Impact of rapid urbanization on urban heat island effect in a typical valley-city

Assessing spatiotemporal characteristics of urban heat islands from the perspective of an urban expansion and green infrastructure

Rapid urbanization has aggravated the urban thermal risk and highlighted the urban heat island (UHI) effect. To improve understanding on the effect of urbanization on the UHI effect, it is essential to determine the relationship between the UHI effect and the complexities of urban function and landscape structure. For this purpose, 5116 urban function zones (UFZs), representing the basic function units of urban planning, were identified in Beijing. Land cover and land surface temperature (LST) values were extracted based on remote sensing data. UFZ, land cover, and LST were used to represent the urban function, landscape, and UHI characteristics, respectively. Then, the effects of urban function and landscape structure on the UHI effect were examined. The results indicated that the urban thermal environment exhibited obvious spatiotemporal heterogeneity due to the variation of urban function and landscape complexity: (1) UFZs showed significantly different LST characteristics for different functions and seasons, and the mean LST gap among different types of UFZ can reach 1.72–3.85 °C. (2) During warm seasons, the UHI region is mainly composed of residential, industrial, and commercial zones, while recreational zones contribute as an important UHI source region during cold seasons. (3) Urban developed land and forest are the most important landscape factors contributing to the UFZ effect in the urban thermal environment. These findings have useful implications for urban landscape zoning to mitigate the UHI effect.

Assessing the urban heat island effect of different local climate zones in Guangzhou, China

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

Human health, energy and comfort are determined by the climate that remains in the physical environment. Regarding urban climate, few studies assess the urban heat island effect, heat stress, and public health as geographical representations. This study seeks to fill this gap by selecting Colombo, Sri Lanka, and Shenzhen, China, comparatively, two coastal cities with different climate conditions. We quantified and compared the effects of heat waves and their impacts on public health and the effect of urbanization on urban heat islands (UHI). Heat-related public health issues have been calculated using the Wet-Bulb Globe Temperature (WBGT) index. The Urban Heat Island (UHI) effect was analyzed using Land Surface Temperature (LST), created based on Landsat images obtained in 1997, 2009 and 2019. A rapid increase in temperature and humidity creates an uncomfortable environment in both cities, but apparent differences can be observed in climatic phenomena. During the summer (June to August), the prevailing atmospheric condition in Shenzhen makes a “Very severe stress” with Heatstroke highly likely. Nevertheless, seven months (November to April) are found as “Comfortable” without having any heat-related health injuries. However, Colombo has never been classified as “Comfortable” throughout the year. Out of twelve, five months (April to August) are found as “Very severe stress” with Heatstroke highly likely. When considering the urban expansion and UHI, a fast expansion can be observed in Colombo than in Shenzhen. Consequently, with the more severe heat-related public health and rapid urban heat island expansion, Colombo makes it more stressful than Shenzhen city. Our findings highlight the comparison between heat-related public health and urban heat island between two coastal cities with different climate conditions and under rapid urbanization processes. Therefore, it is imperative to assess these risks and respond effectively.

Author index for volume 233

Urban heat island effect of a typical valley city in China: Responds to the global warming and rapid urbanization

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 & 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.

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.

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.

The middle and lower reaches of the Yangtze River are frequently affected by the Western Pacific Subtropical High (WPSH) in summer. This leads to phenomena including air subsidence, high temperatures, low rainfall, and weak winds, all of which affect the urban heat island (UHI) effect. Currently, there are few studies on the influence of WPSH on the UHI effect. In this study, we analysed the temporal and spatial distributions of the influence of WPSH on the UHI effect by establishing two scenarios: with and without WPSH. We calculated the UHI intensity and the urban heat island proportion index (UHPI) to analyse the temporal and spatial distributions of the UHI effect. The geographical detector method was then used to analyse the factors influencing UHI. The results indicate the strong heat island effect during the day in provincial capitals and some developed cities. The area of high UHI intensity was larger under the influence of WPSH than in the years without WPSH. WPSH affected UHPI at both day and night, although the effect was more pronounced at night. The factors affecting daytime UHI intensity are mainly POP and NTL, O3 plays a large role in the years with WPSH control. The main factors affecting the UHI intensity at night are AOD, POP and NTL were mainly factors in the years without WPSH control, POP and WPSH were mainly factors in the years with WPSH control. The interactions of the factors are mainly POP and multi-factors during the daytime, and DEM and multi-factors during the nighttime. It was found that the UHI intensity was enhanced under the control of the WPSH, and the influencing factors of the diurnal UHI differed with and without the WPSH control, which ultimately provides realistic suggestions for mitigating the intensity of the UHI in areas affected by the WPSH.

The Urban Heat Island (UHI) effect, characterized by elevated urban temperatures compared to rural areas, is a critical challenge in urban climatology, exacerbated by global warming and rapid urbanization. This study investigates the fundamental mechanisms of the UHI effect by integrating theoretical modeling with observational data from Korea, focusing on the interplay between urban heat storage, anthropogenic heat, and climatic factors. Using a simplified day-night model based on the Surface Energy Flux Balance (SEFB) framework, we demonstrate that the UHI effect arises primarily from two mechanisms: (1) a decrease in the diurnal temperature range (DTR) due to the increased heat capacity of urban materials, and (2) an increase in mean temperature driven by additional energy fluxes, such as anthropogenic heat. Comparative analysis between Seoul, a major city, and Boeun, a rural area, reveals qualitative agreement between model predictions and observed data. Despite its higher latitude, Seoul exhibits significantly higher nighttime temperatures than Boeun, underscoring the role of urban heat storage in sustaining nighttime warming. Additionally, a temporary daytime temperature inversion in Boeun, driven by greater solar radiation, highlights the contrasting thermal dynamics between urban and rural environments. Long-term analyses reveal distinct evolutionary patterns of UHI effects in major cities and new towns. In major cities, rapid urbanization from the 1970s to the 1990s led to a steady decrease in DTR and a peak in nighttime temperature differences, followed by stabilization. In contrast, new towns consistently increased nighttime temperature differences, closely tied to urban development and population growth. Both cases demonstrate the critical role of heat storage and anthropogenic heat in shaping the UHI effect, with observed trends closely mirroring theoretical predictions. This study emphasizes the vulnerability of urban areas to climate change, as UHI effects amplify global warming's impact, heightening urban heat stress.

Urban and suburban areas experience elevated temperatures compared to their surrounding rural areas. This is well known as the urban heat island (UHI) effect, which is a common and an important effect of urbanization. The UHI effect is well known for the large cities around the world, and most of the recent studies were conducted there. UHI effects are less intense or less frequent in smaller urban areas compared to larger urban areas. However, this is not well understood since there is a significant lack of UHI effect studies on smaller cities. The city of Chattanooga, TN, is one of the fastest-growing cities in Tennessee. As urbanization continues in the greater Chattanooga area, it is very important to understand the possible UHI effect on sustainable development efforts in this area. Remote sensing technology has been used successfully to study the UHI effect for many large cities in the United States and the rest of the world. Using thermal images acquired by NASA’s Landsat‐8 satellite during the summers of 2018 and 2019, a recent study conducted in the Geological and Environmental Remote Sensing Laboratory at the University of Tennessee at Chattanooga found that the city of Chattanooga behaves like an UHI, and its effect is significant. Recently, we installed eight temperature-measuring stations across the city of Chattanooga, TN, to acquire air temperature at a 2‐m height from the ground. We have been acquiring temperature data every 10 min since March 2023. This study incorporated ground measured air temperature with the ongoing remote sensing-based study to better understand the UHI effect. The obtained results confirmed that the city of Chattanooga, TN, indeed behaves like an UHI. Both satellite-derived land surface temperature and direct air temperature measurements clearly captured the UHI effect, and their UHI profiles were comparable, with root mean square error values ranging from 5.0 to 7.5°F for different dates and 2.2 to 7.7°F for each station. While thermal images are particularly useful for mapping the spatial variation of UHI effects, air temperature measurements provide the advantage of capturing temporal variations throughout the day.

Rapid urbanization has resulted in urban heat island (UHI) effects becoming a global environmental issue. Urban green space (UGS) can effectively alleviate UHI effects; however, how their spatial arrangements and the cooling radiation region effects on UGS are relatively poorly understood. To advance our understanding, we analyzed Landsat imagery from 2010 to 2021 for the world’s first fine classification product of surface cover to quantitatively analyze the cooling radiation range of UGS. We used buffer analysis to measure the impact of the spatial distribution of UGS on UHI effects from normalized difference vegetation index (NDVI) and variance mean ratio (VMR). UGS has its greatest cooling effect in summer, among which evergreen coniferous forests contribute the most to cooling and grasslands contribute the least. The cooling radiation range of UGS on UHI effects is 300 m, and the cooling effect is most effective from 0 to 200 m. The more the UGS is dispersed, the more significant the cooling effect of UGS. Our study demonstrates that the cooling mechanism of UGS on UHI includes radiation range, types and spatial distribution of UGS, and the approach provides a basis for evaluating UHI effects for urban planning.