8/9/2019 Climate Study and the Urban Heat Island

1/3

The Urban Heat Island

Urban regions are among the most quickly changing environments on Earth. As cities

grow, they impact local and regional climates, including temperature averages andextremes. Urban areas are known to change mean yearly air temperatures by 0.2-2.4*C

per 100 years and up to 10*C by night. Temperature changes affect urban settler in manyways, influencing their energy costs, water availability and quality, recreation, health and

comfort, ecological services, air quality and visibility levels, and overall quality of life.

The climate section of the UHI initiative is about Analyzing Local and Regional Climate

Changes: Past, Present-Day, and Prospects for the Future. In addition to analyzing

temperature data - analysis of the circumstances surrounding historical and present daycollection sites (location, area characteristics) is key for accurate and good experiments.

Example of typical urban effects on the local climate system;

Background - What is the Urban Heat Island (UHI)?

There are three types of heat islands:

canopy layer heat island (CLHI)

boundary layer heat island (BLHI)

surface heat island (SHI)

Of which type CLHI is the most common.

8/9/2019 Climate Study and the Urban Heat Island

2/3

For nearly 100 years, it has been believed that urban areas affect the local climate, mainly

in terms of the temperature. The urban effect is due to changes in the thermal

compositions, moisture and aerodynamic character of the built-up environment. These

changes create a distinct urban boundary layer, or heat dome. This heat dome extendsvertically above the city, and in windy conditions can be located downwind as a plume.

The temperatures within the heat dome can be 6*C higher than the surrounding areas.

At a given time of day, a balance of incoming energy from the sun and outgoing heatfrom the surface determines the surface temperature. Solar radiation strikes the surface,

and reflects a portion back to space and with the remainder both heating the surface and

evaporating any water that may be present. The heat is transferred upwards, in part bythermal (infrared) radiation and by turbulence due to the wind flowing over the surface.

In built urban areas, there is generally less water on the surface, as compared to the

outlying rural areas. In addition, the walls of buildings reflect heat horizontally insteadof vertically, trapping heat around the building or ground level. Both of these factorsresult in the increase of temperature that results in an urban heat island. Basically, this

Heat Island effect occurs when not much light and heat is reflected back to space.

The low level heating over the cities also has low pressure associated with it. This results

in a flow from the rural areas toward the urban center, with the air converging and risingover the city. This rising air can, if conditions are favorable, result in the triggering of

thunderstorms over the cities and these can escalate into bigger and worrier cases.

An example:

8/9/2019 Climate Study and the Urban Heat Island

3/3

Another example:

Consequences and conclusion

The higher temperatures within the urban dome can also increase the rate of some

chemical reactions, such as formation of ground-level ozone. As a result, the urban heatisland can have a profound effect on human comfort and health.

The consequences of urban heat islands are thermal discomfort whereby the amount of

heat received into the body is over the bodily-capable standards, increased rates of

formation of key air pollutants, increased health risks, increased air conditioning energyusage, additional investments in generating higher amounts of electricity and extreme

degradation of materials.

Therefore, to curb such occurrences from happening, we should translate research results

into effective countermeasures; Specifications and test procedures for products, building

codes and manufacturing standards and financial incentives are certain policies tried outin the world successfully today.

It is easy to be intimidated by the scale of action needed to implement effective

countermeasures. However, cities are constantly renewing themselves and there are manyexamples of transformations of the urban fabric, including street lighting, mosquito

abatement, and fuel switching. These transformations can occur surprisingly quickly whenthe benefits are clear. Thus, the challenge is to find countermeasures with modest costs and

clear benefits. is from www.iea.org/Textbase/work/2006/heat/meier_global_view.pdf