Urban Heat Island: Urban analysis, assessment and measuring mitigation in cities of extreme dry weather (2024)

International Journal of Biometeorology, 2014

Biomimetics

In recent years, demographic growth has caused cities to expand their urban areas, increasing the risk of overheating, creating insurmountable microclimatic conditions within the urban area, which is why studies have been carried out on the urban heat island effect (UHI) and its mitigation. Therefore, this research aims to evaluate the cooling potential in the application of strategies based on biomimicry for the microclimate in a historical heritage city of Panama. For this, three case studies (base case, case 1, and case 2) of outdoor thermal comfort were evaluated, in which the Envi-met software was used to emulate and evaluate the thermal performance of these strategies during March (highest temperature month) and October (rainier month). The strategies used were extracted from the contrast of zebra skin, human skin, evaporative cooling, and ant skin. The results showed a reduction of 2.8 °C in the air temperature at 11:00, the radiant temperature decreased by 2.2 °C, and the PE...

Building and Environment, 2020

A B S T R A C T Urban heat island (UHI) has been evidenced as a phenomenon having a series of negative consequences in energy use, human thermal comfort, citizens' health, wellbeing and air quality. Thus, all professions, faculties and disciplines of society are actively seeking for effective UHI mitigation techniques and strategies. Previous studies have indicated that synoptic variables such as wind, precipitation, cloud coverage, fog and air quality have significant impacts on UHI phenomenon. In accordance with this basis, we devise to develop UHI mitigation techniques and strategies based on meteorological characteristics and synoptic conditions. This paper therefore has reviewed the influences of meteorological characteristics and synoptic conditions, such as precipitation, wind, cloud coverage, fog, air pollution and haze on UHI effects. Through this work, people can obtain better understandings of using them to mitigate UHI effects. Meanwhile, some suggestions on urban planning and development have been briefly presented for the alle-viation of UHI effects.

Journal of Environmental Quality, 2016

The warning of urban air has been documented to increase in intensity and area as cities grow (Oke, 1982). As the cities grow the so called " heat island " tends to increase the risk of more frequent heat waves as well as their impacts (IPCC, 2001). Threshold values to define a heat wave vary geographically. For the case of Mexico City located in a high inland valley in the tropics, values above 30° C (daily maximum observed for three or more consecutive days and 25° C or more as mean temperature) have been adopted to define the phenomenon. These events occur at the end of the dry season during March to May when afternoon relative humidity is quite low (∼20%) and thus reducing the stress. Maximum temperatute data from the Observatory of the National Meteorological Service were used. Results show that during the second half of the XXth century the frequency of heat waves as defined above has doubled from 6 events/decade to 16/decade in the 1990s with a marked increase in the last third of the last century when population of the city grew from 8.5 to 18.5 million (CONAPO, 2000). During this time the average urban/rural contrast grew considerably from about 6° C to 10° C (Jáuregui, 1986). While these heat waves may be considered as " mild " they receive attention from the media and prompt actions by the population to relieve the heat stress. Application of heat indices based on the human energy balance (PET and PMV) result in moderate to strong heat stress during these events. Because climate change is expected to raise night-time minimum temperatures more than daytime highs (as suggested by the IPCC, 2001) urban heat islands and their related heat waves are likely to be a significant health concern in days to come in large urban centers especially in the developing countries.

Environmental Earth Sciences

The aim of the study is, therefore, to analyze the formation of the UHIs in eight different cities in arid and semi-arid regions. The analysis is based on land cover (LC) classification (urban, green, and bare areas). The study found that bare areas had the highest mean LST values compared to the urban and green areas. The results show that the difference in temperatures between the bare areas and the urban areas ranges between 1 and 2°C, between the bare areas and green areas ranges between 1 and 7°C, and between the urban areas and green areas ranges between 1 and 5°C. Furthermore, the LST values varied for each of the LULC categories, and hence some areas in the three categories had lower or higher LST values than in other categories. Hence, one category may not always have the highest LST value compared to other categories. The outcomes of this study may, therefore, have critical implications for urban planners who seek to mitigate UHI effects in arid and semi-arid urban areas.

The formation of an urban heat island (UHI) is one of the most common impacts of the urbanization process. To mitigate the effects of UHI, the planning of urban forests (e.g., creation of parks, forests and afforestation streets) has been the major tool applied in this context. Thus, the aim of this study is to evaluate the spatial and temporal distribution of heat islands in Vila Velha, ES, Brazil using the mono-window algorithm. The study followed these methodological steps: 1) mapping of urban green areas through a photointerpretation screen; 2) application of the mono-window algorithm to obtain the spatial and temporal patterns of land surface temperature (LST); 3) correlation between LST and the normalized difference vegetation index (NDVI) and normalized difference build-up index (NDBI); 4) application of ecological evaluation index. The results showed that the mean values of LST in urban areas were at least 2.34 to 7.19 °C higher than undeveloped areas. Moreover, the positive correlation between LST and NDBI showed an amplifying effect of the developed areas for UHI, while areas with a predominance of vegetation attenuated the effect of UHI. Urban centers, clustered in some parts of the j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / s c i t o t e n v city, received the worst ecological assessment index. Finally, the adoption of measures to guide the urban forest planning within urban centers is necessary to mitigate the effect of heat islands and provide thermal comfort in urban areas.

High temperature in the city centers than its' surroundings known as the Urban Heat Island (UHI) effect, which is causing discomfort to the urban dwellers in the summer time is gaining much attention around the world because the world is getting urbanized as it advances in technology. Alterations of surface area, improper urban planning, air pollution, etc. are causing this increasingly growing phenomenon and it is accountable for human discomfort, human casualties and decline of climate. In this paper, an attempt has been taken to review various measures to encounter UHI effect and the processes by which these strategies work is described with diagrams. Using high albedo materials and pavements, green vegetation and green roofs, urban planning, pervious pavements, shade trees and existence of water bodies in city areas are the potential UHI mitigation strategies on which discussion is done in this paper with their limitations. Green vegetation seems to be the most effective measure and other strategies can play a major role under proper condition.

eng.ukm.my

The urban air temperature is gradually rising in all cities in the world. Several factors become the cause of it, such as diminishing of green area, low wind velocity due to high-building density and change of street surface coating materials. Globally, urban footprint only accounts for approximately 2% of the planetary surface. It was well documented that with the rapid urbanization and population growth, increase in built-up land and replace of natural lands with articial buildings altered surface energy budgets, the hydrological cycle, and may affect local, regional and global climate by changing the surface physical properties. Thus, understanding the role of urban land-use and its impact on the climate system is of interest in the context of global warming. Over the past decades worldwide urbanization and climate change have been two interconnected processes describing the role of human activities in altering and modifying the climate system, which, in turn, may result in uncertain feedback of human welfare. When interpreting the complicated relationship between urbanization and climate change, one of the most well-studied and familiar manifestation of urban climate modication is the urban heat island.

Geographia Polonica, Volume 87, Issue 4, 2014

A central strand of research work in the realm of urban physics aims at a better understanding of the variance in microclimatic conditions due to factors such as building agglomeration density, anthropogenic heat production, traffic intensity, presence and extent of green areas and bodies of water, etc. This research has been motivated in part by phenomena associated with climate change and urban heat islands (UHI) and their implications for the urban microclimate. Note that the characteristics and evolution of the urban microclimate is not only relevant to people's experience of outdoor thermal conditions in the cities. It can be argued that the solid understanding of the temporal and spatial variance of urban microclimate represents a prerequisite for the reliable assessment of the thermal performance of buildings (energy requirements, indoor thermal conditions). In this context, the present paper entails a three-fold contribution. First, the existence and extent of the UHI phenomena are documented for a number of Central-European cities. Second, a number of variables of the urban environment are identified that are hypothesized to influence UHI and the urban microclimate variance. These variables, which pertain to both geometric (morphological) and semantic (material-related) urban features are captured within a formal and systematic framework. Third, to support the process of design and evaluation of UHI mitigation measures, the potential of both numerical (simulation-based) applications and empirically-based urban microclimate models are explored.

Building and Environment, 2010

Annual Review of Environment and Resources, 2015

Urban heat island (UHI) manifests as the temperature rise in built-up urban areas relative to the surrounding rural countryside, largely because of the relatively greater proportion of incident solar energy that is absorbed and stored by man-made materials. The direct impact of UHI can be significant on both daytime and night-time temperatures, and the indirect impacts include increased air conditioning loads, deteriorated air and water quality, reduced pavement lifetimes, and exacerbated heat waves. Modifying the thermal properties and emissivity of roofs and paved surfaces and increasing the vegetated area within the city are potential mitigation strategies. A quantitative comparison of their efficacies and costs suggests that so-called cool roofs are likely the most cost-effective UHI mitigation strategy. However, additional research is needed on how to modify surface emissivities and dynamically control surface and material properties, as well as on the health and socioeconomic ...

Summary.The city of Caracas, as many others Latin-American cities, has experimented a fast growth in the late 20 years, demographic pressures, and the lack of an appropriate urban planification, and others socio-economic problems, tend to reinforce the urbanization phenomena, that has transformed the environment, and the quality of life in these cities. Geospatial tools has provide an interesting perspective to understand the dynamics of these phenomena, the use of thermal band to measure the extension an intensity of urban heat island has been used combined with terrestrial observations, to explain the changes in the urban surface patterns. Combining radiometric, resampling and geometrics corrections techniques, and integrating this information into a GIS, it is possible to compare urban land use to urban surface temperature and identified urban heat critical areas, more accuracy. These works shows the result of the observations develops in the city of Caracas. The geospatial analysis was developed, using LANDSAT 8 OLI images for the period of selected, ERDAS 2014 for image processing, and ARC-GIS 10.3 for cartographic development. Radiometric and Geometric correction (pixel by pixel) with ERDAS, allow us to work at urban scales, in order to observe the variations in the urban canopy related to the urban surface temperatures patterns. Results of the study were useful to identify critical areas and urban structures related to these thermal patterns. This information will be use by urban planners, to develop mitigations and adaptation strategies, in order to prevent the intensification of the urban heat island, during the occurrence of an strong dry season, or heat waves, which might affect the city, the populations and the environment. Key words: GIS, urban heat patterns, adaptation-mitigation strategies.

Advanced Information Systems

The article is dedicated to the methods developed to calculate the main parameters of “heat islands” that appear in densely built-up urban area. Although remote sensing imaging is ideally used to track and detect frequent land cover changes in urban and surrounding areas as a result of sustainable urbanization and to calculate key parameters of "heat islands" seen in densely populated urban areas, satellite imagery is digitally manually The transformation of a parametric image into a land cover map using existing methods of classification is a long process, and therefore methods are proposed to determine the main indicators of the impact of "heat islands" in urban areas. A modified building density index has been formulated, which is highly informative, involving: (a) the proposed index reaches an extremum when the known building density index BDI and NDVI are equalized, (b) when the specified maximum is reached, it is easy to calculate the LST indicator using th...

Eos, Transactions American Geophysical Union, 2005