Review and Critical Analysis of International UHI Studies

The second report recognized that changes in urban land use has an impact on urban heat island
intensity (UHII) and subsequently increases temperatures in urban areas up to 4.7°C compared to
rural areas. It also made a strong correlation between urban development and air temperature
[137].
A study in the USA compared temperature readings from 1219 weather stations across the
country over a period of 83 years. The results were that urban effects on climate were detectable
even in small towns. A mean annual temperature increase was recorded at 0.1°C compared to
rural stations with smaller populations. The study found that urbanization decreases daily
maxima in all seasons except winter and the temperature range in all seasons also decreased. An
increase was identified in the diurnal minima and daily means in all seasons. The results of this
study are objectionable as 85% of the stations used were in areas where population was less than
25,000 inhabitants [147].
In the studies on land use and surface temperatures the following research methods were used:
Landsat Thematic Mapper images, topographical maps, vegetation maps, aerial photographs,
satellite images and climatic data. Results showed that changes in land use and land cover
widens the temperature difference between urban and rural areas. Vegetative cover eased
temperatures in urban areas but warmed land in colder weather. Of all the land use types studied
urban and built‐up areas showed the highest average temperatures [138].
Some limitations to the use of temperature records in cities is that some cities don’t keep records
at all, records are generally only for the last 100 years, temperature recording devices are not best
placed and are sometimes in rural areas outside of the city, devices are moved from location to
location so constant and consistent measurements are unavailable and finally some cities do not
record summertime temperatures [157].
2.2.2 Air Quality
Cities are often associated with poor air quality and air pollution which result in problems such
as acid rain and smog, a combination of nitrous oxides and suspended particles emitted by
vehicles and factories. As energy demand in urban areas rise, emissions rise exponentially,
which means air pollutants such as carbon dioxide CO2, sulphur dioxide SO2, nitrogen oxide
NOx, carbon monoxide CO and particulate matter PM are released into the atmosphere causing
the aforementioned problems to humans.
The higher temperatures found in UHIs, as discussed in 1.2.1.1, speeds up the chemical reaction
that leads to pollutants such as ozone formation. Ozone is a result of nitrogen oxide reacting with
volatile organic compounds in sunlight and at surface level, is a harmful pollutant [078]. It was
calculated that for every 1°F rise in temperature polluted days may increase by 10% [157]. It is
however, not just air temperature that affects air pollution, other contributing factors include the
air’s dew point, air pressure, cloud cover and wind speed [157].
Six papers were studied on air pollution in urban areas, of these papers one reported results from
China, one from France, two from Taiwan, one from Tanzania and one from Japan. The papers
looked at the association between urban land surface cover, climatic parameters/urban heat
islands and air pollution [136, 139, 140, 135, 014]. One paper also studied pollutants and their
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