HEAT ISLAND EFFECT

HEAT ISLAND EFFECT OF URBAN 

AREAS

 Urban heat island effect?

An urban heat island is the name given to describe the characteristic warmth of both the atmosphere and surfaces in cities (urban areas) compared to their (non-urbanized) surroundings. The heat island is an example of unintentional climate modification when urbanization changes the characteristics of the Earth’s surface and atmosphere.

Causes of Urban Heat Island:

1.Reduced vegetation in urban regions :

Reduces the natural cooling effect from shade and evapotranspiration.

2.Properties of urban materials:

Materials commonly used in urban areas for pavement and roofs, such as concrete and asphalt, have significantly different thermal bulk properties and surface radioactive properties than the surrounding rural areas. This causes a change in the energy balance of the urban area, often leading to higher temperatures than surrounding rural areas.

3.Urban geometry:

The height and spacing of buildings affects the amount of radiation received and emitted by urban infrastructure. The tall buildings within many urban areas provide multiple surfaces for the reflection and absorption of sunlight, increasing the
efficiency with which urban areas are heated.

4.Weather:

Certain conditions, such as clear skies and calm winds, can foster urban heat island formation.

5.Geographic location:

Proximity to large water bodies and mountainous terrain can influence local wind patterns and urban heat island formation.

6.Human Activities :

Air conditioning, manufacturing, transportation, fossil fuel combustion and other human activities discharge heat into urban environments.

7.Pollution :

High levels of pollution in urban areas can also increase the UHI, as many forms of pollution change the radioactive properties of the atmosphere.

Consequences of Urban Heat Islands:

1.Impaired air quality :

Warmer air accelerates the formation of smog (ozone) from airborne pollutants like nitrogen oxides and volatile organic compounds. Elevated demand for cooling energy in the form of Air conditioning and Refrigerator use can also increase the emission of air pollutants and greenhouse gases from fossil-fuel power plants.

2.Impact on Health :

Higher air temperatures and lower air quality can cause heat-related and respiratory illnesses,

3.Effect on Weather :

It may also increase cloudiness and precipitation in the city, as a thermal circulation sets up between the city and surrounding region.

4.Impact on Plants and Forest :

High temperatures may create disturbances on ornamental plants and urban forests.

5.Impact on water bodies :

It may increase temperatures of urban water bodies which lead to a decrease in diversity in the water.

To reduce the effect of urban heat island,there is need to decrease anthropocentric heat emissions through energy efficiency technologies in the building and vehicle sectors.Also there is need to modify vegetative cover and surface properties of urban materials.

Urban heat island is phenomenon in which average temperature of pockets of metropolitan area is higher than that of surrounding towns.

Causes of creation of heat islands are
1) Evapotranspiration rate in the city is lower than that of the villages so heat get trapped and results in elevated temperature.
2) Dry impervious surfaces are high in the cities like pavements, roads etc. That absorb heat in day time but evaporate very slowly.
3)Tall buildings, less trees and type of building materials are also responsible for high temp.
4)Higher industrial pollution as compared to surrounding towns.

Consequences of Urban heat island

1) Impaired water quality.
2) Elevated emission of air pollutants and GHG.
3) Compromised human health.
4) Impaired water Quality.

There are some good consequences also such as increased life cycle of plant in Urban Area and relatively less chilly winter nights but that did not qualify as conciliatory argument.