Review and Critical Analysis of International UHI Studies

Some UHI impacts are positive such as increased growing seasons for plants, but most are
negative. Increased air temperatures can cause or exacerbate poor air and water quality, impaired
health and psychological conditions, increased energy consumption and negative impacts on the
economy such as agricultural losses, impacts to tourism and financial losses due to increased
extreme weather events [078].
The following papers review the literature found in this area, the papers are categorized into
impacts on: temperature; air quality; energy use; peak power; CO2 emissions; health; and the
economy.
2.2.1 Temperature Increase
The urban heat island effect is quantified by rises in air and surface temperatures in urban areas
compared to the surrounding rural areas. Increased temperatures make city living more
uncomfortable and when nighttime temperatures rise it can affect or even inhibit sleep. High
temperatures in extreme circumstances such as heat waves can cause death. Rising temperatures
boost energy consumption due to the demand for cooling appliances such as air conditioning
units and fans [078]. Temperature increases are also linked to increased rainfall and the
production of photochemical oxidants [047]. Urban heat islands follow a similar temperature
pattern from city to city, with a few exceptions. Starting from rural areas temperatures start to
rise at the edge of the city and continue to rise until they reach their peak over the city centre,
where buildings are most dense. Pockets of cooler air are often found over parks or woodland
[157].
Air and surface temperatures in urban areas are affected by many different variables,
topography, the features of an area, the climate type of the region and temporary conditions like
weather patterns and breezes. Breezes can negate the urban heat island effect by the mixing of
cooler winds with the warmer city winds thus creating an overall cooling effect [157].
There are 11 papers addressing air temperature changes in urban climates. Of those 11 studies
three are from China, three from Japan, one from Singapore, one from Hong Kong, two from the
USA and one from the UK.
Studies in Tokyo have recorded the total number of hours where air temperature was more than
30°C in a typical summer has doubled in the last 20 years [148].
The papers measured urban growth on surface temperature [145, 137, 147] and land use on
surface temperature [138, 144, 096].
For the impact of urban growth on surface temperature various research methods were used:
remote sensing, Landsat, GIS modeling and data from weather stations. In a study in China
results showed uneven growth, an increase of 13.01 Kelvin. The study found that the spatial
pattern of radiant temperatures correlated with urban expansion [145]. This particular study
however failed to take into consideration the land surface type/ roughness and emissivity which
can have a significant impact on temperature readings.
Review and Critical Analysis of International UHI Studies
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