Review and Critical Analysis of International UHI Studies

and heat capacity [078]. Solar reflectance or albedo is generally low in urban materials so they
reflect less and absorb more energy thus increasing temperatures at surface level. Thermal
emittance describes the process of how materials release heat back into the atmosphere, generally
more common buildings materials have high emittance values meaning they release heat quickly
and stay cooler. Heat capacity, common building materials such as tar, asphalt, brick and
concrete [001] store solar energy during the day and release it at night, so UHI intensity is often
reported to be stronger at nighttime [098, 078, 014, 139].
In a study by Asaeda surface level heat flux was measured for a number of different materials,
the study found that asphalt had much higher levels of heat capacity and thermal emissivity than
concrete and soil. Asphalt emitted an additional 150 Wm ‐2 in infrared radiation and 200 Wm ‐2 in
sensible transport to the results for bare soil [127].
There is an inverse relationship between latent heat flux and increased vegetation cover. Offerle
et al studied turbulent heat flux in Lodz, Poland by measuring turbulent fluxes, radiative flux,
temperature and humidity, water vapor flux, carbon dioxide and net radiation. They also found
that sensible heat flux was positively related to impermeable land cover and building density.
Offerle’s work could be applied to other cities, but vegetation type should be considered as some
species are non‐transpiring [043].
The roughness of the building material is often commented upon in papers and experts agree that
roughness of building materials means they are more thermally conductive, one study also
showed that the correlation between roughness and air temperatures was stronger during the
night than the day time [116].
Alonso et al studied the UHI of Salamanca, Spain, as part of their study they considered the
intensity of a nocturnal heat island in relation to the surface material. They used a grid system
around the temperature apparatus based on the size of the city and categorized the surface into
percentages of asphalt, buildings, water and green areas. They found that maxima temperatures
were recorded over areas with a higher percentage of urbanization/building cover, the opposite
was found for areas with a higher percentage of green cover [023].
2.1.3 Anthropogenic Heat Sources
Anthropogenic heat is described as heat that is generated from stationary or mobile sources in an
area, in most studies this relates to air conditioning, industrial processes, power plants, buildings,
vehicles and people [007]. Anthropogenic heat is usually measured in Wm‐2 and many papers
have been produced on this study. Five papers were examined and were undertaken in North
America, Asia, Europe and Australia, all studies were in warm temperate climates, however, the
results of the studies differ. Generally values are higher in the winter season in colder climates as
heating loads are heavier.
Sailor splits his findings into three components, building sector, transportation sector and
metabolism based on population density, profiles were developed to take into account the
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