Mitigation Of Urban Heat Island Effect Research Articles

Temporal Variations in Land Surface Temperature within an Urban Ecosystem: A Comprehensive Assessment of Land Use and Land Cover Change in Kharkiv, Ukraine

Remote sensing technologies are critical for analyzing the escalating impacts of global climate change and increasing urbanization, providing vital insights into land surface temperature (LST), land use and cover (LULC) changes, and the identification of urban heat island (UHI) and surface urban heat island (SUHI) phenomena. This research focuses on the nexus between LULC alterations and variations in LST and air temperature (Tair), with a specific emphasis on the intensified SUHI effect in Kharkiv, Ukraine. Employing an integrated approach, this study analyzes time-series data from Landsat and MODIS satellites, alongside Tair climate records, utilizing machine learning techniques and linear regression analysis. Key findings indicate a statistically significant upward trend in Tair and LST during the summer months from 1984 to 2023, with a notable positive correlation between Tair and LST across both datasets. MODIS data exhibit a stronger correlation (R2 = 0.879) compared to Landsat (R2 = 0.663). The application of a supervised classification through Random Forest algorithms and vegetation indices on LULC data reveals significant alterations: a 70.3% increase in urban land and a decrement in vegetative cover comprising a 15.5% reduction in dense vegetation and a 62.9% decrease in sparse vegetation. Change detection analysis elucidates a 24.6% conversion of sparse vegetation into urban land, underscoring a pronounced trajectory towards urbanization. Temporal and seasonal LST variations across different LULC classes were analyzed using kernel density estimation (KDE) and boxplot analysis. Urban areas and sparse vegetation had the smallest average LST fluctuations, at 2.09 °C and 2.16 °C, respectively, but recorded the most extreme LST values. Water and dense vegetation classes exhibited slightly larger fluctuations of 2.30 °C and 2.24 °C, with the bare land class showing the highest fluctuation 2.46 °C, but fewer extremes. Quantitative analysis with the application of Kolmogorov-Smirnov tests across various LULC classes substantiated the normality of LST distributions p > 0.05 for both monthly and annual datasets. Conversely, the Shapiro-Wilk test validated the normal distribution hypothesis exclusively for monthly data, indicating deviations from normality in the annual data. Thresholded LST classifies urban and bare lands as the warmest classes at 39.51 °C and 38.20 °C, respectively, and classifies water at 35.96 °C, dense vegetation at 35.52 °C, and sparse vegetation 37.71 °C as the coldest, which is a trend that is consistent annually and monthly. The analysis of SUHI effects demonstrates an increasing trend in UHI intensity, with statistical trends indicating a growth in average SUHI values over time. This comprehensive study underscores the critical role of remote sensing in understanding and addressing the impacts of climate change and urbanization on local and global climates, emphasizing the need for sustainable urban planning and green infrastructure to mitigate UHI effects.

Construction of a cold island network for the urban heat island effect mitigation

The urban heat island (UHI) effect seriously challenges sustainable urban development strategies and livability. Numerous studies have explored the UHI problem from the perspective of isolated blue and green patches, ignoring the overall function of cold island networks. This study aims to explore the construction method of cold island network by integrating scattered cold island resources, rationally guiding urban planning and construction, and providing effective ideas and methods for improving the urban thermal environment. Taking the central city of Fuzhou as an example, the identification of the cold island core source (CICS) was optimized by applying relative land surface temperature (LST), morphological spatial pattern analysis, and landscape connectivity analysis. The combined resistance surface was constructed based on a spatial principal component analysis. Subsequently, the cold island network was constructed by applying circuit theory and identifying the key nodes. The results showed that the central and eastern parts of the study area experienced the most significant UHI effects and there was a tendency for them to cluster. Overall, 48 core sources, 104 corridors, 89 cooling nodes, and 34 heating nodes were identified. The average LST of the CICSs was 28.43 °C, significantly lower than the average LST of the entire study area (31.50 °C), and the 104 cold corridors were classified into three categories according to their importance. Different targeting measures should be adopted for the cooling and heating nodes to maintain the stability of the cold island network and prevent the formation of a heat network. Finally, we suggest a model for urban cold island network construction and explore methods for mitigating issues with UHI to achieve proactive and organized adaptation and mitigation of thermal environmental risks in urban areas, as well as to encourage sustainable urban development.

Monitoring of a Living Wall System in Santo Domingo, Dominican Republic, as a Strategy to Reduce the Urban Heat Island

Given the current need to reduce the Urban Heat Island (UHI) worldwide, one of the strategies that can contribute to this mitigation is green façades. In this context, the aim of this research is to evaluate a Living Wall System (LWS) as a strategy to reduce the urban heat island in Santo Domingo, Dominican Republic, using outdoor test cells. This research was focused on the monitoring of two different façades, an LWS and a reference façade, during the warmer months. For the comparison, the parameters measured were air temperature, relative humidity, surface temperature and environmental variables. In addition, thermal images were taken. Results reveal that during the days selected, the average outdoor air temperature difference between the LWS compared to the reference façade was 5.3 °C, whereas during the day, the average was 3.3 °C. Concerning surface temperature, in the case of the LWS, the temperature was higher and had greater fluctuations than the reference façade. This behavior was confirmed by the results obtained with thermal images. In conclusion, using an LWS in a tropical climate helps the urban microclimate, which contributes to urban heat island effect mitigation during the warmer months.

Identification of a wetland ecological network for urban heat island effect mitigation in Changchun, China

The rapid development of cities has led to severe fragmentation of wetland landscapes, destroying their ecological function in climate regulation. However, most studies on the climate regulation services of wetlands focused on isolated wetland units, ignoring the overall function of wetland networks. The climate regulation function of wetlands can be improved by integrating fragmented wetland resources and building a stable wetland network. A case study was carried out in Changchun City, China, to improve the method of identifying ecological networks by considering the network energy flows. First, morphological spatial pattern analysis and landscape connectivity index combined with the wetland cooling index were used to identify ecological sources with high cooling capacity, and an ecological resistance surface was constructed with surface temperature as the main factor. The minimum cumulative resistance model was then used to identify the ecological network, which was then optimized by integrating patches as stepping stones to form the optimized ecological network. Finally, the importance of ecological corridors was evaluated by identifying ventilation corridors and integrated with the complex network theory to determine the ecological network robustness. We found that the degree of fragmentation in the studied wetlands was relatively high, and that construction of an ecological network with patches as stepping stones can improve its robustness. Each component in the ecological network had a high potential to mitigate the urban heat island effect, which can be further promoted by ecological corridors with high ventilation potential. Mutations in ecological nodes that cause network robustness played a key role in maintaining ecological network stability. This improved methodology effectively improves the scientific and practical application of wetland networks to mitigate the urban heat island effect and provides regions facing the contradiction of rapid development and wetland protection with strategies to reduce the threat of this effect.

Role of reservoirs of urban heat island effect mitigation in human settlements: moderate climate zone

Role of reservoirs of urban heat island effect mitigation in human settlements: moderate climate zone

Kentsel Ekolojik Koridor Modeli: Malatya Örneği

Günümüzde kentsel alanlardaki genişleme ekosistem süreçleri üzerinde baskı oluşturmaktadır. Bu baskının saptanması ve kontrol edilmesi için ekoloji tabanlı modeller geliştirilmektedir. Bu noktadan hareketle çalışma, Malatya kenti örneğinde enerji akışını ve doğal tür akışını düzenleyecek, kentsel ısı adası etkisini azaltacak ve habitat bağlanabilirliğini artıracak arazi kullanım politikalarının geliştirilmesine katkı sağlayacak ve kentlere rehberlik edecek bir kentsel ekolojik koridor modeli geliştirmeyi amaçlamaktadır. Belirtilen amaca ulaşmak için farklı ölçek ve zamansallıktaki uydu görüntüleri, iklim verileri, topografik veriler ve demografik veri setleri farklı uzaktan algılama ve coğrafi bilgi sistemleri tekniklerini kullanılarak ilişkilendirilmiş ve kentsel ekolojik koridor modeli oluşturulmuştur.
 Malatya’da 1985-2021 yılları arasında kentsel büyümenin en çok etkilediği ekosistemin tarımsal ekosistem olduğu saptanmıştır. 2050 yılında kentsel nüfus 888.784 kişiye ulaşacağı öngörüsüne dayanarak kentsel alanların 173 km2’ye ulaşacağı tespit edilmiştir. 1985-2021 döneminde olduğu gibi 2021-2050 yılları arasında tarımsal ekosistemler üzerindeki baskı artarak devam ederken ekosistemler arasındaki bağlantı giderek zayıflayacaktır. 
 Ekolojik koridorlar, tarım ve bozkır ekosistemine ait ekolojik açıdan en duyarlı ve en büyük bütünleşik lekeler arasında kentsel yayılmayı yönlendirerek, enerji akışı, doğal tür akışı, kentsel ısı adası etkisinin azaltılması, yeraltı su rejiminin düzenlenmesi ve habitat bağlantılılığı gibi çeşitli ekolojik işlevler üstlenecektir. Malatya’da tarımsal ekosistemden 13 ve bozkır ekosisteminden 5 adet ekolojik açıdan duyarlı leke belirlenmiş ve ekosistem lekelerini birbirlerine bağlayan 694 km2 alana sahip ekolojik koridor önerilmiştir.

Nature-Based Solutions (NBSs) to Mitigate Urban Heat Island (UHI) Effects in Canadian Cities

Canada is warming at double the rate of the global average caused in part to a fast-growing population and large land transformations, where urban surfaces contribute significantly to the urban heat island (UHI) phenomenon. The federal government released the strengthened climate plan in 2020, which emphasizes using nature-based solutions (NBSs) to combat the effects of UHI phenomenon. Here, the effects of two NBSs techniques are reviewed and analysed: increasing surface greenery/vegetation (ISG) and increasing surface reflectivity (ISR). Policymakers have the challenge of selecting appropriate NBSs to meet a wide range of objectives within the urban environment and Canadian-specific knowledge of how NBSs can perform at various scales is lacking. As such, this state-of-the-art review intends to provide a snapshot of the current understanding of the benefits and risks associated with the implantation of NBSs in urban spaces as well as a review of the current techniques used to model, and evaluate the potential effectiveness of UHI under evolving climate conditions. Thus, if NBSs are to be adopted to mitigate UHI effects and extreme summertime temperatures in Canadian municipalities, an integrated, comprehensive analysis of their contributions is needed. As such, developing methods to quantify and evaluate NBSs’ performance and tools for the effective implementation of NBSs are required.

Assessing the potential of strategic green roof implementation for green infrastructure: Insights from Sumida ward, Tokyo

Urban green spaces, and green infrastructure more generally, provide multiple benefits that can enhance urban livability and sustainability. These range from the mitigation of air pollution and urban heat island (UHI) effect, to multi-dimensional benefits to human wellbeing and biodiversity. However, the expansion of urban green spaces is not always feasible in many cities. In such urban contexts, there have been proposals to utilize rooftops as green roofs in order to gain some of these benefits. This study spatially identifies areas where roofs have the potential to provide different types of benefits associated with urban green spaces if they are retrofitted with green roofs. Through a GIS-based approach we catalogue available roof space in Sumida ward in Tokyo for green roof implementation, and subsequenlty evaluate the potential of each roof patch to offer four types of benefits if retrofitted with a green roof, namely UHI effect mitigation, air pollution mitigation, and benefits to subjective wellbeing and biodiversity. Approximately 25% of the total roof surface in Sumida ward can potentially be used for green roof implementation. Furthermore, about 5.2% and 59% of this area has a respectively high and moderate potential to provide all four benefits if retrofitted with green roofs. This could increase the extent of green spaces by 10% and 120% respectively across the Sumida ward. In this sense, green roofs can become a major element of green infrastructure with ripple positive effects for urban livability and sustainability through the provision of UHI effect and air pollution mitigation, and benefits to subjective wellbeing and biodiversity.

Solar energy harvesting pavements on the road: comparative study and performance assessment

• Performance of various solar energy harvesting pavements are compared. • The pavements’ impact on the urban heat island effect is analyzed. • The electricity and heat yields of the pavements are simulated. • The PIPVT module can achieve the average overall energy efficiency of 37.31%. As a significant infrastructure in modern cities, road pavements occupy a great share of urban surfaces and absorb abundant solar radiation. Thus, pavements have tremendous potential in solar energy utilization and can serve as distributed energy generators in smart and sustainable cities. Some solar energy harvesting pavement modules have emerged in recent years, including pavement-integrated photovoltaic (PIPV) module, pavement-integrated solar thermal (PIST) module, and pavement-integrated photovoltaic thermal (PIPVT) module. In this study, for all the above modules, simulations were conducted with the developed and validated two-dimensional transient models on the weather conditions of four typical days in different seasons in Shanghai. Both the operating performance and influence on the urban heat island (UHI) effect were investigated to evaluate and compare their energy performance and effect on urban microclimatic conditions. The results show that the electricity yield of the PIPVT module is slightly higher than that of the PIPV module, while its heat yield is lower than that of the PIST module on all typical days. When considering both electricity and heat yields, the PIPVT module can achieve an average overall energy efficiency of 37.31%. Compared with the conventional pavement module, all three solar energy harvesting pavement modules have lower maximum asphalt average temperatures that can decelerate the thermal aging of asphalt concrete. The PIPVT module has the most significant effect on the reduction of the maximum asphalt average temperature, decreasing it by 10.57°C on average. Additionally, all three solar energy harvesting pavement modules can mitigate the UHI effect, and the PIPVT and PIST modules have the most and the least influence on UHI effect mitigation, respectively.

Quantifying the Albedo of the Montreal Island and its Potential for Increase

Urbanization has changed the Earth’s surface, resulting in the urban heat island effect. There has been a recent focus on increasing urban albedo as a strategy to mitigate this phenomenon. Studies on Montreal’s albedo have primarily looked at the impact of albedo manipulations upon the urban heat island effect. However, the current albedo of the island, broken down by land use type, has yet to be quantified. Therefore, previous studies often rely on generalized urban albedo and land use estimates that have not been proven to be generalizable to Montreal. This study attempted to quantify the current albedo of the Island of Montreal through urban land use categorization. The findings were then used to estimate albedo increase under different roof replacement scenarios. Data sets for building footprints, vegetation, and roadways were incomplete in Montreal, requiring the combination of several sources to obtain representative data for analysis. This study found the albedo of Montreal island to be 0.19 ± 0.057. Further, the hypothetical roof change scenarios then aligned with a 0.1 albedo increase, which is the albedo change used in current urban heat island effect mitigation literature. Using the albedo increase potential that resulted from the three scenarios tested here, future research should explore further estimation of the associated surface and air temperature decrease.

Spatial patterns and temporal variations of footprint and intensity of surface urban heat island in 141 China cities

l We investigated the spatial patterns and temporal variations of footprint (FP) and intensity of surface urban heat island (SUHI) in 141 China cities. l With the increase of city size, FP showed an increasing trend in medium and small cities, but plateaued in big cities. l SUHI intensity presented spatial and seasonal variations in daytime and nighttime across cities in different climatic zones. l This study is of great help for developing mitigating strategies of SUHI effect in cities with different urbanized levels or climatic background. An improved understanding of urban heat island (UHI) is important in urban ecological and environmental studies. In this study, we investigated footprint (FP) and intensity of surface UHI (SUHI) from 2003 to 2020 in 141 China cities using a Gaussian model and multi-source remote sensing data. Results showed that annual daytime FP in 79% cities was larger than nighttime FP. There were more cities having larger daytime FP than nighttime FP in summer compared to other seasons. With the increase of city size, FP showed an increasing tendency in median or small cities, while plateaued in large cities. We also found that high SUHI intensity occurred in cities with warm climate in daytime but occurred in cities with cold climate in nighttime. Moreover, SUHI intensity in daytime was higher than that of nighttime in all climatic zones in summer, while in other seasons, SUHI intensity in daytime was higher than that of nighttime only in warm climatic zones. Finally, 96% cities showed higher SUHI intensity in daytime than that of nighttime in summer, while proportion of such cities was only 45% in winter. Findings of this study are helpful for mitigating UHI effect in cities with different urbanized levels or climatic background.

Synergy of reduced graphene oxide and metal oxides improves the power factor of thermoelectric cement matrix composites

Thermoelectric cement, a functional material that realizes the mutual conversion of thermal and electrical energy, has wide application prospects in energy harvesting and urban heat island effect mitigation. In this article, metal oxides and reduced graphene oxide (RGO) were added through ethanol liquid-phase mixing and pre-dispersion processes to the cement-based composites to enhance the thermoelectric properties. The addition of metal oxide increases the metal oxide/cement interface (metal oxide to cement interface, metal oxide to RGO interface, etc.). The presence of high-density interfaces hinders the carrier motion and leads to carrier scattering at the interfaces, which enhances the Seebeck effect of cement matrix composites. When the TiO2 content is 10.0 wt%, the RGO cement matrix composite achieved a power factor (PF) of 1.23 μWm−1 K−2, which was 10 times higher than before the addition. This study is a novel idea for further improving the thermoelectric properties of cementitious composites and promoting their practical applications.

Estimating spatial and temporal patterns of urban building anthropogenic heat using a bottom-up city building heat emission model

Anthropogenic heat (AH) emission from buildings is a key contributor to the urban heat island (UHI) effect. Although an improved understanding of spatiotemporal patterns of building AH is highly needed for mitigating UHI effect, such information is still limited in high spatiotemporal resolutions at the city level. In this study, a bottom-up city building heat emission model (CityBHEM) was developed to investigate temporal variations of building AH from three components (i.e., envelope convection, zone infiltration and exfiltration, and HVAC system) for all buildings in Boston, United States. First, buildings in Boston were grouped into eleven commercial and five residential building prototypes based on building type, construction year, and foundation type. Second, an end-use-based calibration was developed to calibrate CityBHEM using U.S. Energy Information Administration's survey data. Finally, AH from all buildings in the city under actual weather conditions was calculated using the calibrated CityBHEM model together with building types and sizes. Results indicate that total building AH density of Back Bay neighborhood reaches the maximum value of 526 kWh/m2 in summer (56% of HVAC system and 44% of envelope convection) and the minimum value of 369 kWh/m2 in winter (54% of HVAC system, 24% of envelope convection and 22% of zone infiltration and exfiltration). In contrast, total building AH density of suburban neighborhoods is lower than 30 kWh/m2 in summer and 20 kWh/m2 in winter. Given that key inputs are publicly available, CityBHEM is transferable to other U.S. cities, enabling us to explore practical building energy-saving strategies for mitigating AH.

Exploring DAD and ADD Methods for Dealing with Urban Heat Island Effect

The Urban Heat Island (UHI) effect in the context of climate change and temperature fluctuations is an increasing challenge for contemporary cities. Numerous activities focus on mitigation and adaptation to the UHI effect using both appropriately selected design strategies and technological solutions. However, not all of these technologies support the postulates of ecological and low-carbon cities. Their design, implementation, and operation process sometimes causes conflicts or misunderstandings among designers, industry engineers, and residents. The aim of the research was to examine the relationship between UHI effect mitigation, adaptation, and energy efficiency strategies. A further goal was to build a matrix of synergistic elements and conflicts for respective actors and stakeholders, and an analysis of the elitist DAD (Decide-Announce-Defend) method and participatory ADD (Announce-Discuss-Decide) or EDD (Engage-Deliberate-Decide) in dealing with the UHI effect. The literature review and case study analysis methods were applied. In the study, the strategies of five chosen European capitals (Berlin, London, Paris, Vienna, and Warsaw) experiencing a UHI problem were analyzed. As result, a matrix of the most common goal differences of respective stakeholders in dealing with the UHI effect was developed. One of the main conclusions is the necessity of undergoing synergic collaboration between actors that are not cooperating yet, combined with risk analysis and appropriate education at different levels for a successful and socially equal mitigation and adaptation to the UHI effect.

Enhanced thermoelectric performance of low carbon cement-based composites by reduced graphene oxide

Cement-based composites with thermoelectric effect have broad application prospects in the fields of urban heat island effect mitigation, winter road snow melting and ice melting and energy harvesting. Although cement-based composites have made great strides in terms of thermoelectric properties, the high carbon content makes their mechanical properties low, this is the main obstacle to further improvement of thermoelectric performance. In this paper, we added reduced graphene oxide (RGO) to cement through a liquid-phase mixing process to make cement particles adhere to RGO flakes, which effectively reduced the degree of mutual agglomeration between the RGO and improves the dispersion effect of RGO in cement-based materials. When the RGO content is 5.0 wt%, it has higher electrical conductivity (2.01 S/cm) compared with the RGO cement-based composite prepared by the ball milling process, achieve the ZTmax value of 0.23 × 10−4, and have good temperature stability with the highest output power of 8.27 × 10−3 mW/m2. This facilitates large-scale energy harvesting using thermoelectric cement-based composites.

Utilizing the theory of planned behavior to predict willingness to pay for urban heat island effect mitigation

Mitigation of the urban heat island effect is essential for the sustainable development of China's large cities and public acceptance. There has been limited attention on the economic benefits of mitigating this phenomenon. This research investigates residents' willingness to pay (WTP) for permeable pavement construction to mitigate urban heat impacts and examine the drivers of WTP intention. 799 urban residents of Guangdong Province responded to an online questionnaire. WTP was elicited using the contingent valuation method and WTP intention was explored by establishing structural equation modelling based on the extended theory of planned behavior (TPB). The findings show that the mean WTP was 17.98 Chinese Yuan per month and the extended TPB – with added moral norm – increased the model's ability to explain WTP intention. The perceived behavior control, attitude, and moral norm were major predictors while constructs of a subjective norm show no significant influence on WTP intention. Using the Internet, and especially mobile devices, to popularize related knowledge might be a feasible strategy to promote public awareness of and participation in urban heat island mitigation in the future.

Mismatch of regulating ecosystem services for sustainable urban planning: PM10 removal and urban heat island effect mitigation in the municipality of Rome (Italy)

Balancing the ecosystem service (ES) mismatch should be a goal of sustainable urban planning. However, (i) many urban areas lack an assessment of this mismatch and (ii) scientific findings are not easily translatable into good practices. In this study, we assessed the mismatch for two regulating ESs—regulation of air quality (intended as PM10 removal by vegetation) and urban temperature regulation—in the Municipality of Rome (Italy). The spatial distribution of the ES mismatch was then used to identify priority intervention areas (PIAs), namely those that would benefit the most from targeted urban planning. To do so, we computed composite indicators of supply and demand for each ES, adopting a process-based approach. Additionally, a monetary valuation of the related benefits associated with urban green infrastructure is provided. Our findings suggest that regulation of air quality falls short in highly urbanized areas, whereas a mismatch in urban temperature regulation is observed in both highly urbanized areas and some agricultural lands. The majority of the PIAs fall in the eastern and southern sectors of the Municipality of Rome. Our findings also indicate that urban planning should consider urban regeneration practices and reforestation of existing green areas within the PIAs. Sustainable urban planning can produce remarkable environmental benefits, as estimated, for the Municipality of Rome, up to several hundred million euros per year, depending on the methodology used for the monetary valuation.

Spatio-Temporal Relationship between Land Cover and Land Surface Temperature in Urban Areas: A Case Study in Geneva and Paris

Currently, more than half of the world’s population lives in cities, which leads to major changes in land use and land surface temperature (LST). The associated urban heat island (UHI) effects have multiple impacts on energy consumption and human health. A better understanding of how different land covers affect LST is necessary for mitigating adverse impacts, and supporting urban planning and public health management. This study explores a distance-based, a grid-based and a point-based analysis to investigate the influence of impervious surfaces, green area and waterbodies on LST, from large (distance and grid based analysis with 400 m grids) to smaller (point based analysis with 30 m grids) scale in the two mid-latitude cities of Paris and Geneva. The results at large scale confirm that the highest LST was observed in the city centers. A significantly positive correlation was observed between LST and impervious surface density. An anticorrelation between LST and green area density was observed in Paris. The spatial lag model was used to explore the spatial correlation among LST, NDBI, NDVI and MNDWI on a smaller scale. Inverse correlations between LST and NDVI and MNDWI, respectively, were observed. We conclude that waterbodies display the greatest mitigation on LST and UHI effects both on the large and smaller scale. Green areas play an important role in cooling effects on the smaller scale. An increase of evenly distributed green area and waterbodies in urban areas is suggested to lower LST and mitigate UHI effects.

Sensitivity Study of Weather Research and Forecasting Physical Schemes and Evaluation of Cool Coating Effects in Singapore by Weather Research and Forecasting Coupled with Urban Canopy Model Simulations

AbstractMesoscale 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.

Examining the nexus between land surface temperature and urban growth in Chattogram Metropolitan Area of Bangladesh using long term Landsat series data

In this study, we assessed the impact of Land-Use/ Land-Cover (LULC) changes on Land Surface Temperature (LST) in Chattogram Metropolitan Area (CMA) of southeastern Bangladesh. Landsat-5 TM and Landsat-8 OLI images were used to extract six dominant LULC categories and LST over a 28-years period. The Random Forest classifier was applied to derive LULC categories, whereas the Single-Channel and the Split-Window algorithms were applied to extract LST for the respective years. Three bio-physical parameters such as Normalized Difference Vegetation Index (NDVI), Modified Normalized Difference Water Index (MNDWI) and Normalized Difference Built-up Index (NDBI) representing three dominant LULC categories were extracted from the images to assess their interaction with the LST. Further, the Urban Heat Island (UHI) effect was calculated to assess the impact of LULC changes on the UHI distribution. Additionally, the class level matrices were extracted to assess their relationship with LST and UHI and these were further used in the development of a mathematical model to provide a probable solution for mitigating UHI effect. The result depicted that the urban area (built-up area and impervious surface) in CMA is increasing with a considerable rate (3.55 km2/yr.). The mean LST of the urban area continued to increase from 1990 (20.17 °C) to 2018 (25.83 °C) and the period 2000–2010 experienced the highest rise of LST (normalized LST difference + 0.94 °C) in the study area. The relationship between the studied biophysical indices and LST showed that NDBI positively affects the LST. Further, the analysis of UHI effect showed the number of growing administrative units in terms of intensifying LST which could be reduced by increasing urban patch numbers and edge perimeter with decreasing urban patch size.