Review and Critical Analysis of International UHI Studies

One US study written in 1998 seeks to identify the barriers that must be overcome in order to
ensure mass market uptake of cool community’s strategies (focus on cool materials, shade trees
and demonstration strategies) [027] – naturally some of these barriers have been overcome to
varying degrees through the evolution and maturing of technology, policy and strategy – some
examples from the literature are presented. For cool roofing/paving materials /shade trees the
following barriers have been identified [027, 053, 060]:
� Rating and Testing: lack of information from manufacturers to the market on the
performance of the products – this yields product differentiation issues for the consumers.
Such issues can be dealt with through the use of industry approved test measures (for the
solar reflectance and thermal emittance) and product labeling and/or information database
– a working example is the Cool Roof Rating Council database;
� Cool Materials in New Builds: No incentive for builders to incorporate cool roofs into new
builds due to no recognition of energy performance merits of cool roofs by the codes – in
the US the American Society for Heating Refrigeration and Air‐conditioning Engineers
(ASHRAE) included credits pertaining to cool roofs;
� Low‐Emitting Trees: trees produce biogenic emissions which are precursors to smog. It is
therefore important that groups looking for mass plantation to mitigate the UHI select the
lowest emitting trees. Research in the US is being conducted to categorize the various
species for their relative merits. A working example in the US is research conducted at the
university level to quantify and catalogue the ozone‐forming potential (OFP) of various
tree species also developed by the USDA Forest Service and integrated in the STRATUM
tree data inventory tool [077]. In the US there have also been significant efforts by
government departments (Department of Energy and Department of Defense) to set‐up
demonstration projects on their facilities to illustrate the potential energy savings
associated with mass strategic shade tree plantation.
� Building Performance Standards (Shade Trees): difficulty in the integration of energy
credits for shade trees despite numerous studies proving their relative energy saving and
smog reducing credentials – thus not providing incentive to building owners and
designers to integrate trees and strategically locate them. It has been suggested that
local/state codes and ordinances could be used to promote planting of shade trees ‐ some
states in the US have sought to implement mass tree planting programs through the State
Implementation Plans (SIPs) to meet clean air standards.
A Japanese study suggests that there needs to be a rapid transition from research to policy
implementation. It highlights that there is a growing need to begin to adopt more long‐term mass
scale implementation measures as the short‐term, small scale measures currently implemented
haven’t necessarily yielded the results hoped for both in terms of performance and in‐terms of
proof of scale. The mass implementation, data collection and demonstration should help
overcome some of these barriers and thus serve as model areas in Japan and rapidly urbanizing
cities throughout Asia [047].
A US study suggests that the future prospects of implementation of UHI mitigation strategies
rely upon: ability to demonstrate synergies with other areas of the urban climate; climate changes
at the global scale – as these often have magnified effects upon the urban environments;
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