Review and Critical Analysis of International UHI Studies

savings are used over solutions that provided just indirect energy savings e.g. pavements. Most
studies indicated that cool roofs and urban tree planting held the key to providing energy,
pollution and temperature reduction benefits and suggested that cool pavements also had a role
to play but due to their indirect nature and lack of data on their performance no accurate
quantification of these indirect benefits were established. There are however, certain shortfalls in
the broader direct/indirect effect analyses that were conducted, these are highlighted below:
� Climate Types: most of the research focus in examining the urban heat island mitigation
potential upon the building energy load has been U.S. centric and at best has typically
covered only a select range of climate types ‐ equatorial, arid and warm temperature
climates. Naturally, the performance and effectiveness of the key UHI countermeasures
(roofs, pavements and urban trees and vegetation) are affected by their regional climate
they operate in. Therefore of the studies that extrapolated results from observations in a
select range of regions do not necessarily yield accurate evaluations of a mass
implementation scale‐up of the national energy savings potential;
� Model/Simulation Calibration: the studies were founded predominantly on small scale
direct/indirect observations and then translated the observed phenomena into models.
There was no mass implementation/experimentation conducted such that the outcomes
could be used to verify and calibrate models at the macro‐scale. This validation process is
critical particularly for the indirect effect countermeasures such as pavements, where the
benefits are difficult to quantify;
� Direct Benefits of Thermochromic Coatings: a study examining the use of thermochromic
pigments to modify the material surface color with temperature indicated that they could
be used to save energy both at winter and summer periods. These were based upon small
scale material tests. Significant research efforts are required to achieve material stability
that will allow the confirmation of such performance characteristics. Therefore the claims
of direct energy performance benefits for both winter and summer periods are
premature;
� Higher Quality Data/Mapping: In the studies which evaluated countermeasure
implementation at city and national scales it was evident that approximations had been
made on the urban city makeup. Although in some cases they did provide respectable
estimates on the roof areas based on building/housing stock data, they did not account
for built structure complexity which would affect the effectiveness of the indirect benefits
associated with countermeasures such as cool pavements (e.g. shadowing, building
materials and sky view factor) – naturally these factors are complex to model but are
critical if scalable estimate are to be established;
� Fundamental Influencing Processes: Before reliable estimates of the energy savings
attributed to mass cool pavement and urban trees planting programs can be established
the studies need to develop their understanding of the basic influencing processes. This
is particularly true of studies examining cool pavements where the radiative and thermal
phenomena of pavements are complex to model – this could lead to the emerging
indirect estimates being inaccurate;
� Building Energy Consumption Factors: Few studies addressed the internal building
parameters that directly impact the energy use and resulting CO2 emissions. These
internal parameters take the form of; occupant energy use, efficiency and control of the
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