Search Results (243)

The intensifying urban heat island (UHI) effect presents a growing challenge for urban environments, yet there is a lack of comprehensive strategies that account for how multiple factors influence tree-cooling effectiveness throughout the year. While most studies focus on the effects of individual factors, such as tree shading or transpiration, over specific time periods, fewer studies address the combined impact of various factors—such as seasonal variations, building shading, transpiration rates, tree placement, and spacing—on tree cooling across different seasons. This study fills this gap by investigating the thermal environment in downtown Los Angeles through ENVI-met simulations. A novel tree-planting strategy was developed to enhance cooling performance by adjusting tree positions based on these key factors. The results show that the new strategy reduces Universal Thermal Climate Index (UTCI) temperatures by 2.2 °C on the hottest day, 0.97 °C on the coldest day, and 1.52 °C annually. The study also evaluates the negative cooling effects in colder months, demonstrating that, in cities with climates similar to Los Angeles, the benefits of tree cooling in hot weather outweigh the drawbacks during winter. These findings provide a new method for optimizing tree placement in urban planning, contributing to more effective UHI mitigation strategies. Full article

With rapid worldwide urbanization, the urban heat island (UHI) effect is becoming more and more serious. The UHI effect is more intense in industrial areas. Green roofs are an effective way to mitigate UHIs in high-density cities, which calls for thorough examination. This study explored the associations between the block characteristics and block thermal environment in high-density industrial areas based on the widely accepted Local Climate Zone (LCZ) scheme. The pedestrian air temperature comparisons before and after virtual green roof installations presented the cooling effects of green roofs. Thirty-six typical industrial blocks were involved in the study and the simulations were conducted utilizing ENVI-met. The results showed that (1) the air temperature in LCZ4 is significantly lower than those in LCZ2 and LCZ6, but no significant differences were identified between other pairs of LCZ types; (2) the cooling effect of green roofs significantly differs among LCZs, and is associated with sky view factor (SVF), average building area (ABA) and average building shape index (ABSI); (3) in high-density urban areas, additional functional parameters and building-volume indices should be included to better address the physical characteristics, thermal environment, and green roof cooling effect of industrial blocks. This study could improve the validity of LCZ classification for high-density industrial blocks and may provide direct implications for green roof planning. Full article

Road greening markedly impacts road thermal comfort and air quality. However, previous studies have primarily focused on thermal comfort or PM_2.5 individually, with relatively few addressing both aspects comprehensively, particularly in humid regions. This study combined field measurements and simulations. It employed physiological equivalent temperature (PET) and quantified the horizontal distribution of particulate matter 2.5 (PM_2.5). The research examines the effects of planting spacing, tree species, and tree–shrub combinations on pedestrian walkways in humid climates during both summer and winter. Using measured tree data and road PM_2.5, a plant model was established and pollution emission parameters were set to validate the effectiveness of the ENVI-met through fitting simulations under various scenarios. The results indicated that (1) plant spacing for trees influenced both the road thermal environment and PM_2.5 levels. Smaller spacing improved thermal conditions but increased PM_2.5. (2) trees with large canopies and high leaf area indices (LAIs) notably enhanced thermal comfort, while those with smaller canopies and dense understories facilitated PM_2.5 dispersion. The 3 m spacing resulted in a maximum absolute PM_2.5 concentration difference (C) of 5.05 μg/m³ in summer and a maximum mean absolute PM_2.5 concentration difference (M) in the downwind region of 2.13 μg/m³ in winter. (3) Combining trees with shrubs moderately improved pedestrian thermal comfort. However, taller shrubs elevated PM_2.5 concentrations on walkways; heights ranging from 1.5 m to 2 m in summer showed higher C values of 5.38 μg/m³ and 5.37 μg/m³. This study provides references and new perspectives for the optimization of roadway greening design in humid areas in China. Full article

Global warming and urban heat island effects negatively impact the development of urban thermal environments, making them very uncomfortable to live in. Green space plays an essential role in controlling and improving air pollution, regulating the microclimate, and enforcing compliance with public health requirements. Therefore, this study explored the relationship between green space and thermal comfort in the historical neighborhood of Dazhalan in Beijing through questionnaires, observational interviews, and numerical simulations. The current situation of the microclimate environment in the green space of the block was observed first. Then, the microclimate environment was simulated by the ENVI-met 5.6 software. The thermal comfort of the three types of space, such as enclosed space, strip space, and corner space, was also evaluated to explore the coupling relationship between different green space elements and microclimate evaluation factors. It was found that the thermal comfort PET had a positive correlation with the sky openness SVF. The green space morphology was quantitatively measured, and it was found that the thermal comfort PET had a negative correlation with the three-dimensional green quantity of green space. The paper developed managing strategies for optimizing the layout and construction mode of the green space. The ultimate goal was to rationally match the greening planting, improve the pavement of the underlying surface of the block, and optimize the design of the internal space topography. Full article

Considering the impacts of climate change on the goal of obtaining sustainable and healthier cities, this research aimed to analyze and assess the impact of different urban forms with different trees densities on the dynamic physiological equivalent temperature (DPET) for pedestrians while walking further than the average walking distance (750 m) using ENVI-met. This study included five different areas within Greater Cairo, which is suffering from extreme heat stress. The selected study areas had lots of urban variety in terms of the canyons’ aspect ratios, orientations, urban form, green areas, mixed uses, and tree densities. Two tree scenarios were analyzed: the current tree density situation and a scenario where the tree density of each study area was increased to its capacity. The results proved that the DPET had different values than the steady physiological equivalent temperature (SPET) at each point within the walking routes. However, the DPET was closely related to changes in the SPET. Keeping the SPET lower or higher for a long time reduced or increased the DPET, and frequent changes (up and down) in the SPET kept the DPET stable. Changes between DPET values were driven more by the microclimate conditions of a space or canyon than the conditions of the overall area, and controlling the microclimate conditions of a whole urban canyon controlled the DPET. Changes in the DPET could reach as high as 10 °C between different walking routes, and increasing the tree density could help lower the DPET by as much as 6 °C in some cases. Full article

This study investigates the role of vegetation in enhancing thermal comfort and achieving energy savings in educational building courtyards located in hot, arid climates. The research focuses on an educational building courtyard in New Aswan City, Egypt, and employs a combination of field monitoring and numerical simulations to evaluate the thermal performance of the space. The study utilized the ENVI-met V5.5.1 model for thermal assessment and the Design-Builder software version 6.1.3.007 to quantify the potential energy savings. Nine different vegetation scenarios were proposed and analyzed to identify the most effective strategies for improving the courtyard’s thermal conditions. The results demonstrate that a 60% coverage of the courtyard with Cassia Nodosa vegetation produced the most significant improvements. This scenario led to a decrease of over 25.4 °C in physiological equivalent temperature (PET) and a reduction of more than 31.3 °C in mean radiant temperature (T_mrt). Moreover, the energy savings achieved were approximately 19.2%. Interestingly, the study also observed an unexpected decrease in the temperature mitigation efficacy of Ficus nitida when vegetation coverage was increased from 40% to 60%. This phenomenon can be attributed to the complex interplay between the inherent characteristics of the Ficus nitida species and the microclimatic factors within the courtyard environment. These findings provide valuable insights for designers and architects to integrate effective vegetation strategies into the design of educational building courtyards in hot, arid climates. By enhancing thermal comfort and reducing energy consumption, this approach can contribute to the creation of more sustainable and comfortable learning environments. Full article

To investigate the impact of landscape characteristics on microclimate and thermal comfort in summer urban parks in Xinjiang, we focused on Mingzhu Park in Shihezi City. We collected microclimatic data through field measurements and analyzed the correlations among these factors, the physiological equivalent temperature (PET), and the landscape features. ENVI-met was utilized for microclimate simulations to assess the optimization effects. The results revealed that different landscape features significantly influenced the microclimate and thermal comfort. Trees and grass effectively lowered the temperature, increased humidity, reduced wind speeds, blocked solar radiation, and decreased the PET. Water bodies exposed to sunlight and without shade have a low reflectivity, leading to significant temperature increases. While evaporation can lower the surrounding temperatures, the water surface temperature remains higher than in shaded areas, raising temperatures there. The temperature, humidity, wind speed, and mean radiant temperature show significant correlations. The correlation ranking is as follows: mean radiant temperature (T_mrt) > air temperature (T_a) > relative humidity (RH) > wind speed (V_a). After increasing the tree cover and designing dispersed water bodies, the average PET decreased by up to 0.67 °C, with the park experiencing the largest reduction of 1.86 °C. The PET in the eastern built-up area was reduced by 0.35 °C, and in the western built-up area, by only 0.13 °C. Full article

Green space improves outdoor thermal comfort and promotes the residents’ physical and mental health. Currently, many cities are using green volume indicators to evaluate the quality of residential green space and to help form the latest evaluation standards. However, from the perspective of plant green volume, the impact of green space structures on thermal mitigation has not been emphasized. Furthermore, the cost of green space will change with the green space structures. Therefore, we evaluate the impact of changes in green space structures on thermal mitigation and costs from the perspective of plant green volume and aim to find suitable allocations of plant green volume, which balance thermal mitigation with cost savings. This study analyzed the regional climate and residential green space structures. Then, we discussed the relationship between thermal mitigation and the costs of different structures. The analytical results indicated that thermal comfort improves as the green volume of trees increases, with costs also increasing. Where the green volume exceeds 70%, no “extreme heat stress” moments occur for the whole day. When the green volume of trees increases from 20% to 60%, the thermal mitigation is 3.62 °C. However, the mitigation is only 1.74 °C when the green volume increases from 60% to 100%, which is less than half of the former, numerically. This study suggests that the green volume of trees in residential green spaces should be controlled at 60%–70% and the corresponding green volume of shrubs should be 30%–40%. This study rationally balances the thermal mitigation and costs of residential green space, which will directly guide residential green space planning in real situations. Full article

Ongoing global climate change, marked by sustained warming and extreme weather events, poses a severe threat to both the Earth’s ecosystems and human communities. Traditional settlements that underwent natural selection and evolution developed a unique set of features to adapt to and regulate the local climate. A comprehensive exploration of the spatial patterns and mechanisms of the adaptation of these traditional settlements is crucial for investigating low-energy climate adaptation theories and methods as well as enhancing the comfort of future human habitats. This study used numerical simulations and field measurements to investigate the air temperature, relative humidity, wind speed, wind direction, and thermal comfort of traditional settlements in Western Sichuan Plain, China, and uncovered their climate suitability characteristics to determine the impact mechanisms of landscape element configurations (building height, building density, tree coverage, and tree position) and spatial patterns on microclimates within these settlements. The results revealed the structural and layout strategies adopted by traditional settlements to adapt to different climatic conditions, providing valuable insights for future rural protection and planning and enhancing climate resilience through natural means. These findings not only contribute to understanding the climate adaptability of Earth’s ecosystems and traditional settlements but also offer new theories and methods to address the challenges posed by climate change. Full article

The objective of this study is to elucidate the principal determinants influencing the thermal comfort of campus sidewalks, and to discern the nexus between sidewalk planting configurations and thermal comfort. Initially, thermal environment simulations are conducted across various temporal intervals, predicated upon the extant sidewalk planting configuration. Subsequently, an analysis is undertaken to delineate the causative factors contributing to suboptimal thermal comfort within the prevailing milieu. Finally, an evaluation of configurations conducive to enhancing campus thermal comfort through divergent planting design solutions is undertaken, thereby engendering discourse on sidewalk planting design. The findings show that impermeable pavement, encompassing sidewalks and driveways, emerges as the pre-eminent precipitant of diminished thermal comfort within the study locale. The implementation of a double-row staggered tree-planting approach, coupled with multi-layered shrub planting, emerges as the optimal solution for augmenting thermal comfort. Consequently, the outcomes of this study proffer discernibly superior alternatives for ameliorating the heat island effect and fostering the establishment of a sustainable campus paradigm. Full article

This study aims to investigate the characteristics of energy consumption and outdoor thermal comfort within the high-density urban fabric of Changsha. Two different types of building (residential and office), as well as three building forms (point, slab, and enclosed) were analyzed under the local climate zone scheme. Utilizing the ENVI-met 5.6.1 and EnergyPlus 23.2.0 software, simulations were conducted to assess the thermal comfort and energy consumption of 144 architectural models. Then, multiple regression and spatial regression were applied to predict the energy consumption characteristics of the study area. The results showed the following: (1) In the high-density urban area of Changsha, the central business district and historic old town adjacent to the Xiangjiang River are identified as areas with high energy use intensity. (2) Among the residential categories, the point-types LCZ-3 and LCZ-6, as well as the slab-type LCZ-4, exhibit the lowest energy use intensity. In contrast, the enclosed office buildings, LCZ-2 and LCZ-5, are characterized by the highest energy use intensity. (3) Urban form parameters such as floor area ratio and building shape coefficient have a significant impact on EUI_winter, while EUI_summer is highly related to the normalized difference vegetation index and building shape coefficient (BSC). (4) The slab-type LCZ-4 stands out with its notably lower cooling and heating energy use intensity, coupled with excellent thermal comfort, making it particularly well-suited for the climatic conditions of Changsha. Full article

Rapid urbanization and increased human activity have negatively impacted the microclimate of cities, leading to unfavorable conditions for human thermal comfort, particularly in outdoor spaces. Thermal comfort can be improved through various means, such as adjusting the height of urban buildings, the aspect ratio of road widths, and the placement of street trees. This study employed the ENVI-met software V5.5.1 to simulate the microclimate based on aspect ratio (H/W = 1.5) and street tree spacing (6 m) similar to actual conditions with different aspect ratios (H/W = 0.5, 1.0, and 2.0) and street tree spacing (2 m) in Seoul, Republic of Korea. Thermal comfort was assessed through a comprehensive predicted mean vote (PMV) evaluation, considering the gender (male and female) and age (8, 35, and 80 years) of residents in the target area, to determine the optimal urban canyon scenario. The results of the study indicated that the height of the building and the percentage of trees had a significant impact on the temperature and PMV results. When comparing PMV results, women have higher thermal vulnerability than men, and based on age, older adults have higher thermal vulnerability. The aspect ratio of 1.5 and tree spacing of 2 m resulted in the lowest temperature of 35.91 °C at 12:00 p.m. at 0° wind direction and 36.09 °C at 90° wind direction, lower than the actual input value of 36.9 °C. The PMV values were also under the same conditions, with an average PMV by gender of 3.87 at 0° and 4.21 at 90° and an average PMV by age of 3.86 at 0° and 4.19 at 90°. This finding is significant because it can inform the development of planned cities that prioritize urban thermal comfort during summer. This can be achieved through the strategic design of urban canyons and incorporation of street trees in both new and existing cities. Full article

This research highlights that street layouts, including the vegetation ratio, street orientation, and aspect ratio, are key in diminishing urban heat islands (UHIs), building energy use, and carbon emissions. The optimal street layout for minimal building energy consumption, carbon emissions, and maximal outdoor thermal comfort in Tianjin was established via field measurements, ENVI-met 5.6.1, Energy Plus simulations, and correlation analysis. The findings indicate the following: (1) The carbon emissions of winter residential heating energy consumption are 2.9–3.2 times higher than those for summer cooling. Urban design should thus prioritize winter energy efficiency and summer thermal comfort outdoors. (2) The summer street PET (physiological equivalent temperature) inversely correlates with the vegetation ratio and aspect ratio. Winter heating energy use inversely correlates with the street orientation and directly correlates with the aspect ratio. Adequate vegetation and proper orientation can decrease energy and carbon output while enhancing summer outdoor comfort. (3) Streets with an NW–SE orientation, H/W = 0.9, and 50% trees in summer yield the best thermal comfort, while those with an NE–SW orientation, H/W = 0.3, and 50% vegetative trees in winter produce the lowest carbon emissions. These insights are instrumental in refining urban streets and building designs in cold zones. Full article

The urban heat island (UHI) effect is one of the largest climate-related issues concerning our cities due to the localized temperature increase in highly urbanized areas. This paper aims to investigate the impact of UHI mitigation techniques in promoting climate resilience, by reducing urban air temperatures and cooling energy consumption in buildings. To this end, four mitigation solutions regarding the building envelope—green roofs, green walls, cool roofs, and cool walls—were investigated for the city of Bari in Southern Italy and compared with the current baseline scenario. Hence, five scenarios were simulated—using the ENVI-met microclimate software—during three representative summer days, and the resulting microclimate changes were assessed. Based on these analyses, new climate files—one for each scenario—were generated and used as input to run energy simulations in EnergyPlus to estimate the building cooling consumption. Coupling the microclimate and the consumption outcomes, the mitigation strategies were evaluated from both an urban and building point of view. The study shows that urban characteristics, mainly geometry and materials, are crucial for the UHI phenomenon. All the applied technologies seem to be effective. However, green walls proved to be more efficient in reducing outdoor temperatures (1 °C reduction in daily temperatures), while cool walls performed better in reducing cooling energy consumption, with an overall saving of 6% compared to the current scenario. Full article

Green urban squares are essential in densely built neighborhoods and enhance their quality of life. Investment in the greening of urban areas will have a beneficial impact, particularly regarding human thermal comfort. Smaller than parks, squares can be easily spread over the cities and should be part of any neighborhood. While the cooling effect of green squares during hot summer days is increasingly well established, microclimatic assessments during all seasons are still missing. This study aimed to determine whether it is possible to identify an optimal greenery design that maximizes human thermal comfort, as indexed by physiological equivalent temperature (PET), in temperate climates across all seasons. This study employed a “research by design” methodology, utilizing the micrometeorological simulation model ENVI-met to analyze the impact of greenery on PET improvement across different seasons. The objective was to identify the most effective combination of greenery for PET improvement. To achieve these objectives, two urban squares in Munich, Germany were selected. This selection was based on the assumption that typical greening practices, exemplified by the presence of trees, shrubs, and grass, would significantly impact urban squares and their microclimatic effects on human thermal comfort. The small square with a grass surface underneath trees, Alpenplatz, is highly influenced by the surrounding buildings, affecting the sky view factor (SVF), a crucial aspect of the urban environment. Marstallplatz, an open, large square that is not highly affected by urban morphology, was analyzed through simulation scenarios combining grass, shrubs, and trees. The results demonstrate that hot summer days are of primary concern for climate-sensitive urban square design in order to avoid health risks and thus need to be prioritized without compromising comfort for cold days. To attend to both needs, increasing the number of deciduous trees for shading during the day and the amount of grass to enhance air cooling at night are particularly effective. Nevertheless, microclimate design for the spring and autumn periods must also be considered, with the provision of adaptable opportunities for sheltered and sun-exposed spaces. Full article