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The presence of water molecules in the air can impact how super cool broadband radiative coolers behave. Higher humidity in the lower atmosphere traps infrared radiation, reducing heat sent back to outer space. In this study, a mesoscale urban climate model is used to evaluate the newly developed super cool materials with broadband emissivity not selective in atmospheric window as an arsenal for urban heat management of tropical wet and dry cities like Kolkata. The results suggest that the energy balance over urban domain has substantially been altered by the city scale deployment of super cool broadband radiative cooling materials on the building rooftop. Bowen ratio and evaporative fraction values were found decreasing and increasing, respectively with a positive directional polynomial (R2 = 0.968) relationship, after the implementation of super cool broadband radiative cooling materials and in comparison, to the unmitigated scenario. At high solar hour (14:00 LT), additional thermal variables of urban domain such as 2 m air temperature, surface skin temperature, urban canopy temperature, and roof surface temperature decrease by 2.3 °C, 5.4 °C, 0.8 °C, and 31.7 °C, respectively. Reflective super cool broadband materials achieve sub-ambient temperatures up to 11.7 °C during peak hours, reduce surface wind speed by 2.5 m s−1, and lower the planetary boundary layer by 1475 m. The average daytime drop is approximately 7.3 °C, and at night, it is close to 2.4 °C. Deployment induces a "regional high" over urban areas, disrupting sea breeze onset and lowering the planetary boundary layer. Finally, an optimal cooling performance for super cool broadband radiative coolers can be achieved in lower humidity conditions, as their efficiency decreases with increased humidity. Though needing further investigation, these findings of nano-science-based super cool broadband materials offer valuable insights for policymakers and urban planners addressing thermal management in densely packed tropical urban environments. [ABSTRACT FROM AUTHOR]

The purpose of this study was to develop analytical tools to find the effectiveness of using aerosols to mitigate the urban heat island effect. Specifically, mineral calcite would be placed in a plume over cities to reflect solar radiation. A secondary goal is to compare the relative efficiencies of releasing the particles from tower heights or from aircraft heights. The aim is to reduce daytime temperatures at the surface. The method was to use a one-dimensional model or a single-column model to predict temperatures and weather conditions at all altitudes over a period of one month. The SCAM6 code was altered to incorporate the new capabilities for introduced aerosols. The pre-existing code considered only windblown dust, so the code was enhanced to handle aerosols that were intentionally produced. The key findings are that calcite as an aerosol does affect the weather. The models predict that in humid regions, calcite is less effective because it interacts with water clouds. In arid regions, calcite should be more effective since there are fewer water clouds to interact with. The result is that it is possible to predict reductions in air temperatures if solar insolation can be reduced. It was shown that temperatures can be reduced by 4 °C in arid regions. The conclusions are that calcite aerosol should be effective at mitigating urban heat islands. However, further work is needed related to economic, health, and ecological concerns. [ABSTRACT FROM AUTHOR]

Urban heat poses significant challenges in rapidly developing cities, particularly in countries like Bangladesh. This study investigates the cooling effects of urban green spaces in Rajshahi city, addressing a critical research gap in developing urban contexts. We examined the relationships among urban vegetation, heat mitigation, and temperature variables using the InVEST Urban Cooling Model and spatial analysis techniques. This study focused on three key relationships: Normalized Difference Vegetation Index (NDVI) and Heat Mitigation Index (HMI), HMI and Land Sur face Temperature (LST), and HMI and Air Temperature (AT). Analysis revealed a strong positive correlation between NDVI and HMI, indicating the effectiveness of vegetation in enhancing urban cooling. A robust inverse relationship between HMI and LST was observed (R2 = 0.78, r = −0.88), with every 0.1 unit increase in HMI corresponding to a 0.53 °C decrease in LST. The HMI−AT relationship showed an even stronger correlation (R2 = 0.84, r = −0.87), with each unit increase in HMI associated with a 2.80 °C decrease in air temperature. These findings quantify the significant role of urban green spaces in mitigating heat and provide valuable insights for urban planning in developing cities, underscoring the importance of integrating green infrastructure into urban-development strategies to combat urban heat and improve livability. [ABSTRACT FROM AUTHOR]

This study develops a quantitative method to assess the thermal usability (e.g., rideability, walkability, entertainmentability, exercisability and workability) of outdoor spaces. The benchmark for thermal usability was assessed by four widely used indicators [wet bulb globe temperature (WBGT), predicted mean vote (PMV), physiologically equivalent temperature (PET) and universal thermal climate index (UTCI)]. Among these five dimensions of thermal usability, exercisability was the most significantly thermally affected, as most of the exercise activities are moderately loaded and heavily loaded, and the exercisability of moderately loaded and heavily loaded would be lower than 33% and 24%, respectively, at WBGT above 30 °C. An empirical study based on field experiments in Changzhou, China, was performed. The results indicated that the quantitative method was capable of assessing the thermal usability of various urban spaces (e.g., basketball court, badminton field, walkway space and natural lawn), and could guide people in spatial modifications, outdoor activities and site management. The empirical studies also showed that airflow and radiation were the two critical meteorological factors, associated with urban infrastructure affecting the thermal usability of outdoor spaces. Activity metabolism showed a positive correlation with participant's heat stress and a negative correlation with the thermal usability. Suggestions were used to guide participants to avoid optional activities and to provide them protective recommendations for necessary activities during periods of low thermal usability. Overall, this paper promotes methodological understandings of thermal usability, and provides policy makers, urban planners and designers, and urban managers with implications on effective heat solutions. [ABSTRACT FROM AUTHOR]

Rapid urban expansion drives significant land cover changes, which impacts land surface temperature (LST). Understanding the trends in LST is never more relevant in the warming world. In the present study, we obtained the land use and land cover (LULC) change information over the last two decades (2000–2020) and related it with the LST, especially in the vicinity of lakes and vegetation patches. Support Vector Regression (SVR) and Locally Estimated Scatter-plot Smoothing (LOESS) non-parametric regression analyses were fit to explain the LST with the predictor variables consisting of LULC ratios in the vicinity. Results infer that SVR and LOESS models fit the observed LST with the least errors at a correlation of 0.818 and 0.816 for lakes and 0.706 and 0.712 for vegetation patches, respectively. Further, Sobol sensitivity analysis reveals that vegetation cover in the lake buffer zones plays a significant role in LST in the vicinity. Whereas vegetation, barren, and agricultural cover affects LST in vegetation buffer zones as they modify albedo, evapotranspiration, and provide shade that affects LST. The findings provide a new dimension on the role of vegetation in lake buffer areas, which significantly contributes to lowering the LST. This emphasizes re-designing nature-based infrastructure and buffer areas to reap maximum cooling benefits in the warming world. [ABSTRACT FROM AUTHOR]

This study aims at analyzing the relationships between supply of ecosystem services, features of green areas and characteristics of settlements in urban contexts, by taking the Italian city of Cagliari as study area. The services offered by the urban ecosystems that are identified as the most relevant in association with the spatial framework of green areas in urban environments are heat mitigation, carbon capture and storage, and runoff control, with particular reference to flood-related events. The features of green areas are identified with reference to the height of vegetation, by distinguishing between grasslands, shrubby cover, and trees and woodland cover. Finally, we characterize the urban settlement through the building and population densities, and through the education level, as a proxy for the residents’ social statuses. The assessment of performances of the urban ecosystem services shows negative correlations with the intensity of urbanization, whereas the size of the enhancement in the supply of ecosystem services can be associated with different types of green areas. In terms of policy implications, the outcomes of the study show that there is plenty of room for improvement in the ecosystem services performance based on fine-tuning measures which involve building and population densities and vegetation cover.

The purpose of this study was to develop analytical tools to find the effectiveness of using aerosols to mitigate the urban heat island effect. Specifically, mineral calcite would be placed in a plume over cities to reflect solar radiation. A secondary goal is to compare the relative efficiencies of releasing the particles from tower heights or from aircraft heights. The aim is to reduce daytime temperatures at the surface. The method was to use a one-dimensional model or a single-column model to predict temperatures and weather conditions at all altitudes over a period of one month. The SCAM6 code was altered to incorporate the new capabilities for introduced aerosols. The pre-existing code considered only windblown dust, so the code was enhanced to handle aerosols that were intentionally produced. The key findings are that calcite as an aerosol does affect the weather. The models predict that in humid regions, calcite is less effective because it interacts with water clouds. In arid regions, calcite should be more effective since there are fewer water clouds to interact with. The result is that it is possible to predict reductions in air temperatures if solar insolation can be reduced. It was shown that temperatures can be reduced by 4 °C in arid regions. The conclusions are that calcite aerosol should be effective at mitigating urban heat islands. However, further work is needed related to economic, health, and ecological concerns.

Urban heat poses significant challenges in rapidly developing cities, particularly in countries like Bangladesh. This study investigates the cooling effects of urban green spaces in Rajshahi city, addressing a critical research gap in developing urban contexts. We examined the relationships among urban vegetation, heat mitigation, and temperature variables using the InVEST Urban Cooling Model and spatial analysis techniques. This study focused on three key relationships: Normalized Difference Vegetation Index (NDVI) and Heat Mitigation Index (HMI), HMI and Land Sur face Temperature (LST), and HMI and Air Temperature (AT). Analysis revealed a strong positive correlation between NDVI and HMI, indicating the effectiveness of vegetation in enhancing urban cooling. A robust inverse relationship between HMI and LST was observed (R2 = 0.78, r = −0.88), with every 0.1 unit increase in HMI corresponding to a 0.53 °C decrease in LST. The HMI−AT relationship showed an even stronger correlation (R2 = 0.84, r = −0.87), with each unit increase in HMI associated with a 2.80 °C decrease in air temperature. These findings quantify the significant role of urban green spaces in mitigating heat and provide valuable insights for urban planning in developing cities, underscoring the importance of integrating green infrastructure into urban-development strategies to combat urban heat and improve livability.

In urban thermal environment research (UTE), urban shadows formed by buildings and trees contribute to significant variations in thermal conditions, particularly during the mid-day period. This study investigated the multi-scale effects of indicators, including urban shadows, on UTE, focusing specifically on the mid-day hours. It integrated field temperature measurements and drone aerial data from multiple city blocks. Considering both urban shadows and direct solar radiation, a linear mixed-effects model was employed to study the multi-scale effects of urban morphological indicators. Results showed that: (1) UTE is a multi-scale, multi-factor phenomenon, with thermal effects manifesting at specific scales. Under shadow conditions, smaller scales (10–20 m) of landscape heterogeneity and larger scales (300–400 m) of landscape consistency better explained temperature variations mid-day. Conversely, under direct sunlight, temperature was primarily influenced by larger scales (150–300 m). (2) Trees significantly reduced temperature; 100% tree canopy cover within a 10-m radius reduced air temperatures by approximately 2 °C mid-day. However, there is no significant correlation between temperature and green spaces. (3) Building area and height were significantly correlated with temperature. Specifically, an increase in building area beyond 150 m, especially within a 300-m radius, leads to higher temperatures. Conversely, building height within a 10–20 m range exhibits significant cooling effects. These findings provide crucial reference data for micro-scale UTE investigations during mid-day hours and offer new strategies for urban planning and design. [ABSTRACT FROM AUTHOR]

Due to urban warming, the energy demand for cooling buildings is rising. The current study used CitySim (building energy model) to estimate the cooling energy requirements for 40 buildings in downtown Dubai using high-resolution climate data from weather research and forecasting (WRF) coupled with the single layer urban canopy model (SLUCM). Simulating the four mitigation scenarios allowed for the examination of the reduction in cooling load caused by the addition of greenery at a rate ranging from 25% to 100%. The insulated building's cooling demand reduced by a maximum of 13.89% under 100% GI (M4). Scenario M4 resulted in a reduction of 4.6 kWh/m2 and 3.1 kWh/m2 for the non-insulated and insulated low-rise residential buildings, respectively, while the high-rise buildings saw a reduction of 3.09–4.91 kWh/m2 for the non-insulated and 2.07–3.09 kWh/m2 for the insulated buildings. This study offers a potential remedy to deal with the problem of urban heating in subtropical environments. [ABSTRACT FROM AUTHOR]

This study aims at analyzing the relationships between supply of ecosystem services, features of green areas and characteristics of settlements in urban contexts, by taking the Italian city of Cagliari as study area. The services offered by the urban ecosystems that are identified as the most relevant in association with the spatial framework of green areas in urban environments are heat mitigation, carbon capture and storage, and runoff control, with particular reference to flood-related events. The features of green areas are identified with reference to the height of vegetation, by distinguishing between grasslands, shrubby cover, and trees and woodland cover. Finally, we characterize the urban settlement through the building and population densities, and through the education level, as a proxy for the residents' social statuses. The assessment of performances of the urban ecosystem services shows negative correlations with the intensity of urbanization, whereas the size of the enhancement in the supply of ecosystem services can be associated with different types of green areas. In terms of policy implications, the outcomes of the study show that there is plenty of room for improvement in the ecosystem services performance based on fine-tuning measures which involve building and population densities and vegetation cover. [ABSTRACT FROM AUTHOR]

Urban vegetation is a nature-based solution for cooling cities. Under global warming and urban population growth, it is essential to optimize urban vegetation configuration in the urban area to bring maximum cooling benefit. This paper reviews 85 optimized urban vegetation configuration studies published from 2010 to 2020 to provide an insight into the most effective vegetation configuration for urban heat mitigation. Patterns and preferences in methods and the optimized greenery configurations are comprehensively analyzed. The results indicate that size, quantity, and layout of urban green space and the physiological characteristics and spatial arrangement of urban vegetation significantly influence their cooling effect. Additionally, two other research gaps were identified. First, more research needs to be done in southern hemisphere cities experiencing rapid urbanization and severe impacts of extreme weather. Second, a comprehensive method for quantifying interactions and cumulative effects of natural and artificial factors in the urban environment is required. Future study needs a holistic understanding of the interactive effects of vegetation spatial distribution on urban environment and climate for a more accurate analysis of optimal cooling greening layouts in large urban areas at multi-scales.

The present study examines the temporal and spatial variability of near‐surface air temperature and the canopy layer urban heat island (UHI) in Singapore. Observations collected at 20 locations across the island city‐state and during 6 years make this one of the most extensive studies carried out in a tropical city. Local climate zones (LCZs), defined as urban built and rural land cover types which produce a unique air temperature response, are used to standardize intersite comparison. The results show that the choice of the rural reference can affect the night‐time UHI magnitude by up to 2°C under "ideal" (dry, clear, calm) conditions. The most frequently observed median UHI magnitude increases from 2.8 during all‐weather to 3.7°C during "ideal" conditions, respectively. A seasonality is present with lowest (highest) mean all‐weather values of ~2.0°C (~3.3°C), observed during the wet (dry) December–January (April–October) period. Mean night‐time UHI intensity across seven built‐type LCZs ranges between 1.8 and 3.5°C (2.5 and 4.3°C) for all‐weather ("ideal") conditions. Corresponding daily values are 1.1–2.3°C (1.5–2.7°C). The lowest (highest) night‐time magnitudes are associated with open low‐rise LCZ 6 (compact high‐rise LCZ 1) built type. In the middle of the day LCZ 1 can experience a cool island effect. The average UHI values presented here give an indication of the extra warmth experienced in the built‐up spaces of Singapore relative to one possible rural reference land cover type (scattered trees LCZ B). Highest daytime heat exposure is observed in LCZs 3 and 8 which are characterized by low building heights, high impervious surface fraction and lack of vegetation. The present results can be used to support the development and evaluation of urban climate models, develop urban planning policies and improve local weather forecasts and the delivery of integrated urban services. [ABSTRACT FROM AUTHOR]

• Thermal impacts of urban elements were comprehensively evaluated by sub-meter data. • Key spatial factors with their marginal effects on LST were identified by RF model. • Complex built context cools more than homogeneous landscape due to increased shade. • High-resolution UAV observations offer new insights for effective cooling designs. • Diversified strategies were integrated in a prioritized manner for LST mitigation. Widespread utilization of satellite infrared observations has revealed potential urban morphology designs to mitigate surface urban heat island effect. However, studies towards holistic thermal effects of internal and external spatial attributes on built-up areas are limited. Moreover, the use of low-resolution thermal pixels for hybrid landscape components introduce uncertainty in deriving effective cooling strategies. Here, we obtained submeter-level land surface temperature (LST) maps and spatial datasets using an unmanned aerial vehicle and comprehensively evaluated impacts of urban characteristics on LST during a hot summer day. The results of a random forest model indicated that 2D landscape composition had the strongest thermal contribution at block scale. Conversely, at fine-scale impervious activity space, 3D spatial configuration governed daytime LST, and the identified crucial influencing metrics represented by sky view factor exhibited non-linear correlations with LST. Accordingly, shade casting was a core mechanism through which 3D elements collectively contributed to outdoor heat dissipation, more efficient than effects of surface materials and their optical properties. Furthermore, regarding uncertain exogenous thermal impact of large blue–green spaces, no significant cooling effects were detected on adjacent built-up surfaces. These findings provided prioritized insights on how to integrate diverse urban elements to effectively reduce outdoor heat stress. [ABSTRACT FROM AUTHOR]

• Evaluating the cooling capacity of BGIs on urban thermal environment in Kolkata. • Two cooling indexes i.e. park cooling area & park cooling efficiency were used. • Randon forest and XAI were applied for examining influencing factors on BGIs. • Spatial configurations of BGIs strongly influence cooling capacity. • Study advocates for increasing BGIs in cities for improving urban environment. Urban blue-green infrastructures (BGIs) have a considerable cooling effect, reducing the urban heat island effect. Therefore, this study aims to evaluate the cooling effects of BGIs and role of the influencing factors on urban thermal environment in Kolkata city, which is one of the largest mega cities of India. An integrated radius and non-linear regression approach was used to determine the maximum distance over which cooling is effective. Further, the relationship between cooling effects of BGIs and influencing factors was analysed using Random Forest based Explainable artificial intelligence model. The result shows that for most of the BGIs, the range of maximum cooling distance varies from 210 to 240 m from the boundary of BGIs. The average PCA value ranges from 6.12 to 16.77 hectares and PCE value ranges from 1.62 to 2.87 depending of BGIs. The results of PCA, PCE and maximum cooling distance indicate that the spatial configurations of BGIs and landscape pattern within and surrounding of BGIs sites strongly influence the cooling effects. The outcomes of this study provide valuable insights for the policymakers and urban planner about the intervention of blue-green infrastructures for the better urban environmental conditions and heat mitigation in mega cities and other urban areas. [ABSTRACT FROM AUTHOR]

In urban thermal environment research (UTE), urban shadows formed by buildings and trees contribute to significant variations in thermal conditions, particularly during the mid-day period. This study investigated the multi-scale effects of indicators, including urban shadows, on UTE, focusing specifically on the mid-day hours. It integrated field temperature measurements and drone aerial data from multiple city blocks. Considering both urban shadows and direct solar radiation, a linear mixed-effects model was employed to study the multi-scale effects of urban morphological indicators. Results showed that: (1) UTE is a multi-scale, multi-factor phenomenon, with thermal effects manifesting at specific scales. Under shadow conditions, smaller scales (10–20 m) of landscape heterogeneity and larger scales (300–400 m) of landscape consistency better explained temperature variations mid-day. Conversely, under direct sunlight, temperature was primarily influenced by larger scales (150–300 m). (2) Trees significantly reduced temperature; 100% tree canopy cover within a 10-m radius reduced air temperatures by approximately 2 °C mid-day. However, there is no significant correlation between temperature and green spaces. (3) Building area and height were significantly correlated with temperature. Specifically, an increase in building area beyond 150 m, especially within a 300-m radius, leads to higher temperatures. Conversely, building height within a 10–20 m range exhibits significant cooling effects. These findings provide crucial reference data for micro-scale UTE investigations during mid-day hours and offer new strategies for urban planning and design.

Due to urban warming, the energy demand for cooling buildings is rising. The current study used CitySim (building energy model) to estimate the cooling energy requirements for 40 buildings in downtown Dubai using high-resolution climate data from weather research and forecasting (WRF) coupled with the single layer urban canopy model (SLUCM). Simulating the four mitigation scenarios allowed for the examination of the reduction in cooling load caused by the addition of greenery at a rate ranging from 25% to 100%. The insulated building’s cooling demand reduced by a maximum of 13.89% under 100% GI (M4). Scenario M4 resulted in a reduction of 4.6 kWh/m2 and 3.1 kWh/m2 for the non-insulated and insulated low-rise residential buildings, respectively, while the high-rise buildings saw a reduction of 3.09–4.91 kWh/m2 for the non-insulated and 2.07–3.09 kWh/m2 for the insulated buildings. This study offers a potential remedy to deal with the problem of urban heating in subtropical environments.

Urban greening is attracting considerable research and practical attention for its contributions to conserving biodiversity, mitigating urban heat and enhancing the liveability and sustainability of cities and urban areas. Much of the urban greening research is concentrated on major cities, with little focus on the needs and experiences with urban greening in regional cities and towns. This paper addresses this by presenting a case study of an urban greening project, 'Naturally Cooler Towns', focused on regional towns in north-east Victoria, Australia. The project was undertaken by the Goulburn Murray Climate Alliance, a regional alliance of local governments, catchment management authorities and a state government department. As the region faces increasing temperatures and impacts of more frequent heatwaves, the project aimed to review tree management practices and identify opportunities for increasing canopy cover with appropriate species for 'climate adapted street trees'. We examine how urban greening is planned and implemented in these towns, and the roles of the regional alliance in providing a forum for collaborative adaptive governance. The regional alliance plays a key role as an intermediary facilitating approaches that demonstrate situatedness: credibility, salience and legitimacy. The paper contributes towards increased understandings of urban greening approaches beyond the major cities. [ABSTRACT FROM AUTHOR]

Urban vegetation is a nature-based solution for cooling cities. Under global warming and urban population growth, it is essential to optimize urban vegetation configuration in the urban area to bring maximum cooling benefit. This paper reviews 85 optimized urban vegetation configuration studies published from 2010 to 2020 to provide an insight into the most effective vegetation configuration for urban heat mitigation. Patterns and preferences in methods and the optimized greenery configurations are comprehensively analyzed. The results indicate that size, quantity, and layout of urban green space and the physiological characteristics and spatial arrangement of urban vegetation significantly influence their cooling effect. Additionally, two other research gaps were identified. First, more research needs to be done in southern hemisphere cities experiencing rapid urbanization and severe impacts of extreme weather. Second, a comprehensive method for quantifying interactions and cumulative effects of natural and artificial factors in the urban environment is required. Future study needs a holistic understanding of the interactive effects of vegetation spatial distribution on urban environment and climate for a more accurate analysis of optimal cooling greening layouts in large urban areas at multi-scales. [ABSTRACT FROM AUTHOR]

The urban heat island (UHI) effect is one of the most critical issues for dense urban environments; building forms and facades increase this effect and building energy use intensity (EUI). This research hypothesizes that by using a design-based approach, a new generation of climate-responsive building forms and facades can be developed that balance the outdoor and indoor environments and minimize the UHI effect. A novel design workflow is proposed to integrate UHI mitigation strategies, urban microclimate simulation methods, and building performance optimization techniques during the early stages of the architectural design process, employing elements such as parametric modeling and objective optimization. As a proof of concept, redesigning a 56-storey core and shell office tower in downtown Chicago, IL is found to improve outdoor thermal comfort by up to 1.26°C, EUI by 0.79 kWh/m2, and unusable daylight by 50.90%, as compared to the existing design. [ABSTRACT FROM AUTHOR]

[Display omitted] • Regional climate change intensifies urban heat and boosts cooling energy use in desert cities. • Simulation results using WRF/SLUCM data in CitySim for diverse mitigation scenarios demonstrate their efficacy. • Results showed a 17.2% to 36.4% drop in cooling energy demand for non-insulated buildings, while insulated buildings saw a reduction of 15.5% to 29.1%. • Combined mitigation techniques yield greater reductions in cooling energy consumption compared to individual methods such as increased urban vegetation or modiefied urban materials. Regional climate change leads to more extreme urban heat in desert cities. This affects the building's performance negatively through an increase in cooling energy consumption. To our knowledge, this is the first study investigating the impacts of implementing combined urban heat mitigation strategies of cool materials and increased vegetation on the cooling load demands of 40-various types of buildings in Dubai downtown. Four urban heat mitigation scenarios have been conducted in combination with a base case scenario to examine the effectiveness of the combined strategies in reducing the cooling load demand by using the climatic data from weather research and forecasting model coupled with single layer urban canopy model (WRF/SLUCM) in CitySim. Results revealed that for non-insulated buildings there was an estimated 17.2% to 36.4% reduction in cooling energy demand whereas insulated buildings have an average reduction in energy demand ranging between 15.5% and 29.1%. This reduction in cooling energy consumption is higher when compared with other mitigation techniques like additional urban vegetation and modified cool materials. [ABSTRACT FROM AUTHOR]

Enhancing the cooling effectiveness of green spaces (GSs) is crucial for improving urban thermal environments in the context of global warming. Increasing GS coverage and optimizing its spatial distribution individually proved to be effective urban cooling measures. However, their comparative cooling effectiveness and potential interaction remain unclear. Here, using the moving window approach and random forest algorithm, we established a robust model ( R = 0.89 ± 0.01) to explore the relationship between GS and land surface temperature (LST) in the Chinese megacity of Guangzhou. Subsequently, the response of LST to varying GS coverage and its spatial distribution was simulated, both individually and in combination. The results indicate that GS with higher coverage and more equitable spatial distribution is conducive to urban heat mitigation. Increasing GS coverage was found to lower the city's average LST by up to 4.73 °C, while optimizing GS spatial distribution led to a decrease of 1.06 °C. Meanwhile, a synergistic cooling effect was observed when combining both measures, resulting in additional cooling benefits (0.034-0.341 °C). These findings provide valuable insights into the cooling potential of GS and crucial guidance for urban green planning aimed at heat mitigation in cities. 2 = 0.89 ± 0.01) to explore the relationship between GS and land surface temperature (LST) in the Chinese megacity of Guangzhou. Subsequently, the response of LST to varying GS coverage and its spatial distribution was simulated, both individually and in combination. The results indicate that GS with higher coverage and more equitable spatial distribution is conducive to urban heat mitigation. Increasing GS coverage was found to lower the city's average LST by up to 4.73 °C, while optimizing GS spatial distribution led to a decrease of 1.06 °C. Meanwhile, a synergistic cooling effect was observed when combining both measures, resulting in additional cooling benefits (0.034-0.341 °C). These findings provide valuable insights into the cooling potential of GS and crucial guidance for urban green planning aimed at heat mitigation in cities.

Tree-induced cooling benefits are associated with various factors, such as canopy morphology, surface cover, and environmental configuration. However, limited studies have analyzed the sensitivity of tree-induced cooling effects to the combination of such factors. Most studies have focused on 1.5-m cooling performance, and few studies on the variability of the under-tree vertical cooling performance. Therefore, this study aims to investigate the vertical cooling performance of different combinations of trees and surface covers. The study was completed in Chongqing, China, with field experiments capturing vertical air temperature and wind speed at 0.5, 1.0, 1.5, 2.0 and 2.5 m under two typical combinations of "tree + grass" (ComA) and "tree + shrubs" (ComB), and capturing 1.5 m microclimatic environments of a control group with hard pavement without tree shade (REF). The results show that at an average ambient temperature of 33 °C, the maximum air-cooling temperatures for ComA and ComB were 2.46 °C and 1.78 °C, respectively. An increase in the ambient temperature corresponded to a decrease in the cooling effect difference between ComA and ComB. ComA had a maximum vertical temperature difference of 1.01 °C between H 1.5m and H 2.0m. Between H 2.5m and H 2.0m , the maximum vertical temperature difference for ComB was 1.64 °C. This study explored the changing patterns of under-tree vertical temperatures under different tree and surface cover combinations, conducive to clarifying the key elements affecting tree cooling performance. The results have implications for accurate thermal comfort assessments and provide a theoretical basis for fine-tuning the design of under-tree spaces. • Cooling performance of tree-surface combinations was compared with bare surface. • Vertical cooling performance of tree-surface combinations were revealed. • Tree-grass had better cooling potential than tree-shrub. • The maximum vertical temperature gap in specific combinations is larger than 1 °C. • The results can generate implications on accurate thermal comfort assessment. [ABSTRACT FROM AUTHOR]

To counter the increasing urban overheating, climate adaptation solutions are proposed. Among them, water mist spray recently acquired particular attention, due to its efficiency, cost-effectiveness, and versatility. However, spray devices require a large amount of water and energy to cool even limited areas, thus their environmental costs/benefits ratio should be carefully evaluated. This study analyses cooling benefits and resources consumption of mist devices in 11 cities within 3 climate contexts, through Recurrent Neural Networks (RNNs) trained with experimental data. RNNs predict the expected time series of thermal benefits and of energy and water consumptions, also considering different design solutions of devices. Results show that when sun/wind shielding is used in the sprayed area, or the height of nozzles is limited, higher cooling results are obtained. However, energy and water consumption are extremely high if misting systems are perennially active during the day. Considering all simulated conditions, the predicted average daily energy to obtain a unitary variation of the Mediterranean Outdoor Comfort Index is 4,17 Wh/m2, while the corresponding average daily volume of water is 0,56 l*h/m2. These results confirm the need for applications managed by control logics based on the acquisition of real-time climatic data to reduce the environmental loads. [ABSTRACT FROM AUTHOR]

Infrastructure-based heat reduction strategies can help cities adapt to high temperatures, but simulations of their cooling potential yield widely varying predictions. We systematically review 146 studies from 1987 to 2017 that conduct physically based numerical modelling of urban air temperature reduction resulting from green-blue infrastructure and reflective materials. Studies are grouped into two modelling scales: neighbourhood scale, building-resolving (i.e. microscale); and city scale, neighbourhood-resolving (i.e. mesoscale). Street tree cooling has primarily been assessed at the microscale, whereas mesoscale modelling has favoured reflective roof treatments, which are attributed to model physics limitations at each scale. We develop 25 criteria to assess contextualization and reliability of each study based on metadata reporting and methodological quality, respectively. Studies have shortcomings with respect to neighbourhood characterization, reporting areal coverages of heat mitigation implementations, evaluation of base case simulations, and evaluation of modelled physical processes relevant to heat reduction. To aid comparison among studies, we introduce two metrics: the albedo cooling effectiveness (ACE), and the vegetation cooling effectiveness (VCE). A sub-sample of 47 higher quality studies suggests that high reflectivity coatings or materials offer ≈0.2 °C–0.6 °C cooling per 0.10 neighbourhood albedo increase, and that trees yield ≈0.3 °C cooling per 0.10 canopy cover increase, for afternoon clear-sky summer conditions. VCE of low vegetation and green roofs varies more strongly between studies. Both ACE and VCE exhibit a striking dependence on model choice and model scale, particularly for albedo and roof-level implementations, suggesting that much of the variation of cooling magnitudes between studies may be attributed to model physics representation. We conclude that evaluation of the base case simulation is not a sufficient prerequisite for accurate simulation of heat mitigation strategy cooling. We identify a three-phase framework for assessment of the suitability of a numerical model for a heat mitigation experiment, which emphasizes assessment of urban canopy layer mixing and of the physical processes associated with the heat reduction implementation. Based on our findings, we include recommendations for optimal design and communication of urban heat mitigation simulation studies.

By enhancing evapotranspiration (ET), green roofs provide cooling benefits for the urban environment and are recognized as a promising heat mitigation strategy. The evaporative cooling effects of green roofs strongly depend on the soil moisture conditions and thus irrigation may be needed to sustain the cooling benefits. It has been shown that the magnitude of cooling benefits offered by green roof irrigation varies spatially, but its controlling factors remain elusive. In this study, we combine a surface energy balance (SEB) model with global simulations generated by an improved Earth System Model to illustrate the key factors controlling the cooling benefits of green roof irrigation. We employ a simple irrigation scheme, which is only active when there is no ice in soil layers and when the soil moisture is below field capacity. As a result, most of the irrigation water leaves the green roof system via ET. We find that the magnitude and also the spatial variability of the cooling benefits of green roof irrigation are controlled by the irrigation amount, and a surface energy redistribution factor that encodes the efficiencies of different SEB components in transferring heat. Further analysis indicates that the enhancement of latent heat flux due to irrigation is largely balanced by the reduction of sensible heat flux on green roofs. Therefore, the amount of irrigation needed per unit decrease of green roof surface temperature is mainly controlled by the convective heat transfer efficiency. A lower convective heat transfer efficiency (e.g. under a lower wind speed) helps reduce the amount of irrigation needed per unit decrease of green roof surface temperature. This study highlights the importance of SEB in constraining the cooling benefits of green roof irrigation and provides valuable guidance for urban planners and policy makers in terms of heat mitigation and sustainable water management.

Municipalities often consider heat mitigation strategies to address urban overheating, but the location of implementation rarely is co-located with the communities that are carrying the majority of the heat burden in the city. The City of Phoenix, is redeveloping a public housing community with a focus on urban cooling as a desired outcome. This research uses in situ measurements (including the mobile micro-meteorological measurement cart, MaRTy) and ENVI-met microscale modeling of the neighborhood to assess air temperature (T air) cooling capabilities of the planned redesigns to the neighborhood. After validating the ENVI-met model of the current neighborhood with fixed and mobile measurements with an index of agreement d > 0.9 and d > 0.8, respectively, analysis of the planned urban design shows some cool spots connected to new shade and vegetated corridors with T air cooling magnitudes as high as 3 °C. Yet, some exposed and building-adjacent areas were identified as potential hot spots in the planned neighborhood. These hotspots underscore the importance of continued collaboration among the City, researchers, and the community to address the needs of the community for the creation of healthier urban environments. • ENVI-met was validated using fixed and mobile measurements of air temperature • Redesign plans with increasing tree canopy reduce T air by up to 1.5 °C • Localized cooling resulted from increased building heights and tree canopy • Thermal equity may be increased via evidence-based design linked to community need [ABSTRACT FROM AUTHOR]

[Display omitted] • 167 studies on UGS configuration and cooling effect using LMs were reviewed. • Diverging suggestions on UGS configuration at patch and class level exist. • Contextual and methodological factors cannot help interpret the diverging suggestions. • Few specific planning and design implications on UGS configuration were given. • Future directions for better implications to UGS planning and design are discussed. Urban green spaces (UGS) are effective mitigations to excessive urban heat. Landscape metrics (LMs) have been widely used to assess how UGS configuration, i.e., edge and area, shape complexity, and aggregation, may facilitate better cooling. However, application of configurational LMs has produced diverging suggestions for planning and design practice, which cannot provide urban and landscape designers with holistic insights for future sustainable development. Thus, we conducted a systematic review to (1) summarize the contextual and methodological factors in pertinent studies, and (2) synthesize extractable results and implications, and see if the contextual and methodological factors may help to interpret the diversity in planning and design implications. A total of 167 studies were identified, covering 90 cities in 27 countries belonging to 16 Köppen climate zones. Evolving statistical methods have been applied, including spatial, non-spatial, and non-parametric machine-learning analyses. Synthesis of correlation coefficients reveals that patch-level metric SHAPE, and class-level metrics LPI, AI and COHESION yielded generally consistent trends across studies. No consensus was obtained based on patch-level metrics, while class-level analyses suggest aggregated, patchy, larger, and complex-shaped UGS facilitate better cooling. Contextual and methodological factors cannot help interpret the diverging suggestions. Few specific planning and design implications on UGS configuration were given. Future studies are suggested to specify either a land-use or land-cover perspective to align with practical scales in planning and design practice, and to formulate specific implications beyond binary suggestions by echoing the heterogeneity of thermal environment and UGS pattern under precise planning and design contexts with practical illustration. [ABSTRACT FROM AUTHOR]

Urban areas are experiencing excessive heating. Addressing the heat is a challenging but essential task where not only engineering and climatic knowledge matters but also a deep understanding of social and economic dimensions. We synthesize the state of the art in heat mitigation technologies and develop an 'ITE index' framework that evaluates the i nvestment (I), t ime for implementation (T), and e ffectiveness (E) of candidate heat mitigation measures. Using this framework, we assess 247 multimeasure-centric solution sets composed of all possible combinations of 8 individual measures. The multidimensional ITE index is quantified for heat mitigation effectiveness based on different urban scales, investment levels, the impact of local climate zones (LCZs), and professionals' perceptions using the analytical hierarchy process. The top 50 unique solution sets consist of 4–7 individual measures across all LCZs, with the use of thermally efficient buildings and high-efficiency indoor cooling being the two recurrent measures contributing to the best solution sets. While every city varies in terms of its ideal solution sets, we provide a multimeasure-centric framework for decision-making in which different dimensions can be integrated, understood, and quantified. [Display omitted] • We propose and assess 247 multimeasure-centric solution sets. • Eight individual measures at the building and neighborhood scales are combined. • An 'ITE index' framework is proposed to evaluate multimeasure-centric solution sets. • Decision-making focuses on i nvestment, t ime for implementation, and e ffectiveness. • By taking a whole-system approach, costs and effectiveness can be balanced. [ABSTRACT FROM AUTHOR]

At present, and motivated by a substantial growth of the population, a considerable expansion of urban areas is taking place through the modification of land uses. These changes, together with global warming and extreme weather events, produce increases in the temperature of the earth's surface and a deterioration of the environment that affects people's quality of life. The green areas of cities are upheld as one of the best for adapting to such phenomena, since they help lower outdoor temperatures. In this research, using high-resolution Sentinel 3 satellite images and the TsHARP algorithm, the Land Surface Temperature (LST) and the Park Cool Island (PCI) were obtained at a resolution of 10 m over green areas in the city of Granada. The objective was to analyze the relationship between surface, PCI effect and cooling distance. In turn, for each of the eight green areas studied, the following variables were taken into account and included in a statistical analysis known as data panel: normalized difference vegetation index, vegetal proportion, sky view factor, landscape shape index, model digital elevation, wind and solar radiation. Our results report diurnal LST decreases of 1 K and night LST of 0.6 K in green areas as compared to urban areas. There is moreover a correlation between the size of the green areas, the decrease in temperature they generate, and distance of the minimizer effect. • A diurnal reduction of 1 K is reported in green areas compared to urban areas. • A nocturnal reduction of 0.6 K is reported in green areas compared to urban areas. • A negative correlation is reported between the surface of the green zone and the decrease in temperature. • The distance of minimization of the daytime PCI has been between 30 and 150 m. • The night PCI minimization distance has been between 60 and 120 m. [ABSTRACT FROM AUTHOR]

Abstract: The rapid urbanization and associated landscape changes strongly modulate heat and moisture transfer processes on the urban surface as well as in the planetary boundary layer (PBL) via urban land‐atmosphere interactions. In this study, we employed the mesoscale Weather Research and Forecasting (WRF) model with realistic urban dynamics to assess the effects of two urban landscaping strategies for urban heat mitigation (viz., green roofs and white roofs) on the PBL dynamics for hot summer periods over a semiarid city, Phoenix of Arizona. Our results show that the effects of green roofs and white roofs on PBL dynamics are markedly different at daytime and nighttime. At daytime, both roofing systems reduce the sensible heat flux significantly by ~150 W/m2, lower the PBL height by ~700 m, and decrease the maximum convective available potential energy (CAPE) by ~40 J/kg over the built terrain. At nighttime, both sensible and latent heat fluxes increase with green roofs by ~4 and ~6 W/m2, respectively. In contrast, with white roofs, a marginal reduction of sensible heat flux by ~4 W/m2 was observed, owing to the remnant effect of daytime cooling. In addition, both roofing systems reduce the CAPE over the urban core but increase the CAPE over the rural surrounding, implying that the use of green or white roofs may potentially enhance the probability of precipitation toward the outskirt of the city. [ABSTRACT FROM AUTHOR]

The combined trends of urban heat island intensification and global warming are focusing attention on greening of cities as a tool for urban heat mitigation. Our study examines the range of research approaches and findings regarding the role of urban green infrastructure (UGI) in mitigating urban heat and enhancing human comfort. It provides an overview based on 89 studies, carried out in a range of geographic and climatic regions. We surveyed the distribution of methodologies employed, spatio-temporal scales considered, type and extent of UGI, climatic variables studied and contribution of UGI to ambient air cooling and enhancement of human comfort. It was found that neither the differences in geographic location or in climate conditions had a significant impact on the choice of research approach. The studies, mostly done on limited spatio-temporal scales, have focused on the rate of air cooling by UGI, and to a lesser extent on its impact on thermal comfort. Maximum observed intensities of park cool island (PCI) effects typically ranged between 1.5 °C–3.5 °C, with no apparent correlation to climatic region. However, there is a tendency seen for larger green sites to induce a stronger PCI, whereas well-shading street trees also have a significant cooling and relieving effect. [ABSTRACT FROM AUTHOR]

The emergence of integrated urban water management (IUWM), provides a unique opportunity for passive evaporative cooling of urban environments. This study investigates the potential of purposefully managed irrigation for cooling benefits in a suburb of Adelaide, Australia, where IUWM is widely adopted. SURFEX was used to simulate heatwave conditions across a suburban environment. Results from two simulation periods are presented: model validation period and a heatwave case study. Model validation suggests SURFEX can broadly capture the average intra-suburban diurnal air temperature variability, but not the average maxima and minima. A range of idealised irrigation scenarios were tested with different rates and timing of watering implemented. Clear evidence was found that irrigation reduces air temperature in urban environments. The diurnal average air temperature was reduced by up to 2.3 °C. The cooling benefit of increasing irrigation was non-linear, with negligible additional cooling predicted above 20 L m −2 d −1 . The magnitude of cooling was proportional to the pervious (irrigated) fraction, meaning less cooling occurred in areas with greater urban development. Although irrigation increased humidity, it still improved outdoor human thermal comfort during heatwave conditions. IUWM approaches can provide an additional fit-for-purpose water supply to the urban environment, which should be utilised for cooling benefits. [ABSTRACT FROM AUTHOR]

Urban morphology affects the sensible heat flux and net radiation exchange which can alter urban heat mitigation plans. This study first parameterized the geometric effects on the net radiation, and then calculated the net radiation and sensible heat flux in the urban landscape of Hong Kong. Considering that the sensible heat flux is the main heat sink in compact urban areas, this study proposes a Normalized Urban Sensible Heat Mitigation Index (NUSHMI) based on the ratio of the net radiation and sensible heat flux. Overall, there is major difference in the dependence of net radiation and sensible heat flux on geometric parameters. Net radiation Rn, reaches an optimal value, either maximum or minimum depending on the parameters of SVF and a standard deviation of building height σ h , at intermediate parameter values, which suggests a guideline relevant to urban design targeting the mitigation of urban climate. Contrariwise, sensible heat flux decreases or increases, again depending on SVF and σ h , is being considered, with increasing values of the same parameters. For example, R n , reaches a minimum value for a Sky View Factor (SVF) between 0.5 and 0.6, while it reaches a maximum value for a standard deviation of building height σ h between 20 and 30 m. These two results suggest that radiative forcing, i.e. R n , can be minimized by urban space with SVF around 0.55 and σ h around 25 m. The relationships between sensible heat flux and SVF or σ h do not show multiple minima or maxima (as with R n), with the exception of building density, which could also be applied as a guideline in urban design. The results based on the proposed NUSHMI indicated the NUSHMI reaches the highest values when building density is about 0.7 and building height is about 80 m and when the building height standard deviation within an area is about 10 m to 20 m. These findings revealed how the urban morphology affects the surface heat flux exchange between urban canopy and atmosphere boundary layer, and can help to design an efficient urban landscape towards urban heat mitigation for highly compacted cities, e.g. controlling the building density, height, and the height deviation. This combination of urban geometric parameters identifies an urban configuration maximizing the dissipation of absorbed radiant energy as sensible heat. It should be noted, however, that heat load upon buildings would be reduced at the price of maximizing heat dissipation within the built-up space. • This study first parameterized the geometric effects on the net radiation. • NUSHMI is defined as the ratio of the net radiation and sensible heat flux. • Sensible heat flux and net radiation reach the lowest values where SVF is about 0.5. • NUSHMI reaches maximum value when building density is 0.7 and building height is 80 m. • NUSHMI reaches the highest values when building height deviation is about 10 m to 20 m. [ABSTRACT FROM AUTHOR]

Urban greenspace has significant cooling effects on urban heat. Recent studies investigating the effects of spatial configuration of greenspace show significant, but inconsistent results, including both positive and negative effects. To investigate the causes of this inconsistency, we compared Baltimore, MD and Sacramento, CA, USA, two cities with very different climatic conditions. We quantified and compared the relationships between the spatial configuration of trees and land surface temperature (LST) using different statistical approaches, and conducted the analyses using spatial units of different sizes, based on trees mapped from 1 m high resolution imagery. We found: (1) trees' cooling efficiency was higher in Baltimore than in hotter and drier Sacramento. Additionally, percent cover of trees was more important than their spatial configuration in predicting LST in Baltimore, but the opposite was found in Sacramento. (2) Spatial configuration of trees affects LST more in Sacramento than in Baltimore, and the effects of spatial configuration of trees on LST varied greatly in terms of magnitude, significance, and even direction, between the two cities. Notably, mean patch size had significantly positive effects on LST in Baltimore, but negative effects in Sacramento. In contrast, edge density had negative effects on LST in Baltimore, but positive effects in Sacramento. (3) Different statistical approaches resulted in dramatic changes in the relationships between LST and configuration metrics. Our results underscore the necessity of controlling the effects of percent cover of trees, when quantifying the effects of spatial configuration of trees on LST. (4) Spatial autocorrelation may influence relationships between landscape metrics and LST, particularly when the unit of analysis is relatively small. (5) The relationships between spatial configuration metrics and LST are stronger with an increase of the size of the analytical unit. This study can enhance our understanding of the effects of spatial configuration of greenspace on urban heat island (UHI). It also provides important insights to urban planners and natural resource managers on how to mitigate the impact of urbanization on UHI through urban design and vegetation management. [ABSTRACT FROM AUTHOR]

The availability of high spatio-temporal resolution of urban air temperature is paramount for understanding urban heat island (UHI) and developing effective mitigation strategies, in particular for local-scale mitigations. Obtaining high spatial resolution of air temperature at city-scale is challenging as the quantity of weather stations is often limited in cities, particularly in those less developed ones. In this study, based on the existing weather station network in Guangzhou city, China, we compare eight different air temperature predictive models and select one with the best performance to interpolate city-scale air temperature. The training and validation of the models are performed using observatory meteorological data of 321 weather stations in Guangzhou. Deep learning-derived land cover information and social-economic data are encoded to be used as explanatory variables. The regression kriging combined with multiple linear regression is found to result in the best performance, with an average root mean squared error (RMSE) of 0.92 °C and a coefficient of determination (R2) of 0.959. Furthermore, the quantities and locations of current weather stations can be optimized by the proposed model. Guided by the k-means clustering alongside the information of geocoordinates and land cover, the number of current weather stations in Guangzhou can be reduced by 50% (i.e., 160 weather stations) while retaining the model performance. This study proposes and demonstrates an effective model for obtaining city-scale air temperature at high spatio-temporal resolution with data from sparse weather stations, which is much needed for cities which want to enhance their city-scale air temperature mapping by complementing new weather stations to their existing weather station network. • City-scale air temperature map was obtained by machine-learning assisted method. • Eight different air temperature mapping methods were proposed and compared. • Regression kriging using multiple linear regression has the smallest RMSE (0.92 °C). • Land cover data is important for both prediction and monitoring network design. • Weather stations in Guangzhou can be reduced by 50% while retaining performance. [ABSTRACT FROM AUTHOR]

Climate change and the urban heat island effect pose significant health, energy and economic risks. Urban heat mitigation research promotes the use of reflective surfaces to counteract the negative effects of extreme heat. Surface reflectance is a key parameter for understanding, modeling and modifying the urban surface energy balance to cool cities and improve outdoor thermal comfort. The majority of urban surface studies address the impacts of horizontal surface properties at the material and precinct scales. However, there is a gap in research focusing on individual building facades. This paper analyses the results of a novel application of the empirical line method to calibrate a terrestrial low-cost multispectral sensor to recover spectral reflectance from urban vertical surfaces. The high correlation between measured and predicted mean reflectance values per waveband (0.940 (Red) < rs > 0.967 (NIR)) confirmed a near-perfect positive agreement between pairs of samples of ranked scores. The measured and predicted distributions exhibited no statistically significant difference at the 95% confidence level. Accuracy measures indicate absolute errors within previously reported limits and support the utility of a single-target spectral reflectance recovery method for urban heat mitigation studies focusing on individual building facades.