Saturday, January 17, 2015

Urban Heat Islands

Urban heat islands is the phenomenon where the urban regions experience elevated temperatures than their rural surroundings. This increase in temperature can vary from 1 to 3 degree Celsius.( 1 million city)
Causes of UHI:
1. Reduced vegetation in urban areas:
Vegetation provides shade, evapotranspiration, moisture, and permeable ground surface which all help in lowering temperatures. But in its, absence, urban areas have higher temperatures.
2. Urban materials
Urban materials, such as roof, paving etc. have lower albedo, higher heat capacity and thermal emmisivity than their rural surroundings, and thus absorb more sunlight thus increasing temperatures.
3. Urban geometry
Urban areas discourage proper wind flow, and thus hampering the cooling effect of wind.
4. Anthropogenic heat: i.e. heat from human activities.
Consequences of UHI:
1. Increased energy consumption.
The increased need for cooling increases consumption
2. Elevated emission of air pollutants and green house gases.
Increased energy demand for cooling needs increases energy production and consequent emission.
3. Compromised human health and comfort.
Due to Heating and increased pollution.
4. Impaired water quality
Surface urban heat degrades water quality.

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