Radiative Cooling Benefits of Materials Applied to the Steel Furnace Slag Use in Asphalt Pavement in a City

Mesoscale meteorological modeling was conducted to evaluate air temperature at 2‐m above surface (T2), wind speed/direction, and relative humidity (RH) in Singapore, a tropical city, for a dry period. A sensitivity study was conducted to determine the best combination of schemes for the physical modules. The model was used to study the urban heat island (UHI) effect and urban cooling effect by applying cool coating on various urban surfaces. Maximum UHI intensity of 3.2°C is found at nighttime (21:00) at a hot spot in the Commercial/Industrial area. At nighttime, when the UHI effect is generally more intense than daytime, applying cool coating on all urban surfaces can reduce the UHI effect by about 30% in residential areas and about 6% in commercial/industrial areas. Maximum T2 reduction of 3.1°C and surface skin temperature (TSK) reduction of 9.8°C due to cool coating is found at 13:00 at certain locations. The cool urban surfaces reduce radiative heat absorption during daytime, reducing heat storage in urban structures. This leads to subsequent reduction of stored heat release from urban structures, mitigating UHI effect during nighttime. Applying cool coating on horizontal surfaces (roofs and roads) provides more cooling effect than vertical surfaces (walls). Cool roofs provide more cooling effect than cool roads since roofs cover more urban horizontal surfaces than roads do in the current setting. Part of the radiation reflected by cool roads could be absorbed by other urban structures, reducing its cooling effect as compared to cool roofs.

The urban heat island (UHI) effect increases the ambient temperatures in cities and alters the energy budget of building materials. Urban surfaces such as pavements and roofs absorb solar heat and re-emit it back into the atmosphere, contributing towards the UHI effect. Over the past few decades, researchers have identified albedo and thermal inertia as two of the most significant thermal properties that influence pavement surface temperatures under a given solar load. However, published data for comparisons of albedo and thermal inertia are currently inadequate. This work focuses on asphalt and concrete as two important materials used in the construction of pavements. Computational fluid dynamics (CFD) analyses are performed on asphalt and concrete pavements with the same dimensions and under the same ambient conditions. Under given conditions, the pavement top surface temperature is evaluated with varying albedo and thermal inertia values. The results show that the asphalt surface temperatures are consistently higher than the concrete surface temperatures. Surface temperatures under solar load reduce with increasing albedo and thermal inertia values for both asphalt and concrete pavements. The CFD results show that increasing the albedo is more effective in reducing pavement surface temperatures than increasing the thermal inertia.

This paper focuses on the monitoring of the urban heat island (UHI) effect with temporal and spatial variation, combining Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Thematic Mapper (TM) data. Our study area is located in the central urban area of Beijing, which mainly refers to the areas within the fifth ring road. For detecting UHI changes over the years 2002–2006, three ASTER images in the summers of 2003, 2004 and 2006 and two TM datasets in the summers of 2002 and 2005 were collected. For monitoring UHI changes with the seasons, three ASTER images and one TM image in 2004 in winter, spring, summer and autumn, respectively, were employed. To calculate the urban heat island intensity, the land surface temperatures were retrieved iteratively for ASTER data and using a generalized single-channel method for the TM image. Four separated regions located in four directions outside the fifth ring road were selected as representing rural comparative regions. Their averaged land surface temperature was regarded as the rural comparative temperature. The UHI intensity was computed by the difference between the pixel urban land surface temperature in the urban area and the comparative temperature in the rural area. Detection of the UHI effect over 2002 to 2006 indicated that most of the areas with high UHI effect were the industrial land use regions and the areas having a high density of buildings, roads, transportations and residents; and the areas without UHI effect were located around the regions with large areas of grassland, trees and water bodies. Our results also showed that the UHI effect was not proportional to urbanization over time. Statistical UHI data during 20 July to 20 September in 2003–2008 also support this point. The monitoring of the UHI effect over seasons (winter, spring, summer and autumn) showed that the urban area of Beijing city had a high UHI effect except in winter, when the urban area of Beijing was in an urban heat sink; the UHI effect increased in spring, summer and autumn.

Exploring the spatial heterogeneity of urban heat island effect and its relationship to block morphology with the geographically weighted regression model

Urban heat island effect: A systematic review of spatio-temporal factors, data, methods, and mitigation measures

The interaction of an urban heat island with a sea breeze front during moist convection over <scp>Tianjin, China</scp>

Author index for volume 233

Green buildings are an important constituent part of the urban ecosystem; they act as an adjuster of temperature and humidity of the environment in cities, and can effectively alleviate the Urban Heat Island (UHI) effect. Existing studies on the UHI effect generally ignored the local information in the changes of the UHI effect, and the impact of the optimization of green building distribution on the UHI effect hadn’t been taken into consideration. To fill in this research gap, this paper aims to study the optimization of the distribution of green buildings based on the UHI effect. At first, this paper adopted a high-precision radiative transfer model to invert the temperature of earth surface in cities, and accurately calculate the UHI effect. Then, this paper analyzed the changes in the UHI effect caused by the optimization of the distribution of green buildings and the response of human activities, and used the time variation law of the single pixels of green buildings to reflect the spatial variation law of the UHI effect. At last, experimental results gave the optimization results of the distribution of green buildings based on the UHI effect.

Abstract. Along with urbanization, sealing of vegetated land and evaporation surfaces by impermeable materials, lead to changes in urban climate. This phenomenon is observed as temperatures several degrees higher in densely urbanized areas compared to the rural land at the urban fringe particularly at nights, so-called Urban Heat Island. Urban Heat Island (UHI) effect is related with urban form, pattern and building materials so far as it is associated with meteorological conditions, air pollution, excess heat from cooling. UHI effect has negative influences on human health, as well as other environmental problems such as higher energy demand, air pollution, and water shortage. Urban Heat Island (UHI) effect has long been studied by observations of air temperature from thermometers. However, with the advent and proliferation of remote sensing technology, synoptic coverage and better representations of spatial variation of surface temperature became possible. This has opened new avenues for the observation capabilities and research of UHIs. In this study, "UHI effect and its relation to factors that cause it" is explored for İzmit city which has been subject to excess urbanization and industrialization during the past decades. Spatial distribution and variation of UHI effect in İzmit is analysed using Landsat 8 and ASTER day &amp;amp; night images of 2015 summer. Surface temperature data derived from thermal bands of the images were analysed for UHI effect. Higher temperatures were classified into 4 grades of UHIs and mapped both for day and night. Inadequate urban form, pattern, density, high buildings and paved surfaces at the expanse of soil ground and vegetation cover are the main factors that cause microclimates giving rise to spatial variations in temperatures across cities. These factors quantified as land surface/cover parameters for the study include vegetation index (NDVI), imperviousness (NDISI), albedo, solar insolation, Sky View Factor (SVF), building envelope, distance to sea, and traffic space density. These parameters that cause variation in intra-city temperatures were evaluated for their relationship with different grades of UHIs. Zonal statistics of UHI classes and variations in average value of parameters were interpreted. The outcomes that highlight local temperature peaks are proposed to the attention of the decision makers for mitigation of Urban Heat Island effect in the city at local and neighbourhood scale.

An afternoon heavy rainfall event occurred over coastal Nantong, an area of 70–100 km downstream from the Shanghai–Suzhou–Wuxi–Changzhou city belt over the Yangtze River Delta, under the influences of weak southwesterly monsoonal flows and lake/sea breezes on 26 July 2018. An observational analysis shows the emergence of pronounced urban heat island (UHI) effects along the city belt during the late morning hours. A series of nested-grid cloud-permitting model simulations with the finest grid spacing of 1 km are performed to examine the impacts of urbanization on convection initiation (CI) and the subsequent heavy rainfall event. Results reveal the generation of lake breezes and warm anomalies in the planetary boundary layer along the city belt and low-level convergence, thereby inducing upward motion for CI. The southwesterly flows of the monsoonal warm–moist air, enhanced by the UHI effects along the city belt, allow the development of convective cells along the city belt, some of which merge with convective clusters during their downstream propagation, and the ultimate generation of several distinct heavy rainfall centers by local convective clusters over coastal Nantong where atmospheric columns are more moist and potentially unstable under the influences of sea breezes. Sensitivity simulations show small contribution of Nantong’s UHI effects to the heavy rainfall event. The above findings help elucidate how the UHI effects could assist the CI in a weak-gradient environment, and explain why urbanization can contribute to increased downwind mean and extreme precipitation under the influences of favorable regional forcing conditions. Significance Statement The urban heat island (UHI) effects tend to produce more rainfall on its downwind side than that on the other sides, but alone could hardly account for the generation of heavy rainfall. This study examines the influences of the UHI effects associated with a city belt over the Yangtze River Delta on generating an afternoon heavy rainfall event over coastal Nantong that is 70–100 km downwind from the city belt. Results show (i) the downwind advection of the UHI effects; (ii) the initiation of convective storms along the city belt, and their subsequent downstream propagation, leading to the generation of heavy rainfall over Nantong; and (iii) an important role of sea breezes in generating the heavy rainfall event.

Impacts of urbanisation on the thermal behaviour of new built up environments: A scoping study of the urban heat island in Bahrain

In Ukraine a significant part of motor roads with flexible pavement, especially local ones, serves with cracks in asphalt concrete layers during long period. Asphalt concrete spalling in the zone of open crack edges is a further stage of pavement layer deterioration during its long period of service. Costs for repair of these defects are much higher than for crack sealing. Monitoring of actual condition of flexible pavements in various regions of Ukraine indicates that cracks in asphalt concrete pavement appear in different locations, have different direction and pattern, width, depth and length. Number of cracks, their frequency of location on the pavement, length and width of opening at low temperatures depend on duration of the pavement exploitation. Today there are no exact regulations on structural and technological decisions in terms of crack preparation and sealing with regard to their width and activity in normative and technical documents. The topic of the paper is development of structural and technological decisions for crack preparation and sealing in asphalt concrete pavements with regard to their width and activity. It is noted that hot-applied bituminous sealing materials are the most popular in Ukraine for works on crack sealing in asphalt concrete road pavements. Based on the results of scientific and technical supervision of various crack sealing techniques in asphalt concrete road pavements it is shown that crack sealing can be performed with preliminary routing (rectangular rout) in zone of crack or without routing. It is noted that cracks with preliminary routing can be sealed with overband or without overband of sealing material on the surface of asphalt pavement. Technique of crack sealing by filling of the created rout with bitumen-polymer mastic or hot-applied sealant with overband on asphalt pavement surface provides the highest watertightness and durability of the sealed crack, in comparison with sealing by filling of the created rout flush with asphalt pavement, or without routing. Classification of cracks in asphalt concrete pavements is proposed and structural and technological decisions on crack preparation and sealing are described.

Investigating the urban heat island effect of transit oriented development in Brisbane

In order to reduce asphalt pavements temperature and mitigate the urban heat island (UHI) effect, a solar heat reflective coating (HRC) was introduced and applied to the surface of asphalt pavement. Main purpose of this paper is to evaluate the temperature reduction and UHI effect of HRC on asphalt pavement. On the basis of the principles of heat reflection, the HRC was synthesized. The antiskid performance and water permeability of the concretes covered with and without HRC were monitored and compared. Meanwhile, an accelerated loading test with loaded vehicles was performed for these two asphalt concretes. The influence of the reduction in the surface temperature on the air temperature was simulated. The research results indicate that the HRC features a good waterproof ability, as well as it can obviously reduce the surface temperature of asphalt concrete for its high light-reflection rate. Furthermore, the accelerated loading test also suggests that the HRC improves the rutting resistance of the asphalt concrete when exposed to the same irradiation strength. Friction coefficient had slightly reduction, and hence the skid-resistant granular should be recommended to added in asphalt pavement. Therefore, this HRC on asphalt pavement could be adopted as a countermeasure against the UHI effect.

Pavements are one of the major contributors to the urban heat island (UHI) effect of cities because they cover a considerably large fraction of urban ground surfaces. Permeable pavements are considered an effective solution for mitigating the heat island effect in hot climates. In this study, the effect of pavement types on mitigating the UHI was investigated through a series of laboratory simulation experiments. Three commonly used pavement materials, asphalt concrete (AC), traditional Portland cement concrete (PCC), and Portland cement porous concrete (PCPC), were considered for the study. The thermal performances of those materials under simulated conditions were examined with specially designed testing methods. The testing results showed that under the same thermal radiation conditions, the surface temperature of PCPC was equivalent to that of PCC, whereas the AC showed much higher surface temperature. This indicates that AC pavements usually absorb more heats than PCC and PCPC pavements under solar radiations. Compared to the PCC, the AC and PCPC usually reflected less heat to the surrounding environments due to their relatively lower albedo values, which could mitigate the thermal discomfort for the nearby human and buildings to some extent. In addition, the PCC could store more thermal energy in day time and release them back to the atmosphere at night due to its relatively high density, thermal conductance and specific heat capacity. This indicates that PCC could produce negatively effects on the UHI at night.