Review and Critical Analysis of International UHI Studies

5 CRITICAL REVIEW OF UHI COUNTERMEASURES
5.1 Introduction
The earlier sections of this study looked to report and review all the seminal research conducted
in the urban heat island space and examine their mitigating potential. In this section, we
undertake a critical analysis of the studies and the opportunities for scale‐up efforts leading from
local to national and national to international efforts.
This analysis begins by examining the two principal methods that were addressed by the papers
to reduce the ambient temperatures and building surface temperatures resulting in lower space
conditioning requirements. This is followed by a critical review of the policy actions for each of
the key mitigating technologies (cool roofs/pavements, green roofs and urban green areas) that
highlights the current status across the globe, the identified barriers to scale‐up, the reach and
level of implementation of these policies and a conclusion presenting a forward path. An
economic review/analysis follows that seeks to identify the climates where the energy savings
alone justify the mitigation efforts and where incentive schemes may be required to justify their
implementation. This is followed with a high level analysis of the barriers and catalysts that may
hinder the mass adoption of urban heat island strategies and technologies and their rate of
deployment. This section concludes by examining the urban planning issues and the degree to
which current practice across the globe may inhibit or facilitate the deployment of the urban heat
island countermeasures.
5.2 Critique of Negative Radiative Forcing Studies
5.2.1 Review of Negative Radiative Forcing and Direct/Indirect Effect Studies
UHI countermeasures mitigate global warming impacts in two principal ways: by lowering
ambient and building surface temperatures, which in turn can reduce the amount of energy
required for space conditioning and the associated energy‐related CO2 emissions, or by
increasing the overall albedo of the Earth’s surface which causes less solar radiation to be
converted into heat in the Earth’s troposphere. This review presents a critique of the two
different classes of studies that have been conducted to date. It is apparent that the first class of
studies are where the large majority of research has been focused and has examined the effects of
increasing the albedo of roofs and pavements and the use of green roofs and urban green areas to
both directly and indirectly reduce urban temperatures and building/city energy use and
consequently CO2 emissions. The second class examines how the increase in the urban albedo
induces a negative radiative forcing effect on the Earth and equates this to CO2 emission offsets.
Interestingly, the literature suggests that the magnitude of mitigation potential delivered via the
negative radiative forcing effect might be much greater than the mitigation potential from
reduced space conditioning energy use; however, perhaps because the former brings no direct
economic benefits to the end‐users it has been much less thoroughly researched.
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