Review and Critical Analysis of International UHI Studies

data. It concluded that dense shade on all surfaces reduced peak cooling loads by 31‐49% and
therefore in hot climates high branching shade trees and low ground covers should be used to
promote both shade and wind. This study however, makes several simplifying assumptions
within both the simulation model (e.g. constant exterior film coefficients, reduced weather data)
and in the input data [039]. Further research is required in isolating the contributing factors to the
peak cooling load and in obtaining an understanding of the mass implementation and scale up
issues associated with landscape design on the peak energy demand.
Two Japanese studies [031, 111] look to establish a comprehensive methodology for the
assessment of UHI countermeasures while including the impact of these countermeasures upon
urban energy demands. This study uses a composite numerical simulation system to express the
city‐block scale interactions between the outdoor weather and the cooling energy demands of the
buildings during the summer. These studies make use of a mesoscale meteorological model
which is fed by an urban canopy model and at the highest detail by a building energy analysis
model. Using this system the study suggests that in large Asian tropical or subtropical cities
where anthropogenic energy demand is concentrated, the UHI effects cause the increase in
building demand to increase by an estimated sensitivity of 3%/degree K in Greater Tokyo,
therefore about 1.6GW of additional demand is required as the regional air temperature increases
by 1 degree K [031, 111]. This therefore examines the interaction between the urban thermal
environment and cooling energy use and peak demand on a city scale using a multi‐scale
simulation. These outcomes have been verified to some degree by data from the field but such
models vary from region/climate and are a composition of several complex and highly targeted
models aren’t applicable at larger scales without the loss of confidence in the results.
Similar such studies have evolved from the US by LBNL and have found and noted in three of
their studies that the peak urban electric demand rises by 2‐4% for each 1K rise in the daily
maximum temperature above the threshold of 15‐20°C. Therefore they conclude and quote that
the additional A/C use caused by this urban temperature increase is responsible for 5‐10%
increase of urban peak electric demand [028, 070, 112].
The remaining studies that examine peak power take similar approaches to the ones described
and consequently suffer from the same short‐falls.
Only four studies addressed the CO2 emissions due to the mitigation of the Urban Heat Island
effect [035, 041, 066, 142]. One study as illustrated that follows examines the effects on CO2 at a
micro‐scale and city scales [041, 066] but other two look to expand their findings to the national
or even global scales [035, 142].
This micro‐scale study conducts a computer simulation at a micro‐individual building scale to
quantify the effects of mass modification to the existing vegetation on the indirect reduction and
atmospheric carbon for two residential neighborhoods in north‐west Chicago. It found the effects
of shading, evapotranspiration and wind speed reduction decreased the total annual reduction of
carbon emissions by 3.2‐3.9% per year for block (a) examined (33% tree cover) and ‐0.2 ‐3.8% in
block (b) (11% tree cover) thus resulting in a total annual reduction averaging 158.7 (+/‐ 12.8) kg
per residence in block (a) and 18.1 (+/‐ 5.4) kg per residence in block (b). This allowed the study to
examine micro phenomena (e.g. the effects of shading and wind speed) on the annual carbon
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