Urban heat island
An urban heat island (UHI) is a metropolitan area which is significantly warmer than its surroundings. As population centres grow in size from village to town to city, they tend to have a corresponding increase in average temperature, which is more often welcome in winter months than in summertime.
The problem is that in the Maldives it’s always summertime, and Male’ (capital) is neither a village nor a town. Male’ is an ever growing Mini Manhattan.
The island of Male’ is heavily urbanized, the city taking up essentially its entire landmass. It is the world's most densely populated city with slightly less than one third of the nation's population living in this less than 2 square km capital city of the Maldives.
Male’ has over time become a concrete oven. At night heat is no longer a joke but a nightmare while still awake.
The principal reason for the night-time warming is (comparatively warm) buildings blocking the view to the (relatively cold) night sky. Materials commonly used in urban areas, such as concrete and asphalt, have significantly different thermal bulk properties. This initiates a change in the energy balance of the urban area, often causing it to reach higher temperatures than its surroundings. The energy balance is also affected by the lack of vegetation and standing water in urban areas. 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. This is called the "canyon effect". Another effect of buildings is the blocking of wind, which also inhibits cooling by convection.
Another consequence of urban heat islands is the increased energy required for air conditioning and refrigeration in cities that are in comparatively hot climates.
Concrete can hold roughly 2000 times as much heat as an equivalent volume of air.
Throughout the daytime, particularly when the skies are free of clouds, urban surfaces are warmed by the absorption of solar radiation. As described above, the surfaces in the urban areas tend to warm faster than those of the surrounding rural areas. By virtue of their high heat capacities, these urban surfaces act as a giant reservoir of heat energy.
At night, however, the absence of solar heating causes the atmospheric convection to decrease, and the urban boundary layer begins to stabilize. If enough stabilization occurs, an inversion layer is formed. This traps the urban air near the surface, and allows it to heat from the still-warm urban surfaces, forming the nighttime air temperature UHI.
The problem is that in the Maldives it’s always summertime, and Male’ (capital) is neither a village nor a town. Male’ is an ever growing Mini Manhattan.The island of Male’ is heavily urbanized, the city taking up essentially its entire landmass. It is the world's most densely populated city with slightly less than one third of the nation's population living in this less than 2 square km capital city of the Maldives.
Male’ has over time become a concrete oven. At night heat is no longer a joke but a nightmare while still awake.
The principal reason for the night-time warming is (comparatively warm) buildings blocking the view to the (relatively cold) night sky. Materials commonly used in urban areas, such as concrete and asphalt, have significantly different thermal bulk properties. This initiates a change in the energy balance of the urban area, often causing it to reach higher temperatures than its surroundings. The energy balance is also affected by the lack of vegetation and standing water in urban areas. 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. This is called the "canyon effect". Another effect of buildings is the blocking of wind, which also inhibits cooling by convection.
Another consequence of urban heat islands is the increased energy required for air conditioning and refrigeration in cities that are in comparatively hot climates.
Concrete can hold roughly 2000 times as much heat as an equivalent volume of air.
Throughout the daytime, particularly when the skies are free of clouds, urban surfaces are warmed by the absorption of solar radiation. As described above, the surfaces in the urban areas tend to warm faster than those of the surrounding rural areas. By virtue of their high heat capacities, these urban surfaces act as a giant reservoir of heat energy.
At night, however, the absence of solar heating causes the atmospheric convection to decrease, and the urban boundary layer begins to stabilize. If enough stabilization occurs, an inversion layer is formed. This traps the urban air near the surface, and allows it to heat from the still-warm urban surfaces, forming the nighttime air temperature UHI.
posted by Muhammadh | 2:46 AM
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