Review and Critical Analysis of International UHI Studies

workday effect and weekends. Studies were undertaken in six large US cities. He found
summertime maxima up to 60 Wm‐2 and winter maxima up to 75 Wm‐2. Limitations in this
study were that using Census as a tool for obtaining population figures does not take into
account those that travel in for work from outside the study area, therefore daytime figures for
population will often be larger [124].
Offerle looked at the surface energy balance of a European City for a two year period, they
estimated anthropogenic heat through residual readings from net heat storage. Results were
maximas of 32 Wm‐2 from October to March and ‐3 Wm‐2 from June to August. Negative value
indicates the underestimation of turbulent fluxes [125].
Simmonds analyses data from the daily values of maximum and minimum temperatures, rainfall
and some pollution data over a 134 year period. They found that the only variations to have
taken place were in the winters of the most recent period 1964‐1990 where maximum and
minimum temperatures were greater on weekdays compared to weekends, rainfall was also
found to be greater on weekdays [126].
Ichinose et al studied energy consumption in central Tokyo over variable land, he used energy
use statistics, land use data and numerical modeling. He found that heat flux exceeded 400 Wm‐2
in daytime, and the maximum value was 1590 Wm‐2 in winter of which 51% was from hot water
supplies. In winter, office energy demand peaked at 9am and reduced throughout the day, hotels
had a larger demand at nighttime and demand in the residential sector had two peaks, at 8am
and 9pm. In the summer daytime space cooling demand was constant but peaked at nighttime in
the residential sector at around 9pm. Ichinose concluded that the near surface temperature in
Tokyo could be reduced by a maximum of 0.5°C if the energy demand for hot water was reduced
by 50% and space cooling by 100% [038].
A Chinese city with a dense population produces 37.87 x 10 Mega Joule daily [137].
2.1.4 Geometric Effects of Urban Design and Sky View Factor
Urban geometry refers to the dimensions and spacing of buildings in a city [078]. Tall buildings
and narrow streets create urban canyons which affect wind speeds, energy absorption and heat
emissivity. Also densely arranged buildings allow only low winds thus heat and air pollutants
aren’t as easily dispersed [157].
Oke discusses urban geometry and its effects on solar radiation and identifies two factors, albedo
and solar access. Building materials with a low albedo will absorb solar radiation and store heat,
solar access means building interiors that are sunlit benefit pedestrians on comfort and
psychological levels [121].
Sky view factor is defined as the ratio of the area occupying the sky view to the whole sky area
[118]. There are a number of ways it can be measured: scale model, analytical method –
estimation by graphics, computer analysis of photography using a fisheye lens, evaluation of GPS
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