scholarly journals Development of a Zero-Dimensional Mesoscale Thermal Model for Urban Climate

2009 ◽  
Vol 48 (3) ◽  
pp. 657-668 ◽  
Author(s):  
Humberto R. Silva ◽  
Rahul Bhardwaj ◽  
Patrick E. Phelan ◽  
Jay S. Golden ◽  
Susanne Grossman-Clarke
Keyword(s):  
Energy Balance ◽  
Urban Heat Island ◽  
Mitigation Strategies ◽  
Anthropogenic Heat ◽  
Mitigation Measures ◽  
Balance Model ◽  
Time Range ◽  
Heat Island ◽  
Time Step ◽  
Urban Heat

Abstract A simple energy balance model is created for use in developing mitigation strategies for the urban heat island effect. The model is initially applied to the city of Phoenix, Arizona. There are six primary contributions to the overall energy balance: incident solar radiation, anthropogenic heat input, conduction heat loss, outgoing evapotranspiration, outgoing convection, and outgoing emitted radiation. Meteorological data are input to the model, which then computes an urban characteristic temperature at a calculated time step for a specified time range. The model temperature is shown to have the same periodic behavior as the experimentally measured air temperatures. Predicted temperature changes, caused by increasing the average urban albedo, agree within 0.1°C with comparable maximum surface temperature predictions from the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5). The present model, while maintaining valid energy-balance physics, allows users to quickly and easily predict the relative effects of urban heat island mitigation measures. Representative mitigation strategies, namely changes in average albedo and long-wavelength emissivity are presented here. Increasing the albedo leads to the greater reduction in daytime maximum temperatures; increasing the emissivity leads to a greater reduction in nighttime minimum temperatures.

scholarly journals Nocturnal Surface Urban Heat Island over Greater Cairo: Spatial Morphology, Temporal Trends and Links to Land-Atmosphere Influences

2020 ◽  
Vol 12 (23) ◽  
pp. 3889
Author(s):  
Ahmed M. El Kenawy ◽  
Mohamed Hereher ◽  
Sayed M. Robaa ◽  
Matthew F. McCabe ◽  
Juan I. Lopez-Moreno ◽  
...  
Keyword(s):  
Urban Heat Island ◽  
Surface Albedo ◽  
Temporal Trends ◽  
Mitigation Strategies ◽  
Cold Spot ◽  
Heat Island ◽  
Time Step ◽  
Greater Cairo ◽  
Urban Heat ◽  
Surface Urban Heat Island

This study assesses the spatial and temporal characteristics of nighttime surface urban heat island (SUHI) effects over Greater Cairo: the largest metropolitan area in Africa. This study employed nighttime land surface temperature (LST) data at 1 km resolution from the Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua sensor for the period 2003–2019. We presented a new spatial anomaly algorithm, which allowed to define SUHI using the most anomalous hotspot and cold spot of LST for each time step over Greater Cairo between 2003 and 2019. Results demonstrate that although there is a significant increase in the spatial extent of SUHI over the past two decades, a significant decrease in the mean and maximum intensities of SUHI was noted. Moreover, we examined the dependency between SUHI characteristics and related factors that influence energy and heat fluxes between atmosphere and land in urban environments (e.g., surface albedo, vegetation cover, climate variability, and land cover/use changes). Results demonstrate that the decrease in the intensity of SUHI was mainly guided by a stronger warming in daytime and nighttime LST in the neighborhood of urban localities. This warming was accompanied by a decrease in surface albedo and diurnal temperature range (DTR) over these areas. Results of this study can provide guidance to local urban planners and decision-makers to adopt more effective mitigation strategies to diminish the negative impacts of urban warming on natural and human environments.

scholarly journals Mitigation measures for urban heat island and their impact on pedestrian thermal comfort

2021 ◽  
Vol 2069 (1) ◽  
pp. 012058
Author(s):  
A Kubilay ◽  
D Strebel ◽  
D Derome ◽  
J Carmeliet
Keyword(s):  
Thermal Comfort ◽  
Urban Heat Island ◽  
Coupled Model ◽  
Mitigation Strategies ◽  
Mitigation Measures ◽  
Heat Island ◽  
Heat And Moisture Transport ◽  
Urban Heat ◽  
Urban Square ◽  
Heat And Moisture

Abstract A multiscale coupled model is presented that allows for the detailed analysis of the local impact of urban heat island mitigation measures. The model uses coupled computational fluid dynamics (CFD) simulations with unsteady heat and moisture transport (HAM) in porous urban materials in order to take into account the dynamic heat and moisture storage in the built environment. A realistic case study is performed for a public urban square in the City of Zurich during heat wave conditions. The impacts of two different mitigation strategies, i.e. adding artificial wetting of pavements and adding vegetation, on pedestrian thermal comfort are evaluated and compared with the existing situation. The results show an improvement in thermal comfort in both conditions. The improvement resulting from the addition of trees is larger and lasts longer due to shadowing effects, even though a reduced ventilation and an increased relative humidity by trees have an adverse effect on the thermal comfort.

scholarly journals Willingness to Pay for Urban Heat Island Mitigation: A Case Study of Singapore

Climate ◽  
2020 ◽  
Vol 8 (7) ◽  
pp. 82
Author(s):  
Natalia Borzino ◽  
Samuel Chng ◽  
Muhammad Omer Mughal ◽  
Renate Schubert
Keyword(s):  
Willingness To Pay ◽  
Urban Heat Island ◽  
Survey Design ◽  
Mitigation Strategies ◽  
Mitigation Measures ◽  
Heat Island ◽  
Related Information ◽  
Policy Interventions ◽  
Positive Attitudes ◽  
Urban Heat

In many countries, urban heat island (UHI) effects come along with urbanization in metropolitan areas. They have relevant adverse effects on the health and wellbeing of citizens. Singapore is strongly affected by UHI. In this study, we assess Singaporeans’ willingness to pay (WTP) for UHI mitigation by implementing a contingent valuation analysis. Specifically, we employ a double-bounded dichotomous survey design on a representative sample of 1822 online respondents. We find that Singaporeans are willing to sacrifice on average 0.43% of their annual income to mitigate UHI. The total WTP for mitigation strategies among Singapore citizens and permanent residents is estimated at SGD$783.08 million per year, the equivalent of USD$563.80 per year. Our findings suggest that there is a positive and significant relationship between the size of UHI effects and the citizens’ WTP. People living in the region with the highest intensity of UHI are willing to pay 3.09 times more than those living in the region with the lowest UHI intensity. Furthermore, demographic and socio-economic characteristics are significant determinants of Singaporeans’ WTP. The WTP increases with income and education but decreases with age. Students, men, and people with children are willing to pay more. Additional analyses show that the level of UHI awareness, positive attitudes towards UHI mitigation strategies as well as preferences for outdoor activities are positively correlated with the WTP. Our findings suggest that citizens are aware of the impacts of UHI and support UHI mitigation measures to be financed by their taxes. Policy interventions to promote UHI-related education and disseminating UHI-related information might increase the support of UHI mitigation policies.

Quantifying the contribution of land use change to the surface urban heat island in China

2020 ◽  
Author(s):  
Zhi Qiao ◽  
Luo Liu ◽  
Dongrui Han ◽  
Zongyao Sun ◽  
Xinliang Xu
Keyword(s):  
Land Use ◽  
Land Use Change ◽  
Urban Heat Island ◽  
Anthropogenic Heat ◽  
Mitigation Measures ◽  
Practical Significance ◽  
Heat Island ◽  
Land Use Types ◽  
Urban Heat ◽  
The Impact

<p>Urban Heat Island (UHI), a phenomenon characterized by significantly higher air and land surface temperatures (LSTs) in urban areas than in suburban areas, results in land use change from non-urban to urban land and is accompanied by increases in anthropogenic heat release. A variety of land use contribution indexes have been proposed to quantitatively calculate the impact of land use types on UHI. However, these indexes can only show the impact of specific land use types on UHI. In fact, the area and the intensity (which also can be considered as the average temperature) of land use change jointly determine the regional UHI. The purpose of this paper is to develop an algorithm to quantitatively reveal the influence of the area and the intensity of land use change on regional UHI. MODIS LST products and 1:1,000,000 land use data sets were used to quantitatively calculate the seasonal and interannual contributions of land use change on regional UHI between 2005 and 2018 in China. These results have theoretical and practical significance for further understanding the formation mechanism of urban thermal environment and its mitigation measures.</p>

scholarly journals Quantitative Analysis of Factors Contributing to Urban Heat Island Intensity

2012 ◽  
Vol 51 (5) ◽  
pp. 842-854 ◽  
Author(s):  
Young-Hee Ryu ◽  
Jong-Jin Baik
Keyword(s):  
Urban Heat Island ◽  
Single Layer ◽  
Anthropogenic Heat ◽  
Heat Island ◽  
Impervious Surfaces ◽  
Additional Heat ◽  
Urban Geometry ◽  
Causative Factors ◽  
Urban Heat ◽  
Vertical Walls

AbstractThis study identifies causative factors of the urban heat island (UHI) and quantifies their relative contributions to the daytime and nighttime UHI intensities using a mesoscale atmospheric model that includes a single-layer urban canopy model. A midlatitude city and summertime conditions are considered. Three main causative factors are identified: anthropogenic heat, impervious surfaces, and three-dimensional (3D) urban geometry. Furthermore, the 3D urban geometry factor is subdivided into three subfactors: additional heat stored in vertical walls, radiation trapping, and wind speed reduction. To separate the contributions of the factors and interactions between the factors, a factor separation analysis is performed. In the daytime, the impervious surfaces contribute most to the UHI intensity. The anthropogenic heat contributes positively to the UHI intensity, whereas the 3D urban geometry contributes negatively. In the nighttime, the anthropogenic heat itself contributes most to the UHI intensity, although it interacts strongly with other factors. The factor that contributes the second most is the impervious-surfaces factor. The 3D urban geometry contributes positively to the nighttime UHI intensity. Among the 3D urban geometry subfactors, the additional heat stored in vertical walls contributes most to both the daytime and nighttime UHI intensities. Extensive sensitivity experiments to anthropogenic heat intensity and urban surface parameters show that the relative importance and ranking order of the contributions are similar to those in the control experiment.

scholarly journals Combating Urban Heat Island Effect—A Review of Reflective Pavements and Tree Shading Strategies

Buildings ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 93
Author(s):  
V. R. Sankar Cheela ◽  
Michele John ◽  
Wahidul Biswas ◽  
Prabir Sarker
Keyword(s):  
Urban Heat Island ◽  
Urban Forest ◽  
Critical Role ◽  
Tree Canopy ◽  
Mitigation Measures ◽  
Heat Island ◽  
Human Thermal Comfort ◽  
Urban Heat ◽  
Pavement Temperature ◽  
Reflective Coatings

Pavements occupy about 40% of urban land cover, with 75–80% black top roads, playing a critical role in urban connectivity and mobility. Solar energy is absorbed and stored in pavements leading to an increase in surface temperatures. Decreasing green cover is further contributing to rise in regional temperatures. Due to this activity, the city experiences urban heat island (UHI). This study presents a critical review of the literature on mitigation measures to combat UHI using reflective pavements with an emphasis on durability properties and impacts of tree canopy. The strategies with a focus on application of chip seals, white toppings, and coatings were discussed. Role of surface reflectance, including those from asphalt and concrete pavements, albedo improvements, and technological trends, application of waste materials, and industrial by‐products are presented. Also, urban tree shading systems’ contribution to pavement temperature and microclimate systems is presented. The review shows that the development of mitigation measures using tree shading systems can reduce the pavement temperature during daytime and increase human thermal comfort. The outcomes of this review provide a scope for future studies to develop sustainable and state‐of‐the-art engineering solutions in the field of reflective coatings and urban forest systems.

scholarly journals A High-Resolution Monitoring Approach of Canopy Urban Heat Island using Random Forest Model and Multi-platform Observations

2021 ◽  
Author(s):  
Shihan Chen ◽  
Yuanjian Yang ◽  
Fei Deng ◽  
Yanhao Zhang ◽  
Duanyang Liu ◽  
...  
Keyword(s):  
High Resolution ◽  
Random Forest ◽  
Urban Heat Island ◽  
Air Temperature ◽  
Anthropogenic Heat ◽  
Heat Island ◽  
Model Framework ◽  
Rapid Urbanization ◽  
Urban Heat ◽  
The City

Abstract. Due to rapid urbanization and intense human activities, the urban heat island (UHI) effect has become a more concerning climatic and environmental issue. A high spatial resolution canopy UHI monitoring method would help better understand the urban thermal environment. Taking the city of Nanjing in China as an example, we propose a method for evaluating canopy UHI intensity (CUHII) at high resolution by using remote sensing data and machine learning with a Random Forest (RF) model. Firstly, the observed environmental parameters [e.g., surface albedo, land use/land cover, impervious surface, and anthropogenic heat flux (AHF)] around densely distributed meteorological stations were extracted from satellite images. These parameters were used as independent variables to construct an RF model for predicting air temperature. The correlation coefficient between the predicted and observed air temperature in the test set was 0.73, and the average root-mean-square error was 0.72 °C. Then, the spatial distribution of CUHII was evaluated at 30-m resolution based on the output of the RF model. We found that wind speed was negatively correlated with CUHII, and wind direction was strongly correlated with the CUHII offset direction. The CUHII reduced with the distance to the city center, due to the de-creasing proportion of built-up areas and reduced AHF in the same direction. The RF model framework developed for real-time monitoring and assessment of high-resolution CUHII provides scientific support for studying the changes and causes of CUHII, as well as the spatial pattern of urban thermal environments.

scholarly journals Green Infrastructure as an Urban Heat Island Mitigation Strategy—A Review

Water ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 3577
Author(s):  
Fatma Balany ◽  
Anne WM Ng ◽  
Nitin Muttil ◽  
Shobha Muthukumaran ◽  
Man Sing Wong
Keyword(s):  
Thermal Comfort ◽  
Urban Heat Island ◽  
Green Infrastructure ◽  
Mitigation Strategies ◽  
Heat Island ◽  
Recent Past ◽  
Simulation Tools ◽  
Human Thermal Comfort ◽  
Different Types ◽  
Urban Heat

Research on urban heat mitigation has been growing in recent years with many of the studies focusing on green infrastructure (GI) as a strategy to mitigate the adverse effects of an urban heat island (UHI). This paper aims at presenting a review of the range of findings from GI research for urban heat mitigation through a review of scientific articles published during the years 2009–2020. This research includes a review of the different types of GI and its contribution for urban heat mitigation and human thermal comfort. In addition to analysing different mitigation strategies, numerical simulation tools that are commonly used are also reviewed. It is seen that ENVI-met is one of the modelling tools that is considered as a reliable to simulate different mitigation strategies and hence has been widely used in the recent past. Considering its popularity in urban microclimate studies, this article also provides a review of ENVI-met simulation results that were reported in the reviewed papers. It was observed that the majority of the research was conducted on a limited spatial scale and focused on temperature and human thermal comfort.

scholarly journals Spatial and Temporal Structure of the Urban Heat Island in Seoul

2005 ◽  
Vol 44 (5) ◽  
pp. 591-605 ◽  
Author(s):  
Yeon-Hee Kim ◽  
Jong-Jin Baik
Keyword(s):  
Urban Heat Island ◽  
Temporal Structure ◽  
Temperature Data ◽  
Total Variance ◽  
Anthropogenic Heat ◽  
Urban Heat Island Intensity ◽  
Heat Island ◽  
Near Surface ◽  
Average Maximum ◽  
Urban Heat

Abstract The spatial and temporal structure of the urban heat island in Seoul, Korea, is investigated using near-surface temperature data measured at 31 automatic weather stations (AWSs) in the Seoul metropolitan area for the 1-yr period from March 2001 to February 2002. The urban heat island in Seoul deviates considerably from an idealized, concentric heat island structure, mainly because of the location of the main commercial and industrial sectors and the local topography. Relatively warm regions extend in the east–west direction and relatively cold regions are located near the northern and southern mountains. Several warm cores are observed whose intensity, size, and location are found to vary seasonally and diurnally. Similar to previous studies, the urban heat island in Seoul is stronger in the nighttime than in the daytime and decreases with increasing wind speed and cloud cover, but it is least developed in summer. The average maximum urban heat island intensity is 2.2°C over the 1-yr period and it is 3.4°C at 0300 local standard time (LST) and 0.6°C at 1500 LST. The reversed urban heat island is occasionally observed in the afternoon, but its intensity is very weak. An empirical orthogonal function (EOF) analysis is performed to find the dominant modes of variability in the Seoul urban heat island. In the analysis using temperature data that are averaged for each hour of the 1-yr period, the first EOF explains 80.6% of the total variance and is a major diurnal mode. The second EOF, whose horizontal structure is positive in the eastern part of Seoul and is negative in the western part, explains 16.0% of the total variance. This mode is related to the land use type and the diurnal pattern of anthropogenic heat release. In the analysis using temperature data at 0300 LST, the leading four modes explain 72.4% of the total variance. The first EOF reflects that the weakest urban heat island intensity is in summer. It is found that the urban heat island in Seoul is stronger on weekdays than weekends.

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