Characteristics Of Urban Heat Islands

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What is an urban heat island?

Urban Heat Islands (UHI) are a phenomenon where the temperature of the surface and atmosphere of an urban area is higher compared to the surrounding rural areas and suburban areas. It is an illustration of unintentional climate change as a result of urbanization (the process wherein population shift from rural areas to urban areas and the way society changes to accommodate the change). Another name for UHI is “local warming” as opposed to global warming.

Urban Heat Islands are indicated by the regional change in temperature and the time change in temperature, which are measured hour by hour. When measuring the effect of UHI in term of temperature one must compare the temperatures in the cities (urban areas)
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Scientists measure air temperatures for CLHI or BLHI directly using thermometers, whereas the SHI is measured by remote sensors mounted on satellites or aircraft. (JA Voogt, 2004)
Characteristics of urban heat islands

The Overall spatial form (shape) of the heat island
The reason urban heat islands were given there name is because on isothermal charts they looks like an island (due to temperatures being higher than the surrounding areas).

The temperatures of the canopy-layer air make a sharp rise at the boundary of rural- suburban areas. Thereafter the temperatures increase gradually as one gets closer to Central Business district (CBD) (Downtown), where the highest temperatures occur. The boundary layer heat islands less variability the in temperatures than the other urban island types.

Heat island
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The following factors also contribute to the formation of urban heat islands: urbanization, weather(wind speed and cloud cover), geographic location, time of day and season, city form and city functions, population size/density, land and building material( B Offerle, 2006) and Anthropogenic heat sources(cars air conditioning, power plant, etc.) (Qihao Weng, 2004
Urbanization
Urbanization is the main cause for the formation of urban heat islands. As urbanization progresses over time, the temperature of Urban Heat islands also increases. This is as a result of when vegetation is replaced with roads, building, and other infrastructure, to accommodate the growing populations; these surfaces absorb the sun’s rays. This causes the surface and overall temperature to rise.
Lack of vegetation
Vegetation provides a natural cooling effect as shade it provides shade, has moisture trapped within the soil that evaporates, which produces water vapor that contribute to cooling the air and intercepts radiation.

City form and
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