What Is Urban Heat Island Effect & How to Reduce It?

As soon as people started to build huge houses and big and small cities were created, the term “heat island” appeared. It is used to describe the areas, which are created around rural areas and are hotter. “The annual mean air temperature of a city with 1 million people or more can be 1.8–5.4°F (1–3°C) warmer than its surroundings. In the evening, the difference can be as high as 22°F (12°C).” (Voogt 2002). This is evident that heat islands have serious effects upon communities, because they bring the increase of peak energy demand in summer time, the costs for aid conditioning are much higher, greenhouse effect and air pollution are also the direct results of heat islands influences. All these factors are critical for increase of cases of heart illnesses by individuals, general mortality level and poor quality of waters in the regions. The issues of heat island are studied nowadays with great attention in order to work out the way of reducing their effects upon humans and natural environments.

The roots of the heat island effect is related to roofs and pavements surfaces, which became extremely hot in summer days, if these surfaces are under the direct impact of sun rays. Shaded surfaces are closer to the air temperatures. This is the main reason, why the temperature in urban areas is higher, than in neighboring regions, where there are not so many buildings and pavements. Along with development of the cities most of the vegetation is lost and most of the surface becomes covered with pavements and buildings. Such changes of ground cover lead to the fact that there is no shade enough and no moisture in order to make the urban areas cooler. “Built-up areas also evaporate less water, which contributes to elevated surface and air temperatures. Properties of urban materials, in particular solar reflectance, thermal emissivity, and heat capacity, also influence the development of urban heat islands, as they determine how the sun’s energy is reflected, emitted, and absorbed.” (Voogt 2002).

All humans are closely related to nature and the environments, they live in, and thus the impacts of heat islands are dangerous first of all to people themselves. Too high temperatures especially during summer time could have effects upon the environment and general life quality for humans. Positive effects are few, for example increased temperatures contribute to lengthening of the plant growing season. Still most of these impacts are rather negative, like for example:

  • increase of energy consumption
  • increase of the amount or air pollution and strengthening of greenhouse effect
  • negative impacts upon human health
  • worsening of the water quality.

“As shown in the example from New Orleans, electrical load can increase steadily once temperatures begin to exceed about 68–77°F (20–25°C). Other areas of the country show similar demand curves as temperature increases.” (Akbari 2005). Increased energy consumption could be explained by the fact that elevation of the temperatures in the cities forces people consume more energy for cooling. “Research shows that electricity demand for cooling increases 1.5–2.0% for every 1°F (0.6°C) increase in air temperatures, starting from 68 to 77°F (20 to 25°C), suggesting that 5–10% of community-wide demand for electricity is used to compensate for the heat island effect.” (James 2002). Especially the situation is tough in summer afternoons. There is a need to work out additional systems of control in order to avoid the situations of power outages. The increase of energy consumption is related to another negative effect, namely to the fact that those companies, which supply electricity, usually work with fossil fuel plants in order to correspond to the increased demands. This in its turn leads to increase of the air pollution and green house emissions. “The primary pollutants from power plants include:

  • sulfur dioxide (SO2)
  • nitrogen oxides (NOx)
  • particulate matter (PM)
  •  carbon monoxide (CO) and mercury (Hg).” (James 2002).

China is the country, which could be currently characterized by the high level of technological development and urbanization. Most of the cities is China suffer from unprecedented levels of aerosol pollution. “The warming rate ranging from 0.108 to 0.483 °C/decade for average air temperature is generally consistent with the warming trend of other urban regions in China and in other urban agglomerations worldwide.” (Akbari 2005). On the basis of the satellite observations, the experts managed to show that urban haze pollution is the source of the intensification of UHI in China during night time. “In the analysis, the surface UHI intensity ΔT is the difference in surface temperature between the urban and the adjacent rural land3, and haze pollution is measured by the aerosol optical depth (AOD). We then use an urban climate model in conjunction with an observation minus reanalysis (OMR) method for aerosol longwave radiation enhancement, to quantify the haze contribution to the surface UHI intensity in three climate zones (humid, semi-humid and semi-arid) across China.” (Akbari 2005). This happens because of the increase of the longwave radiation. Semi-arid cities suffer more from the warming effect in comparison to semi-humid or humid climates. According to the research data those aerosols, which are the reasons of haze pollution, are made of the finest particles, present in gas. The result of this process is formation of haze, which is still not studied properly. Current studied aim at finding the ways of taking care of health problems of people, living in these areas, for example coping with such problems as heat stress of heatstroke.

Modern scientific findings also consider geographical variations. Before the experts, studying North American countries, assumed that the reason of the differences between the temperatures of rural and urban areas could be explained by the presence of such biophysical factors as heat convection efficiency. To some extent Chinese cities turned out to be similar, because the size of the country is also huge and there are different climate zones in it. At the same time some of the Chinese cities did not correspond to the model of the North American region. “In North American cities, larger population was linked to more severe UHI, but in China, city size did not correlate to UHI severity. Another contrast the researchers found was that while North American cities suffered from more serious UHI in the daytime, in China, the phenomenon was more pronounced during the nighttime.” (Akbari 2005).

The major aim of the scientists is nowadays to find the way to reduce the haze pollutions in Chinese cities. This strategy is expected to cope with the negative results of the increased urban temperatures in China. For the future there is also an important task of creating climate models, which would provide the opportunity to control the nighttime urban heat island effect. Most of the researchers do not have any commonly accepted idea about the effect of haze and aerosol pollution upon the whole climate system. There is still place for investigation, as apart of theoretical predictions, it is necessary also to have experimental data.

Overall, urban climatologists have made the attempts to study urban heat islands for a relatively long period of time already, still the community concerns about this matter are more recent. Nowadays a lot of attention is paid to the problem of urban heat island effect. It is evident that there is a growing need to conduct further research of the reasons of this process and its effects and work out the strategies for heat island reduction. At the moment there are already the projects of green roofs, cool roofs, cool pavements, etc. worked out.

Works cited:

Akbari, H.  Energy Saving Potentials and Air Quality Benefits of Urban Heat Island Miti- gation, 2005

James, W. Green roads: research into permeable pavers. Stormwater, 2002, 3(2):48-40

Kalkstein, L.S. A New Approach to Evaluate  the  Impact  of Climate  upon Human Mortality. Environmental Health  Perspectives, 1991

Oke, T.R.   Urban  Climates  and  Global  Environmental Change. Applied  Climatology:   Principles & Practices.  New York, NY:  Routledge, 1997

Voogt, J. Urban  Heat  Island.  Encyclopedia of Global  Environmental Change,  Vol. 3.  Chichester: John Wiley and Sons, 2002

The terms offer and acceptance. (2016, May 17). Retrieved from

[Accessed: March 28, 2024]

"The terms offer and acceptance." freeessays.club, 17 May 2016.

[Accessed: March 28, 2024]

freeessays.club (2016) The terms offer and acceptance [Online].
Available at:

[Accessed: March 28, 2024]

"The terms offer and acceptance." freeessays.club, 17 May 2016

[Accessed: March 28, 2024]

"The terms offer and acceptance." freeessays.club, 17 May 2016

[Accessed: March 28, 2024]

"The terms offer and acceptance." freeessays.club, 17 May 2016

[Accessed: March 28, 2024]

"The terms offer and acceptance." freeessays.club, 17 May 2016

[Accessed: March 28, 2024]
close
Haven't found the right essay?
Get an expert to write you the one you need!
print

Professional writers and researchers

quotes

Sources and citation are provided

clock

3 hour delivery

person