Cause And Causes Of Urban Decentralization
History[ edit ] The phenomenon was first investigated and described by Luke Howard in the s, although he was not the one to name the phenomenon. Between andabout 30 studies were published annually; by Cauuses, that number had increased toand byit was more than A comparison of the images shows that where vegetation is dense, temperatures are lower.
There are several causes of an urban heat island UHI ; for example, dark surfaces absorb significantly more solar radiationwhich causes urban concentrations of roads and buildings to heat more than suburban and rural areas during the day; [1] materials commonly used in urban areas for pavement and roofs, such read more Cause And Causes Of Urban Decentralization and asphalthave significantly different thermal bulk properties including heat capacity and thermal conductivity and surface radiative properties albedo and emissivity than the surrounding rural areas.
This causes a change in the energy budget of the urban area, often leading to higher temperatures than surrounding rural areas. Forest Service found in that cities in Decdntralization United States are losing 36 million trees each year.
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 " urban canyon effect ". Another effect of buildings is the blocking of wind, which also inhibits cooling by convection and prevents pollutants from dissipating. Waste heat from automobiles, air conditioning, industry, and other sources also contributes to the UHI. While temperature difference is significant all year Decentra,ization, the difference is generally bigger in Winter.
These two Decentarlization slightly different diurnal and seasonal variability and have different causes [20] [9] Diurnal behavior[ edit ] Cities often experience stronger urban heat island effects at night; effects can vary with location and topography of metropolitan areas The IPCC stated that "it is well-known that compared to non-urban areas urban heat islands raise night-time temperatures more than daytime temperatures. The air temperature difference between the UHI and the surrounding environment is large at night and small during the day. The opposite is true for skin temperatures of the urban landscape within the UHI. Surfaces in the urban areas tend to warm faster than those of the surrounding rural areas. By virtue of their high heat capacitiesurban surfaces act as a giant reservoir of heat energy. For example, concrete can hold Cause And Causes Of Urban Decentralization 2, times as much heat as an equivalent volume of air.
As a result, the large daytime surface temperature within the UHI is easily seen via thermal remote sensing. It is theorized that, due to the atmospheric mixing that results, the air temperature perturbation within the UHI is generally minimal or nonexistent Aggression In Seaworld the day, though the surface temperatures can reach extremely high Decdntralization.
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The absence of solar heating leads to the decrease of atmospheric convection and the stabilization of urban boundary layer. If enough stabilization occurs, an inversion layer is formed.
This traps urban air near the surface, and keeping surface air warm from the still-warm urban surfaces, resulting in warmer nighttime air temperatures within the UHI. Other than the heat retention properties of urban areas, the nighttime maximum in urban canyons could also be due to the blocking of "sky view" during cooling: surfaces lose heat at night principally by radiation to the comparatively cool sky, and this is blocked by the buildings in an urban area. Radiative cooling is more dominant when wind speed is low and the sky is cloudless, and indeed the UHI is found to be largest at night in these conditions.]
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