Search Results (26)

With urbanization, ozone (O₃) pollution and the urban heat island (UHI) effect have become increasingly prominent. UHI can affect O₃ production and its dilution and dispersion, but the underlying mechanisms remain unclear. This study investigates the spatial and temporal distribution of O₃ pollution and the UHI effect, as well as the influence of UHI on O₃ pollution in the Sichuan Basin. Atmospheric pollution data for O₃ and NO₂ from 2020 were obtained from local environmental monitoring stations, while temperature and single-layer wind field data were sourced from ERA5-Land, a high-resolution atmospheric reanalysis dataset provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). The results indicate the following: (1) O₃ concentrations in the Sichuan Basin exhibit distinct seasonal variations, with the highest levels in spring, followed by summer and autumn, and the lowest in winter. In terms of spatial variation, the overall distribution is highest in western Sichuan, second highest along the Sichuan River, and lowest in central Sichuan. (2) There are significant regional differences in UHII across Sichuan, with medium heat islands (78.63%) dominating western Sichuan, weak heat islands (82.74%) along the Sichuan River, and no heat island (34.79%) or weak heat islands (63.56%) in central Sichuan. Spatially, UHII is mainly distributed in a circular pattern. (3) Typical cities in the Sichuan Basin (Chengdu, Chongqing, Nanchong) show a positive correlation between UHII and O₃ concentration (0.071–0.499), though with an observed temporal lag. This study demonstrates that UHI can influence O₃ concentrations in two ways: first, by altering local heat balance, thereby promoting O₃ production, and second, by generating local winds that contribute to the diffusion or accumulation of O₃, forming distinct O₃ concentration zones. Full article

With the acceleration of urbanization, the urban heat island (UHI) effect has become a major environmental challenge, severely affecting the quality of life of residents and the ecological environment. Quantitative analysis of the factors influencing urban heat island intensity (UHII) is crucial for precise urban planning. Although extensive research has investigated the causes of UHI effects and their spatial variability, most studies focus on macro-scale analyses, overlooking the spatial heterogeneity of thermal characteristics within local climate zones (LCZs) under rapid urbanization. To address this gap, this study took the central urban area of Chengdu, constructing a LCZ map using multisource remote sensing data. Moran’s Index was employed to analyze the spatial clustering effects of UHI across different LCZs. By constructing Ordinary Least Squares (OLS) and Geographically Weighted Regression (GWR) models, the study further explored the influencing factors within these climate zones. The results showed that: (1) Chengdu’s built and natural environments had comparable proportions, with the scattered building zone comprising the highest proportion at 22.12% in the built environment, and the low vegetation zone accounting for 21.8% in the natural environment. The UHII values in this study ranged from 10.2 °C to −1.58 °C, based on specific measurement conditions. Since UHII varied with meteorological conditions, time, seasons, and the selection of rural reference points, these values represented dynamic results during the study period and were not constant. (2) Chengdu’s urban spatial morphology and UHII exhibited significant spatial heterogeneity, with a global Moran’s I index of 0.734, indicating a high degree of spatial correlation. The highest local Moran’s I value was found in the proportion of impervious surfaces (0.776), while the lowest is in the floor area ratio (0.176). (3) The GWR model demonstrated greater explanatory power compared to the OLS model, with a fit of 0.827. The impact of spatial morphological factors on UHII varied significantly across different environments, with the most substantial difference observed in the sky view factor, which has a standard deviation of 13.639. The findings provide precise recommendations for ecological spatial planning, aiming to mitigate the UHI effect and enhance the quality of life for urban residents. Full article

Anthropogenic heat emissions, which are quantified as anthropogenic heat flux (AHF), have attracted significant attention due to their pronounced impacts on urban thermal environments and local climates. However, there remains a notable gap in research regarding the distinctions in the distribution of anthropogenic heat emissions (AHEs) along urban–rural gradients. To address this gap, the present study introduces a new concept—the anthropogenic urban heat island (ArUHI)—where the AHF within urban areas is higher than that in background areas. To quantitatively describe the magnitude and spatial extent of the ArUHI effect, two metrics—namely, ArUHI intensity (ArUHII) and ArUHI footprint (ArUHIFP)—are introduced. We conducted a comprehensive study across 208 cities in China to investigate the spatiotemporal patterns of AHF variations along urban–rural gradients during the period of 2000–2016. In addition, we explored how the complex interactions between land cover and building form components affect changes in the AHF along urban–rural gradients. Additionally, we analyzed how economic zones and city sizes alter the ArUHI intensity and ArUHI footprint. The results showed that 97% (201/208) of Chinese cities exhibited a significant ArUHI effect from 2000 to 2016. The modeled ArUHI intensity value exhibited a substantial increase of nearly fivefold, increasing from 5.55 ± 0.19 W/m² to 26.84 ± 0.99 W/m² over time. Regarding the spatial distribution of the ArUHI footprint, the analysis revealed that, for the majority of cities (86% or 179 out of 208), the ArUHI footprint ranged from 1.5 to 5.5 times that in urban areas. City sizes and economic zones yielded significant influences on the ArUHI intensity and ArUHI footprint values. Building forms were significantly positively correlated with AHF, with R² values higher than 0.94. This study contributes to the understanding of ArUHI effects and their driving factors in China, providing valuable insights for urban climate studies and enhancing our understanding of surface urban heat island mechanisms. Full article

In the context of an increasingly extreme climate, Urban Heat Island (UHI) mitigation of communities through ventilation has recently attracted more attention. To explore the impact mechanisms of different morphological renovation schemes on its wind and thermal environment, this paper selected the Laozheng Community as a case study and: (1) analyzed measured data to quantitatively investigate the UHI within the community; (2) established the CIM-WTEPS system to construct community information models and to conduct wind environment parametric simulation for seven micro-renovation schemes across three levels; (3) performed correlation analyses between morphology indicators and wind environment indicators; (4) conducted the thermal environment parametric simulation of the community under different schemes. The results reveal that: (1) the Laozheng Community exhibits the Urban Heat Island Intensity (UHII) of up to 6 °C; (2) apart from the “ Hollowing “ scheme, which deteriorates the community wind environment, all other schemes optimize it, potentially increasing the average wind speed by up to 0.03m/s and in the renovated area by up to 0.42 m/s; (3) building density is highly correlated with the average wind speed and the proportion of calm wind area, with correlation coefficients of −0.916 (p < 0.01) and 0.894 (p < 0.01), respectively; (4) the adding of shading facilities can enhance the proportion of areas with lower Universal Thermal Climate Index (UTCI) without adversely affecting the optimization effects of the wind environment, achieving an maximum increase of 3.1%. This study provides a reference for optimizing the community’s microclimate through morphological micro-renovations and detailed operations, aiding designers in better controlling community morphology for in future community renewal and design planning, thereby creating a more hospitable outdoor environment. Full article

Urban heat islands (UHIs) aggravate urban heat stress and, therefore, exacerbate heat-related morbidity and mortality as global warming continues. Numerous studies used surface urban heat island intensity (SUHII) to quantify the change in the UHI effect and its drivers for heat mitigation. However, whether the variations in SUHII among cities can demonstrate the physical difference and fluctuation of the urban thermal environment is poorly understood. Here, we present a comparison study on the temporal trends of SUHII and LST in urban and nonurban areas in 13 cities of the Beijing–Tianjin–Hebei (BTH) megaregion in China and further identify different types of changes in SUHII based on the temporal trends of land surface temperature (LST) in urban and nonurban areas from 2000 to 2020. We also measured the effect of the changes in four socioecological factors (i.e., population density, vegetation greenness (EVI), GDP, and built-up area) on the trends of SUHII to understand the dynamic interaction between the UHI effect and socioecological development. We found the following. (1) Nine out of thirteen cities showed a significant increasing trend in SUHII, indicating that the SUHI effects have been intensified in most of the cities in the BTH megaregion. (2) The spatial pattern of summer mean SUHII and LST in urban areas varied greatly. Among the 13 cities, Beijing had the highest mean SUHII, but Handan had the highest urban temperature, which suggests that a city with stronger SUHII does not necessarily have a higher urban temperature or hazardous urban thermal environment. (3) Four types of changes in SUHII were identified in the 13 cities, which resulted from different temporal trends of LST in urban areas and nonurban areas. In particular, one type of increasing trend of SUHII in seven cities resulted from a greater warming trend (increasing LST) in urban than nonurban areas (SUHII↑₁), and another type of increasing trend of SUHII in Beijing and Chengde was attributed to the warming trends (increasing LST) in urban areas and the cooling trends (decreasing LST) in nonurban areas (SUHII↑₂). Meanwhile, the third type of increasing trend of SUHII in Zhangjiakou was due to a greater cooling (decreasing LST) trend in nonurban areas than in urban areas (SUHII↑₃). In contrast, three cities with a decreasing trend of SUHII were caused by the increase in LST in urban and nonurban areas, but the warming trend in nonurban areas was greater than in urban areas (SUHII↓₁). (4) Among the relationship between the trend of SUHII (Trend_SUHII) and the changes in socioecological factors (Trend_{population density}, Trend_{GDP per captica}, Trend_EVI, and Trend_{build-up area}), a significantly positive correlation between Trend_SUHII and Trend_EVI indicated that the change in SUHII was significantly related to an increased rate of EVI. This is mainly because increased vegetation in nonurban areas would result in lower temperatures in nonurban areas. Full article

With the global warming effect and the rapid growth of global urbanization, the concept of urban heat islands (UHIs) has become one of the most important environmental issues in the world. Early studies on UHIs mostly focused on highly developed, large cities and found that urban heat island intensity (UHII) can be as high as 4~7 °C. In recent years, it has also been found that the UHI of medium-sized cities can also reach 4–6 °C. Previous studies have also found that planting, street orientation, and aspect ratio individually have a great impact on the thermal environment of streets, but there are not many studies that comprehensively discuss the synergistic effects of these factors. Therefore, this study takes a tropical, medium-sized city, Chiayi City, as a case study to use the ENVI-met numerical simulation tool to comprehensively compare and analyze the influence of the trees and geometric characteristics of streets on the microclimate and comfort in the streets. As a result, in a tropical, with sea winds (west winds), medium-sized city, by comparison of 12 street schemes with different roadside tree situations (planting or not), orientations (E–W, N–S), and aspect ratios (0.3, 0.7, 1.0), the improvement benefits and possible mechanisms of air temperature, wind speed, MRT, PET, SET, absolute humidity, etc. at the pedestrian street level (H = 1.4 m) were obtained and show that the cooling effect of trees was deeply affected by the street orientation and geometry. An analysis of changes at different heights was also obtained. Finally, design strategy suggestions, such as the street orientation, should be prioritized to be parallel to the prevailing wind; modifying tree shapes or building forms on streets perpendicular to the prevailing wind for creating cool and comfortable streets in future tropical, medium-sized cities were proposed. Full article

The heating and cooling energy consumption levels of urban buildings account for a large and rapidly growing proportion of the total end-use energy consumption of society. The urban heat island (UHI) effect is an important factor influencing the spatiotemporal variations in the heating and cooling energy consumption levels of buildings. However, there is a lack of research on the impact of the UHI on the heating and cooling energy consumption of buildings in cities of different sizes in the Beijing–Tianjin–Hebei urban agglomeration, which is the most urbanized region in northern China. We selected rural reference stations using the remote sensing method, and applied an hourly data set from automatic weather stations, to examine the impact of the UHI on the typical residential building heating and cooling loads in three cities of varied sizes in the Beijing–Tianjin–Hebei urban agglomeration through building energy simulation. The main conclusions were as follows. As the UHI intensity (UHII) increased, the heating load difference between urban and rural areas decreased, while the cooling load difference between urban and rural areas increased in the cities. The average daily heating loads in the urban areas of Beijing, Tianjin, and Shijiazhuang were 8.14, 10.71, and 2.79% lower than those in their rural areas, respectively, while the average daily cooling loads in the urban areas were 6.88, 6.70, and 0.27% higher than those in their rural areas, respectively. Moreover, the absolute hourly load differences between urban and rural areas were significantly larger during the heating periods than during the cooling periods, with the former characterized by being strong at night and weak during the day. During the peak energy load period, the contribution of the UHI to the peak load of residential buildings varied between the cities. During the stable high-load period, from 18:00 to 07:00 the next day in the heating periods (from 18:00 to 05:00 the next day in the cooling periods), the hourly loads in the urban areas of Beijing, Tianjin, and Shijiazhuang were 3.15 (2.48), 3.88 (1.51), and 1.07% (1.09%) lower (higher) than those in their rural areas, respectively. Our analysis highlights the necessity to differentiate the energy supplies for the heating and cooling of urban buildings in different sized cities in the region. Full article

Urban morphology quantitatively expresses a city’s spatial structure, internal relationships, and physical form. It has advantages for predicting urban growth and analyzing the current state of cities in the literature. A comprehensive study on the complex relationships between urban morphology and urban heat island intensity (UHII) is of great importance for mitigating the urban heat island (UHI) effect for megacities. This study models urban morphological indicators in fine resolution based on three aspects: building morphology, ecological infrastructure, and human activities. The model accurately captures UHII by employing the definition of UHI effects. The relationship between urban morphology and UHII was further examined using extreme gradient boosting (XGBoost) and Shapley additive explanations (SHAP). By taking central Beijing, China as study area, major findings include the following: (1) Significant daytime UHI effects were observed within the research area, particularly during the summer months, when it appears to be most severe. More than 90% of the region experiences varying degrees of the UHI effects. (2) UHI is significantly correlated with both 2D and 3D urban morphological indicators. Low sky view factor (SVF) and high SVF tend to mitigate UHI, whereas moderate SVF tends to aggravate UHI. (3) In densely populated areas, tall trees may be more effective than other forms of vegetation at mitigating UHI. Based on the aforementioned findings, this article suggests that urban morphology optimization should focus on seasonality, spatial specificity, and indicator specificity for megacities in urban design and spatial planning aimed at mitigating UHI. Full article

In this study, we investigated the association between weather type (WT) and urban heat island intensity (UHII) in the region of Attica (Greece). The application of the methodology resulted in ten WTs over the Attica region. The UHII was calculated for every hour of the day from 2008 to 2017, using a new air temperature dataset produced by Copernicus Climate Change Service. To obtain more definitive findings about the relationship between WTs and UHII, we also used the upper 5% of UHII (urban overheating, UO). UO was estimated for two time intervals (daytime and nighttime) and for the warm period (June–September). The UHII frequency distribution, as well as the spatiotemporal characteristics of the UO, were also investigated. It was found that UO was amplified under WT2 during the night, while WT10 was mainly related to increased UO magnitudes in the daytime in all months. Furthermore, analysis results revealed that the UO effect is more pronounced in Athens during the night, especially at the Athens center. The daytime hot spots identified were mainly in suburban and rural areas. Therefore, this methodology may help with heat mitigation strategies and climate adaptation measures in urban environments. Full article

Rapid urbanization has led to drastic land-use/cover changes (LUCCs) and urban heat islands (UHIs), negatively altering the urban climate and air quality. LUCC’s significant impacts on human health and energy consumption have inspired researchers to develop nature-based solutions to mitigate UHIs and improve air quality. However, integrating GIS-CFD modeling for urban heat mitigation towards climate change adaptation was largely neglected for eco-sustainable urban design in rapidly urbanizing areas. In this study, (1) long-term LUCC and meteorological analysis were conducted in the Wuhan metropolitan area from 1980 to 2016; (2) to mitigate the adverse effects of LUCC under a speedy development process, the role and relevance of optimizing building morphology and urban block configuration were discussed; (3) and particular design attention in strategy towards climate change adaptation for environmental performance improvement was paid in Wuhan’s fast-growing zones. The results show that UHII in 1980 was less severe than in 2016. Air temperature (Ta) increased by 0.4 °C on average per decade in developing areas. This increases the severity of UHII in urban fringes. It is found obligatory for a nature-based design to adopt urban morphology indicators (UMIs) such as average building height (μBH), sky view factors (ψ_SVF), and building density (BD/λ_p = % of built area) towards these changes. Further, on-site measurement revealed that λ_p is the most effective indicator for increasing urban heat around the buildings and boosting UHII. Using UMIs and a combined three-in-one regulation strategy based on μBH of common building types of high-rise (BH^A), mid-rise (BH^B), and low-rise (BH^C) buildings can effectively contribute to regulating Ta and air movement within block configuration. As a result of this study’s strategy, urban heat is mitigated via reinforcing wind in order to adapt to climate change, which impacts the quality of life directly in developing areas. Full article

The rapid growth of urbanization significantly influences local atmospheric conditions and life quality of residents living in urban areas by creating a localized phenomenon known as an urban heat island. Urban heat island characteristics are strongly formed by prevailing atmospheric conditions influencing their magnitude and intensity. In this study, we used the Weather Research and Forecasting model to investigate the effects of different airmass and windspeed characteristics on the diurnal cycle of the urban heat island phenomenon during four real weather situations presenting typical scenarios with clear sky conditions. The scenarios consisted of warm dynamic and non-dynamic situations and cold dynamic and non-dynamic situations identified with respect to temperature profiles, humidity and wind speed. The comparison of urban heat island intensity between all four scenarios showed a significant effect of wind speed on urban heat island characteristics and intensity as well as the role of humidity and airmass temperature in diurnal changes. The results showed that urban heat island is best defined by conditions with strong radiative heating and weak wind speed regardless of temperature. Air humidity appears to have significant influence on UHII with cold non-dynamic situations in dry air showing a very high UHII amplitude during the daylight period and high intensity during the night. The comparison of warm and cold dynamics situations showed the influence of vertical heat exchange with strong mixing of air between near-surface levels and lower levels of the troposphere with a mild effect on UHII during the warm situation and strong influence on decreasing UHII during the cold scenario. Full article

This study used homogenised mean, maximum, and minimum daily temperatures from 12 stations located in Brno, Czechia, during the 2011–2020 period to analyse heat waves (HW) and their impact on the canopy urban heat island (UHI). HWs were recognized as at least three consecutive days with T_x ≥ 30 °C and urban–rural and intra-urban differences in their measures were analysed. To express the HWs contribution to UHI, we calculated the UHI intensities (UHII) separately during and outside of HWs to determine the heat magnitude (HM). Our results show that all HW measures are significantly higher in urban areas. UHII is mostly positive, on average 0.65 °C; however, day-time UHII is clearly greater (1.93 °C). Furthermore, day-time UHII is amplified during HWs, since HM is on average almost 0.5 °C and in LCZ 2 it is even 0.9 °C. Land use parameters correlate well with UHII and HM at night, but not during the day, indicating that other factors can affect the air temperature extremity. Considering a long-term context, the air temperature extremity has been significantly increasing recently in the region, together with a higher frequency of circulation types that favour the occurrence of HWs, and the last decade mainly contributed to this increase. Full article

The presence of higher air temperatures in the city in comparison with the surrounding rural areas is an alarming phenomenon named the urban heat island (UHI). In the last decade, the scientific community demonstrated the severity of the phenomenon amplified by the combination of heat waves. In southern Italy, the UHI is becoming increasingly serious due to the presence of a warming climate, extensive urbanization and an aging population. In order to extensively investigate such phenomenon in several cities, recent research calibrated quantitative indexes to forecast the maximum UHI intensity in urban districts by exploiting multicriteria approaches and open-source data. This paper proposes different mitigation strategy to mitigate the Urban Heat Island Intensity in Bari. Firstly, the research evaluates the absolute max UHI intensity of the 17 urban districts of Bari (a city in southern Italy, Puglia) by exploiting the recent index-based approach $I_{UHII}$. Secondly, a comparative evaluation of seven European cities (Bari, Alicante, Madrid, Paris, Berlin, Milan and London) is achieved to point out the positives and negative aspects of the different urban districts. In total, the comparison required the analysis of 344 districts of 7 European cities: 17 districts in Bari (Italia); 9 districts in Alicante (Spain); 21 in Madrid (Spain); 80 in Paris (France); 96 in Berlin (Germany); 88 in Milan (Italy) and 33 in London (UK). Finally, the results emphasize some virtuous examples of UHII mitigation in the major European cities useful to draw inspiration for effective mitigation strategies suitable for the urban context of Bari. Full article

Extreme heat wave weather phenomena have erupted worldwide in recent years. The urban heat island (UHI) effect has exacerbated urban heat waves with serious consequences for urban energy and residents’ health. Therefore, a better understanding of the dynamics of the UHI effect and the influencing factors is needed in the context of carbon neutrality and global warming. This study used long-term observation and statistical data to investigate the urban heat island intensity (UHII) over the past 39 years (1981–2019) and to analyze the temporal changes of the UHI effect and the relationship between the UHI effect and indicators of rapid urbanization in Zhengzhou, China. The results showed that Zhengzhou is warming 2.2-times faster than the global land warming trend of about +0.9 °C from 1981 to 2019. There is a clear phase characteristic of the heat island effect in Zhengzhou, and it offers a rapid upward trend after 2000 and a positive correlation with the urbanization process; it was found that the social and economic conditions of urban expansion in Zhengzhou have a significant relationship with UHII. We also found that the denser the urban built-up area, the more obvious the heat island effect. Compared with other countries, the influence of national policies on urban development is an indirect factor influencing the change of UHI specifically for Chinese cities. This research could provide a reference for understanding the temporal dynamics of UHI in an expanding large city for sustainable urban planning and mitigating urban warming and environmental problems. Full article

Urban development always has a strong impact on the urban thermal environment, but it is unclear to what extent urbanization factors influence urban heat island intensity (UHII) in mountainous cities, and fewer studies have been conducted on the trends of long-term UHII in mountainous cities. Chongqing, as the only municipality directly under the central government in Southwest China and a typical mountainous city, is chosen as the case study. This study analyzed the interannual and seasonal variations of UHII based on the data from meteorological stations in Chongqing from 1959 to 2018 using the least-squares method and the Mann–Kendall test, and explored the relationship between urbanization factors (urban resident population, gross domestic product (GDP), fixed investments, and gross industrial output value) and UHII. The results show that the increasing rates of temperature in urban areas of Chongqing are significantly higher than those in rural areas affected by urbanization. Using the Mann–Kendall test, it is found that almost all abrupt temperature changes in Chongqing occurred after the rapid urbanization of Chongqing in the 21st century. The annual mean UHII increased from 0.1 °C to 1.5 °C during the study period, with summer making the largest contribution. It is also found that the UHII in Chongqing has increased year by year, especially after the 1980s. The increasing rates of UHII are larger at night and smaller during the day. The increasing trends of nighttime UHII are statistically significant, while those of daytime UHII are not. In addition, UHII and urbanization factors are found to be correlated using the grey relational analysis (GRA). Eventually, a comprehensive UHII index and a comprehensive urbanization index are constructed using principal component analysis (PCA). A tertiary regression model of UHII and urbanization index is established, which reflects that the UHII in Chongqing will continue to grow rapidly with the development of the city. Full article