Review and Critical Analysis of International UHI Studies

seasons, climate types, etc. Further research is therefore required to develop a framework that
will underpin a set of fundamental characteristics that will allow simple analysis and conclusions
to be drawn on the temperature reduction benefits on other buildings/cities in other regions and
climate types.
Despite comprehensive coverage of the effects that trees and vegetation have on energy use, peak
power and CO2 emissions, only energy use for green roofs was given decent coverage. Such
research issues are fundamental and require further investigation for green roofs in particular.
Naturally, the studies examining these issues were case specific, and in the case of urban trees
and vegetation further research is required to understand and quantify the effect of a complex set
of variables upon the UHI mitigation potential and achieving other environmental goals: tree
cover ratio, tree size, health, type, location, orientation, growth/mortality rates, climatic zones,
etc. It is also important that the benefits of energy efficiency, transfer to low/non‐carbon based
fuels and energy conservation in place of urban green solutions are examined to see their relative
effectiveness in reducing energy use, peak power and CO2 emissions.
Of the studies that examined the costs associated with green roofs some attempted to quantify a
sample of the benefits including: Storm water reduction, air pollution and greenhouse gas effects,
energy cost savings, installation and maintenance costs, etc. All but one study attempted to
incorporate all these factors into their costing models and thus the full range of benefits or
drawbacks of the green roofs were not examined in great depth. No studies reviewed for either
green roofs or trees and vegetation managed to quantify the benefits/costs of aesthetics, use of
green roofs for food production and increased biodiversity. Further research is required to collect
empirical data on all the proposed benefits and their respective economic benefits. Many of the
proposed benefits are highly dependent upon the urban green designs and green roof designs
installed in buildings – therefore their costing is highly case specific. On a similar basis to green
roofs, there was limited research conducted to understand and account for the range of benefits
and costs associated with trees and vegetation. It appears that no attempt was made to provide a
comparison of the benefits and/or costs of green roofs or trees and vegetation over efficiency
measures and other cool technologies. Such estimates could prove critical in understanding
whether urban green areas and green roofs are a practical choice in mitigating the UHI effects for
particular cities.
In summary:
� Future research needs to examine the effectiveness of green roofing and urban green areas
across the full spectrum of climate types both at the micro and macro scales to identify
optimal operating conditions;
� Further field experimentation to collect data and model refinement is required to account
for the complex set of variables presented by the direct and indirect effects of green roofs
and urban trees and vegetation;
� Further research development is required to understand the building specific constraints
associated with green roof implementation;
� Research needs to be conducted into quantifying the peak power and CO2 savings
associated with green roofs;
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