Urban areas exhibit a distinct heat island effect during the winter.
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Peer-reviewed literature and reference materials confirm that urban areas experience a distinct urban heat island effect during the winter season, with temperatures remaining significantly elevated compared to surrounding rural areas.
The Urban Heat Island (UHI) is a phenomenon that affects many millions of people worldwide. The higher temperatures experienced in urban areas compared to the surrounding countryside has enormous consequences for the health and wellbeing of people living in cities. The increased use of manmade materials and increased anthropogenic heat production are the main causes of the UHI. This has led to the understanding that increased urbanisation is the primary cause of the urban heat island. The UHI effect also leads to increased energy needs that further contribute to the heating of our urban landscape, and the associated environmental and public health consequences. Pavements and roofs dominate the urban surface exposed to solar irradiation. This review article outlines the contribution that pavements make to the UHI effect and analyses localized and citywide mitigation strategies against the UHI. Asphalt Concrete (AC) is one of the most common pavement surfacing materials and is a significant contributor to the UHI. Densely graded AC has low albedo and high volumetric heat capacity, which results in surface temperatures reaching upwards of 60 °C on hot summer days. Cooling the surface of a pavement by utilizing cool pavements has been a consistent theme in recent literature. Cool pavements can be reflective or evaporative. However, the urban geometry and local atmospheric conditions should dictate whether or not these mitigation strategies should be used. Otherwise both of these pavements can actually increase the UHI effect. Increasing the prevalence of green spaces through the installation of street trees, city parks and rooftop gardens has consistently demonstrated a reduction in the UHI effect. Green spaces also increase the cooling effect derived from water and wind sources. This literature review demonstrates that UHI mitigation techniques are best used in combination with each other. As a result of the study, it was concluded that the current mitigation measures need development to make them relevant to various climates and throughout the year. There are also many possible sources of future study, and alternative measures for mitigation have been described, thereby providing scope for future research and development following this review.
Uncontrolled growth in population is the cause of the unplanned, rapid, and unsustainable expansion of urban areas. This has led to a deterioration of environmental conditions for both global and local ecosystems. This research investigates the Urban Heat Island (UHI) phenomenon in Bengaluru and Hyderabad, India, including its spatial and temporal distribution and relation to air pollution. The investigation was conducted in both study locations during the summer and winter seasons, with data spanning from 2001 to 2021. The findings reveal that the maximum UHI intensity in both cities varies seasonally, with the highest values observed during the summer and the lowest during the winter. Annual maximum UHI intensities range from 4.65 °C to 6.69 °C in Bengaluru and from 5.74 °C to 6.82 °C in Hyderabad. The average UHI intensity also exhibits seasonal and annual variations, with the UHI effect being particularly pronounced in Bengaluru. In addition, the study provides the Urban Thermal Field Variance Index (UTFVI), which reveals that both cities consistently face intense UHI impacts throughout the year, greatly affecting the quality of life. Additionally, hotspot analysis reveals an increasing trend in UHI-affected areas over the years in both cities. The study also highlights air pollution concentrations and shows relationships between land surface temperature (LST) and air pollutants, emphasizing the need to alleviate urban heat, enhance air quality, and promote sustainability. This underscores the importance of UHI dynamics in urban environmental management and public health. This study enhances comprehension of UHI dynamics in swiftly urbanizing areas, providing a novel viewpoint on the complex interconnection between urbanization, climate, and air quality. These insights help develop sustainable urban strategies, reducing the negative effects of uncontrolled urbanization and benefiting local communities and the global ecosystem.
Urbanization has increased the surface urban heat island (SUHI) effect. This study uses local climate zones (LCZ) and urban built environment characteristics (UBECs) to explore the factors influencing land surface temperature (LST) and SUHI in various UBECs in Shenyang, China. Google Earth Engine was used to calculate LST. An LCZ map of Shenyang was created to analyze seasonal differences in the SUHI. A correlation model was used to screen the UBEC, and a geographically and temporally weighted regression (GTWR) model was used to explain the spatial variations in the urban heat environment caused by built environments in different seasons. Compared to traditional methods, the GTWR model exhibits better goodness of fit and is more effective in capturing the spatiotemporal heterogeneity of variables. Compact and high-rise areas had higher SUHI effects compared to other LCZs, whereas land-cover LCZs had a cool-island effect. The GTWR model helps planners identify the climatic impacts of each factor in different spatial locations within the study area, as well as variations across seasons. Vegetation-related factors had less impact in densely-built areas, whereas the proportion of blue areas was more effective in alleviating extreme climates in high-density zones. The impact of building density on the heat island effect exhibited substantial spatiotemporal variation, particularly in compact, high-rise LCZs during both seasons. To address extreme winter–summer weather in cold regions, this study examined seasonal SUHIs and their interaction with UBECs, offering strategies and guidance for heat mitigation in urban design.
The phenomenon of Urban Heat Island (UHI) is a result of various factors ranging from increase in urban built-up land to human activities and affected the climate in urban areas. Therefore, the main objectives of the current study are to monitor the temperature variations and assess UHI in Lahore city. In order to measure the UHI, the meteorological data was collected by installing Digital Weather Station WS-1080, at two selected sites, one at Mozang (urban site) and other at Sangra (rural site) from January 15 to 18, 2015 (4 days) in winter season. The results of the study reveal that notable variations of temperature were recorded between Mozang and Sangra. The mean day-time temperature (23.9°C) was higher at Sangra than Mozang (22.8°C). Whereas temperature at night-time was higher at Mozang and lower at Sangra. The R2 value of 0.0041 also demonstrates positive relationship between UHI and dew point at Mozang. The speed and direction of wind also influences the intensity of UHI. During the observational days, the range of UHI was 4.3°C to 6.2°C. Hence, the difference between the minimum and maximum temperature was almost 2°C and it highlighted that the UHI was enhancing. Lastly, few suggestions were proposed to mitigate the issue of UHI.
The process of urbanization has intensified the urban heat environment, with the degradation of thermal conditions closely linked to the morphological characteristics of different functional zones. This study delineated urban functional areas using a multivariate dataset and investigated the seasonal and threshold effects of landscape and architectural features on land surface temperature (LST) through boosted regression tree (BRT) modeling and Spearman correlation analysis. The key findings are as follows: (1) LST exhibits significant seasonal variation, with the strongest urban heat island effect occurring in summer, particularly within industry, business, and public service zones; residence zones experience the greatest temperature fluctuations, with a seasonal difference of 24.71 °C between spring and summer and a peak temperature of 50.18 °C in summer. (2) Fractional vegetation cover (FVC) consistently demonstrates the most pronounced cooling effect across all zones and seasons. Landscape indicators generally dominate the regulation of LST, with their relative contribution exceeding 45% in green land zones. (3) Population density (PD) exerts a significant, seasonally dependent dual effect on LST, where strategic population distribution can effectively mitigate extreme heat events. (4) Mean building height (MBH) plays a vital role in temperature regulation, showing a marked cooling influence particularly in residence and business zones. Both the perimeter-to-area ratio (L
This research investigates the complex interplay between urban heat island (UHI) and urban pollution island in the context of rapid urbanization. Using remote-sensed land surface temperature (LST), the UHI is categorized into five intensity levels. Air pollution monitoring in Arak city, including green spaces, roads, and industrial areas, combines in situ and remote sensing observations for a comprehensive 2019–2020 seasonal analysis. Findings reveal distinct surface UHI patterns, peaking in spring near highly industrialized areas with low greenery and high nitrogen compounds. A significant correlation between LST and pollutant levels is observed in summer in areas with both roads and industrial facilities. Industrial zones consistently exhibit higher LST intensity than green spaces throughout the year. Fall and winter analyses show unique pollution patterns, with sulfur dioxide concentrations peaking near roads in fall due to traffic congestion, and higher nitric oxide and nitrogen dioxide levels in areas with limited green spaces. These observations underscore the intricate relationship between surface UHI and pollutant concentrations, highlighting the multifaceted nature of urban environmental dynamics across diverse seasons and land-use categories.
Urban areas accumulate heat, developing distinct urban climates that differ from the regional climate, leading to elevated mean air temperatures within cities. In tropical climates, such as Bangkok, this urban heat can contribute to high levels of heat stress. This study analyzes the spatial and temporal variation of air temperature in the Bangkok Metropolitan Administration (BMA) using dynamic climate modeling (WRF, v4.2). The analysis focuses on three distinct cli-matic periods: the cool and dry season (November–February), the hot and dry season (March–May), and the wet monsoon season (June–October). Results indicate that during sunrise in the cool and dry season, urban temperatures can be up to 6.4°C higher than those in surrounding rural areas. The highest temperature differences (>4°C) occur at night during this season, with over 50% of BMA’s urban area and population experiencing sustained exposure to these ele-vated temperatures. In contrast, the smallest temperature differences occur in the hot and dry season, despite it being the hottest overall, due to low soil moisture limiting rural cooling. Un-der specific conditions, an urban cool island (Turban < Turban) may develop during the daytime. Compact urban areas exhibit the most significant heating, although vegetated areas within BMA are also affected. These findings support the design of targeted mitigation strategies.
Efforts are being made to make roads safer for cyclists. Sewage tunnel
London's biggest tunnel has just been completed to take sewage from the capital to the East where it is processed.[21]
Climate
London has a temperate oceanic climate (Köppen climate classification: Cfb). It is not usually very hot or cold. It is often cloudy. Summers are generally warm, sometimes hot. Winters are generally cool. Spring and autumn are mild. London has regular, light rain throughout the year. July is the warmest month, with an average temperature at Greenwich of 13.6 °C to 22.8 °C. The coldest month is January, with an average of 2.4 °C to 7.9 °C. The average annual precipitation is fairly low at 583.6 mm, and February is normally the driest month. Drought is sometimes possible, especially during longer heatwaves in summer. Snow is uncommon but usually falls at least once each winter and heavy snow is rarer and does not happen every winter. While snow is uncommon in central London itself, there is more snow in the outer areas; this is because the "urban heat island" the big city generates makes the city about 5 °C warmer than surrounding areas in winter.
Abstract: There is wide consensus amongst climatologists that cities exhibit distinct climates and are typically warmer than their surrounding rural areas. This phenomenon, known as the urban heat island effect, results from unintentional alterations to urban surface properties. These modifications lead to increased absorption of solar radiation, reduced cooling due to slower wind speeds, and lower evapotranspiration rates. Its occurrence presents adverse consequences to the health and comfort of urban built environment occupants, while also increasing energy consumption ensuing from the measures employed to seek relief. These consequences are highlighted as likely to exacerbate further when combined with the existing trend of increasing temperatures from wider climate warming. Adverse heat-related impacts are thus on an upward trend and are gaining wider attention, with the imperative to develop and implement mitigation and adaptation strategies having already gained significant political determination and investment in recent years. Literature has been reviewed here from various knowledge domains, including public health, urban climatology, potamology, limnology, climate change science, and urban planning to provide a concise guide for architects and urban planners to consider when designing and implementing climate-resilient built environments.
The environmental thermal loading on urban buildings is governed by its climate. It has long been recognised that cities exhibit distinct climates, and are typically warmer than surrounding rural areas to describe the influence of the urban heat island (UHI) effect. This distinctiveness must be accounted for when assessing urban energy interactions, with site-specific loading assessments requiring the procurement of data that defines the local microclimate, either from monitoring campaigns, or calculated from governing variables. This paper reviews the stateof- the-art of the latter simulation approaches. An abridged version of this review is also represented by Gunawardena (2021).
In densely built urban environments, microclimate characteristics are critically important in terms of comfort and health conditions for residents (thermal comfort/thermal stress)[1], but also in relation to environmental performance and, implicitly, the energy performance of urban areas. Given the context of climate change, the increasing frequency of heat waves, awareness of the need to ensure conditions for resilience and analysis of variations and developments in the urban microclimate have grown. It is important to note that the evolution of the urban microclimate not only influences the feeling of thermal discomfort experienced by the population in public spaces due to rising outdoor temperatures, but also amplifies the thermal stress resulting from the overheating of indoor spaces [1], including in residential units, resulting in an increase in the energy required for air conditioning. Thus, the simulation of the energy behavior of buildings in urban areas is conditioned by a prior assessment of the UHI intensity in the analyzed area. "Together with climate change, this phenomenon may be crucial to how we view urban areas as living environments."[1]
Against the backdrop of global warming, urban heat island (UHI) are driven by both physical land use change and dynamic functional intensity, yet their independent and interactive effects remain poorly understood. This study deconstructs these dual drivers in Beijing. First, we employed the Logistic-Harmonic model and random forest classifier to conduct fine classification of land use changes, and constructed the Urban Function Intensity Index (IDI) based on nighttime light and NDVI time series, analyzing their individual and combined effects on land surface temperature change (ΔLST). Results reveal distinct spatial patterns: the core area is dominated by intensification, while the suburbs are the primary locus of expansion. The thermal response to IDI is spatially and seasonally heterogeneous, with the suburban areas being most sensitive and winter responses being strongest. In suburban areas, high IDI was +0.27°C higher than low IDI in winter, whereas low IDI was -0.24°C higher than high IDI in summer. Critically, the interaction between IDI and LCintensity reveals unique synergistic warming pathways, such as a ‘low-IDI + high-intensification’ hot spot in the core area driving ΔLST to 0.74°C, and unexpected warming of 0.64°C in suburban areas experiencing ‘medium-low IDI + de-urbanization’ degradation. Collectively, these findings reveal an evolutionary trajectory of thermal environmental responses across the city’s development gradient, providing a new perspective on the "UHI life cycle" in megacities. This study offers a scientific basis for developing targeted, zone-specific thermal regulation strategies.
in the vicinity of large cities, though not all cities have a distinct urban heat island. US Standard Atmosphere University Corporation for Atmospheric
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