was especially effective in reducing the ambient heat surrounding the buildings. Nighttime temperatures for all three areas converged, as the impact of direct solar radiation diminished after sunset, reducing the temperature differences.

4.1.3. Key Observations

The surface temperatures in H1 stayed lower throughout the day, demonstrating the effectiveness of reflective coatings in keeping rooftops cool. This cooling effect likely reduced heat transfer into the building, contributing to lower indoor temperatures and enhancing thermal comfort for occupants (Figure 9).

Additionally, Figure 9 further emphasizes the temperature gap consistency over time, in which the daily temperature differences between H1 and the other sites are evident. The sustained lower temperatures in H1 suggest that combined treatments help retain a cooler surface, even under prolonged solar exposure, reducing the need for additional cooling and contributing to energy savings.

These findings are consistent with previous research, confirming that cool roofs provide both direct cooling to buildings and secondary benefits by reducing heat absorption in urban environments. H2 (cool wall), while effective in lowering wall temperatures, recorded higher rooftop surface temperatures, suggesting that a holistic approach addressing both roofs and walls is essential in heat mitigation strategies. H3 (non-applied) exhibited the poorest thermal comfort, with much higher surface temperatures contributing to increased air temperatures and heat buildup in the surrounding environment. This result underscores the need for reflective treatments in reducing urban heat island effects, particularly in high-density areas.

4.2. Cooling Fog Results in Yechun-gun

The cooling fog system installed in Yechun-gun provided immediate and noticeable reductions in ambient air temperature in the playground where it was deployed. The key findings of the experiment are as follows.

4.2.1. Cooling Fog System Effect on Air Temperature

The cooling fog system deployed in Yechun-gun demonstrated a clear and immediate reduction in ambient air temperature in the playground zone where it was activated. Prior to activation, the temperature in the cooling fog zone (W1) averaged around 35 °C, while the sunny zone (W2) averaged slightly lower at approximately 30 °C due to natural shade and airflow variations. Once the cooling fog system was activated at around 14:30, the air temperature in the W1 zone dropped sharply by approximately 1.3 °C within the first 30 min, reducing the temperature to around 28.8 °C. This rapid temperature drop highlights the system’s capacity for quick cooling, which is beneficial during peak heat periods. The cooling effect continued until around 15:00, with a total temperature reduction of 3.1 °C compared to the pre-activation phase (Figure 10).

4.2.2. Humidity Increase

In addition to temperature reduction, the cooling fog system significantly increased the relative humidity in the cooling fog zone. Before the system’s activation, the humidity in the W1 zone was stable at around 41%, similar to the humidity levels in the W2 sunny zone. Once the system was turned on, the humidity in the W1 zone rose sharply to approximately 60% during the 14:30 to 15:00 period. This 20% increase in humidity is a key contributor to enhanced thermal comfort, as higher humidity levels can make the air feel cooler, especially in dry environments. Meanwhile, the W2 zone remained stable at around 50% humidity. This shows that the fog system not only cooled the air but also increased moisture in the environment, thereby improving thermal comfort.

4.2.3. Cooling Efficiency Analysis

The analysis of the temperature difference between the cooling fog zone (W1) and the sunny zone (W2) further illustrates the cooling system’s efficiency. During the activation period, the temperature difference between the two zones widened, with W1 consistently remaining cooler by approximately 3 °C. After the system was turned off at 15:00, the temperature in W1 gradually increased, but the cooling effect lingered, maintaining a lower temperature compared to W2, indicating a residual cooling impact due to the fog system’s ability to temporarily cool surfaces and surrounding air.

The overall cooling efficiency can be summarized as follows:

• Pre-activation temperature difference: W1 was already cooler by approximately 1.8 °C due to environmental factors.

• Post-activation cooling effect: An additional 1.3 °C temperature reduction was achieved after activation, for a total cooling effect of 3.1 °C. This combined cooling effect demonstrates the fog system’s ability to reduce temperature beyond natural shading or airflow effects.

4.2.4. Key Observations

Temperature Reduction: The cooling fog system led to a significant temperature reduction in the W1 zone, with a total drop of up to 3.1 °C during its operational window (14:30–15:00). This cooling effect was observed rapidly within minutes of activation, proving the system’s immediate efficiency.

Humidity Increase: The cooling fog system increased the relative humidity in the W1 zone by approximately 20%, further enhancing the cooling sensation and improving comfort in the surrounding area. This increase in humidity is particularly beneficial in dry conditions, where added moisture can improve the perceived thermal comfort.

Extended Cooling Impact: The cooling effect was sustained even after the system was turned off, as temperatures in W1 remained lower compared to W2, suggesting that the system had a residual cooling impact. This lingering effect could be valuable for extended thermal comfort during afternoon hours, even with limited water usage.

Comparison with sunny zone (W2): While W2 experienced a steady temperature decrease due to natural conditions, it did not benefit from the sharp reduction observed in W1, indicating that the cooling fog system was the main driver of temperature reduction in W1. This comparison highlights the fog system’s unique contribution to reducing ambient temperatures more effectively than natural shading alone.

These findings confirm that the cooling fog system is an effective tool for reducing ambient air temperature and increasing humidity, especially in outdoor recreational spaces like playgrounds. This system can be particularly useful in mitigating the effects of heat during peak afternoon hours, enhancing comfort and safety for users. The data collected suggest that cooling fog systems could play an essential role in urban heat mitigation strategies, particularly in high-traffic, vulnerable outdoor spaces.

4.3. Shading Structure Results in Geyang-gu

The installation of shading structures in public spaces in Geyang-gu has shown promising results in reducing direct solar exposure and lowering air temperatures in shaded areas.

4.3.1. Shading Effect on Surface Temperature

The installation of shading structures in the public playground of Geyang-gu had a significant effect on reducing surface temperatures in the shaded area (S1) compared to the unshaded sunny area (S2). In the early morning, surface temperatures in both zones remained relatively cool, ranging between 15 °C and 20 °C (Figure 11).

As sunlight exposure increased, however, the sunny zone (S2) experienced a sharp rise in surface temperature, peaking at approximately 55 °C during midday. In contrast, the surface temperature in the shaded zone (S1) rose more gradually, with maximum temperatures reaching around 45 °C. The shading structure maintained surface temperatures in S1 at consistently lower levels, especially during the hottest hours of the day, indicating that shading structures play an essential role in mitigating solar heat gain on surfaces. The maximum observed temperature difference between S1 and S2 was approximately 10 °C.

4.3.2. Surface Temperature Reduction Efficiency

The temperature difference between the shaded zone (S1) and the sunny zone (S2) became most pronounced during the peak sunlight hours, from approximately 12:00 p.m. to 3:00 p.m. While the unshaded surfaces in S2 reached extreme temperatures of up to 55 °C, the shaded zone (S1) remained consistently cooler by about 8 °C to 10 °C.

This effect demonstrates that the shading structure not only reduces direct sunlight exposure but also plays a crucial role in lowering surface temperatures, which is critical for improving the comfort and safety of users in public playgrounds and other outdoor spaces. The shading structure’s performance was especially effective during midday, aligning with peak solar radiation and providing essential protection for vulnerable groups like children and the elderly.

4.3.3. Cooling Efficiency Analysis

The comparison of surface temperatures between the shaded zone (S1) and the sunny zone (S2) reveals the efficiency of the shading structure in mitigating heat. During peak sunlight, S2 surface temperatures spiked rapidly, while S1 surfaces increased at a much slower rate.

Throughout the day, the surface temperature difference between the two zones remained significant, particularly during the hottest parts of the day. The shaded zone (S1) consistently stayed cooler, with temperature reductions ranging from 5 °C to 10 °C compared to the sunny zone (S2). This sustained difference indicates that shading structures can provide a long-lasting cooling effect, which is vital for public spaces that remain in use throughout the day.

Summary of Cooling Efficiency:

• Pre-peak temperature difference: S1 was cooler by an average of 2 °C to 3 °C in the morning.

• Peak sunlight cooling effect: S1 surfaces were up to 10 °C cooler than S2 during peak sunlight hours.

• Overall cooling efficiency: The shading structure provided a substantial cooling effect, with up to 10 °C surface temperature reduction compared to unshaded surfaces.

4.3.4. Key Observations

• Surface Temperature Reduction: The shading structure led to a notable reduction in surface temperature within the shaded zone (S1). During the hottest part of the day, the temperature in S1 was reduced by as much as 10 °C compared to the sunny zone (S2), proving the structure’s effectiveness in moderating surface heat.

• Sustained Cooling Impact: Even after peak sunlight hours, the cooling effect in S1 persisted. The surface temperatures in the shaded zone remained significantly lower than those in the sunny zone, indicating a lasting cooling impact provided by the shading structure. This residual effect suggests that shading structures can help maintain lower temperatures even as ambient air begins to cool, extending thermal comfort for users.

• Comparison with Sunny Zone (S2): While the sunny zone (S2) experienced extremely high surface temperatures during midday (up to 55 °C), the shaded surfaces in S1 remained much cooler. This demonstrates that shading is a critical factor in reducing surface temperatures in public spaces, enhancing safety and usability for visitors, especially during extreme heat periods (Figure 12).

These results confirm that shading structures can be highly effective in reducing surface temperatures in outdoor environments, particularly during the peak hours of sunlight. This has important implications for urban heat mitigation strategies, as shading structures can play a key role in improving comfort, health, and safety in spaces designed for public use, such as playgrounds and recreational areas.

4.4. Small Water Path Results in Sangju-si

The small water path installed in Namsan Park in Sangju-si demonstrates the cooling potential of passive water features in urban parks. This installation provided continuous cooling throughout the summer, contributing both to temperature reduction and an increase in humidity levels that improved thermal comfort for park visitors.

4.4.1. Small Water Path Effect on Air Temperature

The small water path installed in Namsan Park, Sangju-si, demonstrated a continuous cooling effect on air temperature in the immediate surroundings. Initially, in the early afternoon of August 6, temperatures in both the water path zone (P1) and the sunny zone (P2) remained close, with P1 averaging approximately 35 °C and P2 averaging around 36 °C (Figure 13).

As the day progressed and the water path’s cooling influence became more apparent, P1 began to show consistently lower temperatures compared to P2. On average, the temperature in P1 was around 0.5 °C to 1 °C lower than P2 during the peak daytime hours. This cooling effect was most pronounced in the late afternoon and evening, demonstrating the water path‘s ability to moderate air temperature, particularly during the hottest periods of the day. This sustained cooling effect aligns with findings from other studies on passive water features, showing that they provide valuable temperature mitigation even as natural shading becomes limited (Figure 14).

4.4.2. Humidity Increase

In addition to reducing air temperature, the presence of the small water path led to an increase in relative humidity in the surrounding area. The humidity in the water path zone (P1) remained consistently higher than the sunny zone (P2) throughout the observation period (Figure 15).

On the morning of August 6, the humidity in P1 and P2 was relatively close, with both zones exhibiting levels between 60% and 65%. However, as the day progressed, P1 saw a sharp rise in humidity, peaking at over 90% in the late afternoon, while P2 remained slightly lower, averaging around 85%. This increase in relative humidity around the water path suggests that the feature not only cools the air but also adds moisture, which can enhance thermal comfort in dry conditions. This humidity boost is particularly important, as it contributes to a cooling sensation, making the area feel more comfortable for park visitors.

4.4.3. Cooling Efficiency Analysis

The temperature difference between the small water path zone (P1) and the sunny zone (P2) highlights the cooling efficiency of passive water features. During the observation period, P1 consistently remained cooler than P2, with the most significant temperature gap occurring in the late afternoon, when P1 was up to 1.5 °C cooler than P2.

This cooling effect was sustained through the evening, as the water path continued to moderate the air temperature. Even during peak heat, the presence of the water path prevented the air in P1 from rising as sharply as in P2, creating a more comfortable environment for park users. The sustained difference in temperature between P1 and P2 indicates that the water path can offer prolonged cooling relief, making it suitable for high-use urban parks.

Summary of Cooling Efficiency:

• Initial temperature difference: In the early afternoon, the temperature difference between P1 and P2 was minimal, with P1 being only about 0.5 °C cooler.

• Peak cooling effect: The maximum cooling effect was observed in the late afternoon, when P1 was up to 1.5 °C cooler than P2.

• Overall cooling impact: The small water path provided a consistent cooling effect, with an average temperature reduction of around 0.5 °C to 1 °C compared to the sunny zone.

4.4.4. Key Observations

• Temperature Reduction: The small water path demonstrated a significant temperature reduction effect, with air temperatures in P1 being up to 1.5 °C cooler than the sunny zone (P2) during peak sunlight hours. This cooling effect was sustained throughout the day, particularly in the late afternoon.

• Humidity Increase: The relative humidity in the water path zone (P1) was consistently higher than in the sunny zone (P2), with humidity levels in P1 reaching up to 90% during the hottest part of the day, compared to around 85% in P2. This indicates that the water path not only reduced air temperature but also increased moisture in the surrounding area, enhancing thermal comfort by creating a cooling effect through evaporation.

• Extended Cooling Impact: The cooling effect of the water path was maintained, even after peak sunlight hours, suggesting a lasting cooling impact. As temperatures in P2 began to decline naturally, P1 continued to remain slightly cooler, demonstrating the residual cooling benefit of the water path. This extended impact may be particularly valuable for evening visitors, as it provides a cooler microclimate for longer periods.

• Comparison with Sunny Zone (P2): While both zones experienced similar temperature trends throughout the day, P2 consistently showed higher temperatures, indicating that the small water path was the primary driver of the cooling effect in P1. This comparison highlights the effectiveness of water features in providing localized cooling benefits that natural conditions alone cannot achieve.

These findings confirm that passive water features, such as small water paths, are an effective tool for reducing air temperatures and increasing humidity in urban parks. These features are particularly useful for mitigating the effects of heat during peak afternoon hours, providing a more comfortable and enjoyable environment for park visitors, especially in areas frequented by vulnerable groups like children and the elderly.

4.5. Comparative Analysis of Technologies

The results demonstrated that each cooling technology provided measurable benefits in reducing temperatures and improving thermal comfort, albeit in different ways. Cooling fog and shading structures offered rapid, immediate relief in high-traffic areas, effectively reducing air temperatures in open public spaces. In contrast, cool roofs provided more sustained, long-term reductions in building surface and indoor temperatures, making them suitable for continuous-use environments. Waterway shelters, such as the small water path, offer a steady cooling effect and enhance the aesthetic and psychological experiences in urban parks.

• Temperature Reduction Comparison.

Cool Roof + Cool Wall: Combined treatments showed a 2–3 °C reduction in surface temperature during peak hours, providing the greatest cooling effect on both air and surface temperatures. Shading Structures: 2.5 °C reduction in air temperature, with a 50% reduction in solar radiation.

Cool Wall: A 1–2 °C reduction in surface temperature, demonstrating that reflective walls are effective, but less so compared to when both roofs and walls are treated.

Cooling Fog: Showed an up to 3.1 °C reduction in ambient air temperature during its operational window, making it highly effective for immediate cooling in high-traffic outdoor areas.

Shading Structures: Reduced surface temperatures by up to 10 °C during peak sunlight hours, demonstrating significant cooling potential for public playgrounds and parks.

Small Water Path: Provided a 1.5 °C reduction in air temperature during peak sunlight hours, with an additional benefit of increased humidity levels that enhanced thermal comfort (Table 7).

• Thermal Comfort and User Feedback:

All technologies contributed to significant improvements in thermal comfort. Cooling fog was particularly effective in outdoor high-traffic areas, while shading structures and small water paths were well-received in parks and public spaces. Cool roofs and walls helped to mitigate heat in and around buildings, contributing to both indoor comfort and energy savings.

These results suggest that a combination of cooling fog, shading structures, and cool roofs could be the most effective solution for mitigating heat stress in urban environments, particularly for vulnerable populations. Small water paths, while offering less dramatic temperature reductions than cooling fog, provide steady, passive cooling solutions that are aesthetically pleasing and well-received by park visitors.

5. Discussion

5.1. Interpretation of Temperature Reduction Across Technologies

The results indicate varying levels of temperature reduction across the four technologies: cool roofs, cooling fog, shading structures, and small water paths. Combined treatments, such as the cool roof + cool wall application (H1), consistently showed the most significant temperature reduction. This synergistic effect likely results from the complementary benefits of each component—while the roof coating reflects sunlight, reducing direct heat absorption, the wall coating mitigates heat transfer into indoor spaces.

5.2. Influence of Study Location Characteristics on Cooling Efficiency

The cooling efficiency of each technology varied by location and was influenced by factors such as climate, urban density, and the presence of vulnerable populations. For instance, the shading structures were most effective in densely urbanized Geyang-gu, where extensive concrete infrastructure intensifies the urban heat island effect, increasing the benefits of solar-blocking solutions. In contrast, the cooling fog system showed significant air temperature reductions in Yechun-gun, which is a predominantly rural area with high exposure to open sunlight, where added humidity also enhanced thermal comfort.

5.3. Practical Implications for Urban Heat Mitigation

These findings highlight the importance of selecting cooling technologies based on specific environmental and demographic conditions. For example, cool roofs and walls may be most beneficial in urban centers with dense infrastructure, while cooling fog and small water paths may be more suitable for recreational areas and parks because they enhance comfort for vulnerable populations. Economic factors, such as installation and operational costs, are also critical to consider, as the high initial expenses of cooling fog systems and water paths may limit their feasibility in budget-constrained areas. Additionally, maintenance requirements vary by technology; cooling fog systems, for instance, demand regular water supply and cleaning, while reflective coatings require periodic reapplication to maintain their effectiveness. Urban planners should consider these economic and operational factors to ensure the sustainability and practicality of heat mitigation strategies.

5.4. Economic, Maintenance, and Social Feasibility of Urban Heat Mitigation Technologies

5.4.1. Cooling Fog Systems

• Installation and Maintenance Costs: Cooling fog systems require relatively high initial installation costs due to specialized fogging equipment and the need for water connections. Regular maintenance includes checking nozzles for clogging, managing water flow, and ensuring overall system functionality, especially during peak use in warmer seasons.

• Operational Costs: This system incurs recurring water and electricity costs, impacting its feasibility in water-scarce regions. Studies show that the cooling efficiency may fluctuate based on environmental humidity, which could impact long-term operational costs.

• Community Acceptance: Cooling fog systems are generally well-accepted in public spaces like playgrounds and parks, as they provide immediate cooling. However, public acceptance may vary due to concerns about water waste and energy use in areas prioritizing sustainability.

5.4.2. Cool Roofs (Reflective Paint)

• Installation and Reapplication Costs: The initial application cost for reflective paint is moderate and varies depending on the roof size and specific reflective coating used. However, reapplication is required every few years, leading to cumulative costs over time.

• Maintenance Requirements: Minimal maintenance is needed, as cool roofs are designed to withstand external weather conditions. However, periodic inspections are necessary to assess coating degradation and to reapply as needed.

• Community Acceptance: Cool roofs have high community acceptance due to their passive cooling benefits and energy savings. Residents and businesses appreciate the reduced energy bills from lowered air conditioning use, but some concerns exist over aesthetic impacts, especially in historical areas.

5.4.3. Shading Structures

• Installation Costs and Maintenance: Shading structures, including canopies and pergolas, have relatively high upfront costs due to material and construction expenses. Maintenance primarily involves cleaning and occasional repairs, particularly after extreme weather events.

• Durability and Long-Term Costs: Metal or UV-resistant materials are often used to enhance durability, yet these can add to the costs. Over the long term, these structures can require repainting or reinforcement, depending on material wear.

• Community Acceptance: Shading structures are well-received in community spaces for their aesthetic and functional benefits, especially in playgrounds and outdoor dining areas. Acceptance may vary based on design, with communities preferring structures that blend with local architecture.

5.4.4. Small Water Paths

• Construction and Maintenance Costs: The construction of small water paths involves initial setup costs that vary with design complexity. Maintenance is essential to manage water quality, prevent algae buildup, and ensure continuous flow.

• Operational and Environmental Costs: Water paths have ongoing costs tied to water usage and filtration systems, which can limit their feasibility in water-scarce areas. Additionally, evaporative cooling from water paths may lose efficiency in particularly dry climates.

• Community Acceptance: Water paths are generally favored for their aesthetic value and passive cooling effects in parks. Community acceptance is high, although sustainability concerns may arise in regions experiencing water scarcity.

5.5. Social Acceptance and Long-Term Sustainability

Social acceptance of these technologies is essential for successful implementation, particularly in densely populated urban areas where public support can influence project outcomes. Cooling fog systems and shading structures are generally well-received due to their immediate visible effects, while cool roofs and reflective paint might face challenges in community buy-in due to less noticeable impact.

Long-term sustainability is another key consideration. The durability of cool roofs and reflective coatings may decrease over time, especially in areas with high pollution or extreme weather, necessitating reapplication or maintenance to retain their effectiveness. Cooling fog and small water paths, while effective in immediate cooling, also pose challenges in areas with water scarcity, potentially limiting their long-term viability in drought-prone regions. Addressing these sustainability concerns is crucial for the widespread adoption of heat mitigation technologies in urban planning.

5.6. Limitations and Directions for Future Research

While this study provides valuable insights, certain limitations should be acknowledged. The results are based on short-term observations and may not capture seasonal variations in cooling effectiveness. Additionally, future studies could explore the combined impact of multiple technologies across a wider range of environmental conditions to optimize urban cooling strategies. A more comprehensive cost–benefit analysis incorporating installation costs, maintenance requirements, and community acceptance would further refine these findings and support practical decision-making for urban planners. Long-term monitoring would also help assess durability and maintenance needs, ensuring that selected technologies remain effective and sustainable in diverse urban climates over time.

6. Conclusions and Recommendations

6.1. Conclusions

This study evaluates the performance of several urban heat mitigation technologies, including cooling fog systems, cool roofs (reflective paint), shading structures, and small water paths, with a focus on improving the thermal comfort of vulnerable populations. Field tests, which were conducted from 2021 to 2023 in collaboration with the Korean Ministry of Environment, demonstrated that each technology has unique strengths in reducing surface and ambient temperatures, improving thermal comfort, and contributing to energy savings. However, it is important to acknowledge certain limitations in this study, including the limited geographical scope and short monitoring periods for each technology. These constraints may impact the generalizability of the findings, indicating the need for further research to validate the long-term and cross-regional effectiveness of these interventions.

• Cooling Fog was one of the most effective solutions for providing immediate temperature reductions in high-traffic outdoor areas, reducing ambient temperatures by up to 3.1 °C during operational periods, which greatly improved perceived comfort.

• Cool Roofs (Reflective Paint) offered significant reductions in both surface and indoor temperatures, contributing to long-term energy savings. Buildings treated with reflective coatings experienced surface temperature reductions of 2–3 °C.

• Shading Structures provided a low-maintenance solution for mitigating solar exposure and improving thermal comfort in outdoor public spaces. Surface temperature reductions of up to 10 °C were recorded in shaded areas, particularly during peak sunlight hours.

• Waterway Shelters offered steady passive cooling, with air temperature reductions of up to 1.5 °C and humidity increases that enhanced thermal comfort for park visitors. This cooling effect was particularly noticeable in the late afternoon and evening hours.

The results suggest that a combination of these technologies can effectively mitigate heat stress in urban environments, especially for vulnerable populations, such as the elderly, children, and individuals with health conditions. By integrating active cooling technologies (such as cooling fog systems) with passive solutions (such as shading structures, cool roofs, and small water paths), cities can create more thermally comfortable and sustainable environments. Nonetheless, long-term monitoring and broader site applications are needed to confirm the durability, maintenance requirements, and year-round effectiveness of these technologies under diverse climatic conditions.

6.2. Recommendations

Based on the findings of this study, the following recommendations are proposed for urban planners, policymakers, and local governments seeking to implement effective heat mitigation strategies:

1. Adopt a Holistic Approach to Urban Heat Mitigation

Cities should integrate both active and passive cooling technologies to address heat stress across a variety of environments. Cooling fog systems should be installed in high-traffic areas, such as playgrounds, public squares, and transport hubs, whereas cool roofs and shading structures should be prioritized in areas where long-term energy savings and comfort are needed. Small water paths can be incorporated into parks and recreational spaces to provide passive cooling and enhance the aesthetic value of urban areas.

• 2.. Prioritize Vulnerable Populations in Heat Mitigation Efforts

Urban heat mitigation strategies should prioritize the protection of vulnerable populations, including the elderly, children, and low-income communities, who are disproportionately affected by extreme heat. The Korean Ministry of Environment’s initiative to fund and implement heat mitigation technologies in cities such as Yechun-gun and Sangju-si serves as a model for how local governments can support vulnerable groups through targeted interventions. Similar projects should be replicated in other regions to ensure that urban populations are protected from the adverse effects of climate change and heat waves.

• 3.. Incorporate Heat Mitigation into Urban Planning Policies

Urban planning policies should incorporate heat mitigation measures as part of broader climate adaptation strategies. Local governments should mandate the use of cool roofs in new buildings, particularly in dense urban areas, and encourage the adoption of shading structures in public spaces. Additionally, small water paths and green infrastructure should be integrated into the design of parks and public spaces to provide passive cooling solutions that are both sustainable and aesthetically pleasing.

• 4.. Monitor and Evaluate the Effectiveness of Cooling Technologies

Continuous monitoring and evaluation of cooling technologies are essential to ensure their long-term effectiveness. Data collected through IoT-based sensors and user feedback should be analyzed regularly to assess the performance of cooling systems and identify areas of improvement. Policymakers should allocate resources for ongoing research and development of heat mitigation technologies, with a focus on optimizing their effectiveness under different environmental conditions.

• 5.. Collaborate with International Cities to Share Best Practices

Given the global nature of climate change, international collaboration between cities is crucial for sharing best practices and lessons learned from heat mitigation projects. The successful implementation of heat mitigation technologies in Korea’s urban centers can serve as a valuable reference for other cities worldwide. Local governments should seek opportunities to collaborate with international partners to exchange knowledge, develop innovative solutions, and improve their resilience to extreme heat.

6.3. Future Research

While this study provides valuable insights into the effectiveness of various cooling technologies, further research is needed to explore the long-term impacts of these interventions under changing climate conditions. Future studies should focus on the following aspects:

• Long-term Monitoring: The monitoring period should be extended to assess the year-round performance of cooling technologies and their effectiveness under different seasonal conditions.

• Cost–benefit Analysis: Future studies should conduct detailed cost–benefit analyses of cooling technologies to determine the most cost-effective solutions for urban areas with varying budget constraints.

• Integration of Green Infrastructure: Research should explore how cooling technologies can be combined with green infrastructure (e.g., urban forests and green roofs) to maximize their cooling potential while enhancing biodiversity and environmental sustainability.

Author Contributions

Conceptualization, Y.-S.L. and T.K.K.; methodology, T.H.K. and T.K.K.; software, T.K.K.; validation, T.K.K.; formal analysis, T.K.K.; investigation, T.H.K.; resources, T.H.K.; data curation, T.K.K.; writing—original draft preparation, T.K.K.; writing—review and editing, Y.-S.L. and T.K.K.; visualization, T.K.K.; supervision, T.K.K. and T.H.K. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All data supporting the findings of this study are included within the article.

Conflicts of Interest

Tae Kyung Kwon was employed by the company AIRPLE. Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Footnotes

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Figures and Tables

Figure 1. Site map of Jinyeong-eup, Gimhae-si, showing cool wall and roof applications (source: Google Maps). H1 represents the cool wall + roof, H2 represents the cool wall, and H3 represents the non-applied site.

Figure 2. Site map of Yechun-gun showing cooling fog and sunny zones for comparison testing (source: Google Maps).

Figure 3. Field test site for testing the cooling fog system in Yechun-gun, with W1 representing the cooling fog zone and W2 representing the sunny zone.

Figure 4. Site map of Geyang-gu, Incheon-si, for the shadow structure applications (source: Google Maps).

Figure 5. Field test site for testing the shadow structure system in Geyang-gu, Incheon-si, with S1 representing the cool shadow zone and S2 representing the sunny zone.

Figure 6. Site map of Sangju-si for small water path applications (source: Google Maps).

Figure 7. Field test site for testing the small water path in Sangju-si, with P1 representing the small water path and P2 representing the sunny zone.

Figure 8. Comparing the 1.5M air temperatures and rooftop surface temperatures for the cool wall (top), cool wall + roof, and non-applied surfaces (bottom) during the period from 27 August to 1 September 2021. The results show significant differences in both air and surface temperatures, with the cool roof and cool wall applications reducing the surface temperature, especially during peak heat times.

Figure 9. Daily temperature gaps among H1, H2, and H3 for both air temperature (top graph) and surface temperature (bottom graph). These graphs illustrate how the gaps fluctuate over the period from 27–31 August 2021.

Figure 10. The temperature in the cooling fog zone (W1) dropped noticeably between 14:30 and 15:00, reflecting the cooling effect of the system, while the sunny zone temperature (W2) remained relatively stable (top side). The humidity in the cooling fog zone spiked during the same period, indicating the activation of the fog system, while humidity in the sunny zone remained constant (bottom side). These graphs demonstrate the immediate cooling and humidifying effect of the cooling fog system in the playground.

Figure 11. Surface temperature comparison between cool shadow zone (S1) and sunny zone (S2). As seen in the graph, the sunny zone experiences significantly higher temperature peaks compared to the cool shadow zone, particularly during daytime hours. This illustrates the impact of shading structures in reducing temperature in public spaces.

Figure 12. Temperature gap between the sunny zone (S2) and the cool shadow zone (S1) over time. The graph illustrates that during peak sunlight hours, the temperature difference can reach up to 25 °C, with the sunny zone (S2) being significantly hotter than the shaded area (S1). This demonstrates the substantial cooling effect of the shading structure, particularly during the hottest parts of the day.

Figure 13. Comparison of hourly air temperature measurements. Temperature comparison graph of the small water path (P1) and the sunny zone (P2) from 5–8 August. The data indicate that the water path (P1) consistently showed lower temperatures than the sunny zone (P2), particularly during the night and early morning hours. However, during peak daylight, the temperatures of both zones remained quite close.

Figure 14. Temperature gap between the sunny zone (P2) and the small water path (P1) from 5–8 August. The temperature difference fluctuates throughout the day, with P2 (sunny zone) generally being slightly warmer than P1 (water path), especially during the daytime. However, there are periods when P1 is briefly warmer, possibly due to local variations in air temperature.

Figure 15. Humidity comparison between the small water path (P1) and the sunny zone (P2) from 5–8 August. The small water path (P1) generally has higher humidity levels than the sunny zone (P2), especially during the late afternoon and evening hours. This shows the cooling water path‘s ability to increase moisture in the air, contributing to a more comfortable environment.

Table 1

Automatic weather station WS69 specification (source: Ecowitt, Shenzhen, China).

Measurement	Range	Accuracy	Resolution
Wind Speed	0~50 m/s	±1 m/s (speed < 10 m/s); ±10% (speed ≥ 10 m/s)	0.1 m/s
Wind Direction	0~359°	±15°	1°
Temperature	−40 °C to 60 °C	±0.3 °C (±0.6 °F)	0.1 °C (0.1 °F)
Humidity	1% to 99%	±3.5%	0.01
Light	0 Klux to 200 Klux	±25%	0.1 Klux
UVI (Ultraviolet Index)	1~15	±2	1
Rainfall	0~9999 mm	±10%	0.3 mm (volume < 1000 mm); 1 mm (volume ≥ 1000 mm)

Table 2

Field test sites, sections, addresses, and applications for cool walls and cool roofs in Jinyeong-eup, Gimhae-si.

Section	Site	Address	Application
H1	[Image omitted. Please see PDF.]	13, Jinyeongsanbok-ro 72beon-gil, Jinyeong-eup, Gimhae-si, Gyeongsangnam-do, South Korea	Cool wall + roof
H2	[Image omitted. Please see PDF.]	9, Jinyeongsanbok-ro 72beon-gil, Jinyeong-eup, Gimhae-si, Gyeongsangnam-do, South Korea	Cool wall
H3	[Image omitted. Please see PDF.]	4-1, Jinyeongsanbok-ro 72beon-gil, Jinyeong-eup, Gimhae-si, Gyeongsangnam-do, South Korea	Non-applied

Table 3

Temperature measurement sensor installation.

Section	Rooftop	Indoor	Application
H1	[Image omitted. Please see PDF.]	[Image omitted. Please see PDF.]	Cool wall + roof
H2	[Image omitted. Please see PDF.]	[Image omitted. Please see PDF.]	Cool wall
H3	[Image omitted. Please see PDF.]	[Image omitted. Please see PDF.]	Non-applied

Table 4

Field test sites, sections, addresses, and applications for cooling fog zones and sunny zones in Yechun-gun.

Section	Site	Address	Application
W1	[Image omitted. Please see PDF.]	Hancheon Sports Park166-1, Cheongcheon-ri, Yecheon-eup, Yecheon-gun, Gyeongsangbuk-do, South Korea	Cooling fog zone
W2	[Image omitted. Please see PDF.]	Hancheon Sports Park166-1, Cheongcheon-ri, Yecheon-eup, Yecheon-gun, Gyeongsangbuk-do, South Korea	Sunny zone

Table 5

Field test sites, sections, sensor installation, addresses, and applications for cool shadow zones and sunny zones in Geyang-gu, Incheon-si.

Section	Sensor Installment	Address	Application
S1	[Image omitted. Please see PDF.]	Hyo-seong Daycare Center280, Hyo-seong-dong, Geyang-gu, Incheon, South Korea	Cool shadow zone
S2	[Image omitted. Please see PDF.]	Hyo-seong Daycare Center280, Hyo-seong-dong, Geyang-gu, Incheon, South Korea	Sunny zone

Table 6

Field test sites, sections, sensor installation, addresses, and applications for small water paths and sunny zones in Geyang-gu.

Section	Sensor Installment	Address	Application
P1	[Image omitted. Please see PDF.]	Water Path Rest Area in Namsan Park3, Namsan-dong, Sangju-si, Gyeongsangbuk-do, South Korea	Small water path
P2	[Image omitted. Please see PDF.]	Water Path Rest Area in Namsan Park3, Namsan-dong, Sangju-si, Gyeongsangbuk-do, South Korea	Sunny zone

Table 7

Cooling solutions, their effectiveness in reducing temperatures, and key observations.

Cooling Solution	Temperature Reduction	Key Observation	Measurement Period
Cool Roof + Cool Wall	2–3 °C during peak hours	Combining cool roofs and cool walls showed the best reduction in surface and air temperatures.	27 August 2021–1 September 2021
Cool Wall	1–2 °C compared to non-applied surfaces	Effective for reducing wall temperatures but less effective compared to combined treatments.	27 August 2021–1 September 2021
Cooling Fog System	Up to 3.1 °C during operational window	Immediate reduction of ambient air temperature after system activation.	13 September 2021 (2:00 p.m.–4:30 p.m.)
Shading Structure	Up to 10 °C during peak sunlight	Consistent cooling effect, especially during the hottest part of the day.	30 September 2021–4 October 2021
Small Water Path	Up to 1.5 °C during peak sunlight	Moderate temperature reduction with increased humidity levels in the surrounding area.1	5 August 2023–8 August 2023

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