Local Climate Change and Urban Heat Island Mitigation Techniques – the State of the Art (original) (raw)
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Energy Systems, 2013
The most apparent impact of urban development on the environment is the rearrangement of its biophysical attributes. By altering the nature of the surface and generating large amounts of heat, urbanized areas modify the microclimate and air quality. The urban heat island phenomenon, which serves as a trap for atmospheric pollutants, deteriorates the quality of life and has a socio-economic impact in the urbanised areas, has been a research subject at least for the last 100 years.
Three decades of urban heat islands and mitigation technologies research
Energy and Buildings, 2016
Although the urban heat island (UHI) phenomena phenomenon has was been documented over a century ago, the effect of the urban heat island on urban climate and environment during the summer have only been the focus of research over the last three decades. One main characteristics of the recent research has been to evaluate the summertime effects of UHI on energy use, air pollution, outdoor ambient temperature, and citizen health. The second aspect of the recent research has been the development and evaluation of materials to counter the effects of summertime UHI. This paper provides a selective representation (by topic) review of the research on the development and evaluation of mitigation measures, including: cool roofs, cool pavements, and urban vegetation.
MITIGATING URBAN HEAT ISLAND EFFECT BY URBAN DESIGN: FORMS AND MATERIALS
This paper provides a synthesis of three complementary research works that contribute to the same objective: proposing solutions to reduce building energy consumption by modifying local climate. The first work explores urban forms: it proposes methods to describe them and analyze the climatic performances of classified urban forms. The second one focuses on one parameter of direct relevance to urban heat island phenomenon: the surface albedo. The albedo of a city or a district depends on surfaces' arrangement, materials used for roofs, paving, coatings, etc., and solar position. The third one proposes a simulation tool that permits to evaluate the impact outdoor urban environment on buildings' energy consumption. This analysis permits us to propose morphology indicators to compare the relative efficiencies of different typologies. The conclusion discusses the relevance of using indicators (based on physics or morphology, related to site or to built form) in urban design process and proposes a methodology to produce indicators.
Renewable and Sustainable Energy Reviews, 47, 830-843, 2015
Studies on urban heat island (UHI) have been more than a century after the phenomenon was first discovered in the early 1800s. UHI emerges as the source of many urban environmental problems and exacerbates the living environment in cities. Under the challenges of increasing urbanization and future climate changes, there is a pressing need for sustainable adaptation/mitigation strategies for UHI effects, one popular option being the use of reflective materials. While it is introduced as an effective method to reduce temperature and energy consumption in cities, its impacts on environmental sustainability and large-scale non-local effect are inadequately explored. This paper provides a synthetic overview of potential environmental impacts of reflective materials at a variety of scales, ranging from energy load on a single building to regional hydroclimate. The review shows that mitigation potential of reflective materials depends on a set of factors, including building characteristics, urban environment, meteor- ological and geographical conditions, to name a few. Precaution needs to be exercised by city planners and policy makers for large-scale deployment of reflective materials before their environmental impacts, especially on regional hydroclimates, are better understood. In general, it is recommended that optimal strategy for UHI needs to be determined on a city-by-city basis, rather than adopting a “one-solution- fits-all” strategy.
Urban Heat Island: Causes, Effects and Mitigation Measures -A Review
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.
On the use of cool materials as a heat island mitigation strategy
Journal of Applied …, 2008
The mitigation of the heat island effect can be achieved by the use of cool materials that are characterized by high solar reflectance and infrared emittance values. Several types of cool materials have been tested and their optical and thermal properties reveal that these materials can be classified as "cool" with the ability to maintain lower surface temperatures. Cool materials can be used on buildings and other surfaces of the urban environment. Based on these results, a modeling study was undertaken to assess the urban heat island effect over Athens, Greece, a densely populated city, by trying to analyze the impacts of large-scale increases in surface albedo on ambient temperature. Numerical simulations were performed by the "urbanized" version of the nonhydrostatic fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5, version 3-6-1). Two scenarios of modified albedo were studied: a moderate and an extreme increase in albedo scenario. It was found that large-scale increases in albedo could lower ambient air temperatures by 2°C. Furthermore, the impact of high albedo measures on heat island magnitude was estimated by creating a spatial representation of the urban heat island effect over the modeled area. The results of this study can help to promote the adoption of high albedo measures in building energy codes and urban planning regulations.
Practical issues for using solar-reflective materials to mitigate urban heat islands
Atmospheric Environment, 1998
Solar-reflective or high-albedo,* alternatives to traditionally absorptive urban surfaces such as rooftops and roadways can reduce cooling energy use and improve urban air quality at almost no cost. This paper presents information to support programs that mitigate urban heat islands with solar-reflective surfaces: estimates of the achievable increase in albedo for a variety of surfaces, issues related to the selection of materials and costs and benefits of using them. As an example, we present data for Sacramento, California. In Sacramento, we estimate that 20% of the 96 square mile area is dark roofing and 10% is dark pavement. Based on the change in albedo that is achievable for these surfaces, the overall albedo of Sacramento could be increased by 18%, a change that would produce significant energy savings and increase comfort within the city. Roofing market data indicate which roofing materials should be targeted for incentive programs. In 1995, asphalt shingle was used for over 65% of residential roofing area in the U.S. and 6% of commercial. Built-up roofing was used for about 5% of residential roofing and about 30% of commercial roofing. Single-ply membranes covered about 9% of the residential roofing area and over 30% of the commercial area. White, solar-reflective alternatives are presently available for these roofing materials but a low:first-cost, solar-reflective alternative to asphalt shingles is needed to capture the sloped-roof market. Since incoming solar radiation has a large non-visible component, solar-reflective materials can also be produced in a variety of colors. :~ 1997 Elsevier Science Ltd.
Mitigating Urban Heat Island Through Green Roofs
One of the key measures to fight urban heat island (UHI) phenomenon is by increasing the use of green approaches including green technologies and vegetation. However, there is a shortage of available space for establishing greening elements due to high density of urban development and high cost of urban land. By using green roofs, the hottest spots of a city can be mitigated. Further advantages of green roofs include mitigating air pollution, improving management of run-off water, improving public health and enhancing the aesthetic value of the urban environment. This paper reviewed, analyzed, and discussed previous literature on green roofs and their role in alleviating UHI. Previous researches acknowledged the ability of green roofs in UHI mitigation. This paper recommends using green roofs as a main strategy for decreasing the harmful impacts of UHI especially the high air temperatures as well as their ability to add to the greening of cities.