Review and Critical Analysis of International UHI Studies

enefits are complex to measure directly. Further research is required to collect data on cool
pavements and to identify methods of isolating and quantifying the benefits.
Eleven studies examined the temperature reduction capabilities ode to increasing the albedo of
the pavements [026, 035, 066, 067, 070, 073, 079, 112, 127, 128]. The studies broadly confirmed that
increasing the pavement albedo would decrease the pavement temperature. LBNL data quoted
indicated that increasing the pavement albedo by 0.25 would reduce the pavement surface
temperature by up to 10K [070, 112]. Other LBNL estimates have shown that if pavement
reflectance throughout a city was increase from 10% to 35% the air temperature could be reduced
by 0.6k [128]. One study stated that atmospheric models demonstrated that most of the infrared
radiation from the pavement was absorbed within 200m of the lower atmosphere – thus affecting
the near ground temperature [127]. Two studies study ran a simulations for Los Angeles
California and examined the aggregated effect of resurfacing increasing the albedo ‐ one of these
studies looked to replace 2/3rds of the reflective surfaces (pavements and roofs) and planting
three trees per house and the other to increase the average albedo in downtown LA by 0.08
during the summertime and in the Californian south coast air basin by 0.13 – results showed
temperature across LA could be reduced on average between 1.5‐3K and the south basin of
California by 2K [026, 112]. All these studies were conducted for US cities under controlled
models and simulations and therefore require further investigation for a range of different
climates. One study tested the solar spectral properties of five colored thin layer asphalt samples
against traditional black asphalt. Results showed that the colored asphalt had higher levels of
solar reflectance, and lower surface and air temperatures, by as much as 12°C. The researchers
used a range of field measurements and Computational Fluid Dynamics simulation [237]. Only
one study tried to isolate and quantitatively assess the effects of paved surface on the near surface
atmospheric model – critical to understand what factors affect atmospheric temperature [127].
There needs to be a focus on trying to quantify the cool pavement effects on temperature in
isolation to the other mitigation measures. Moreover, pavement temperatures are affected by
both radiative and thermal characteristics ‐ these are complex to model but are essential if
estimates are to be accurate.
Ten papers examined other cool pavement designs (i.e. apart from just altering the albedo) taking
advantage of the effects of factors such as permeable surfaces which retain water and allow
evapotranspiration [047, 067, 068, 073, 127, 128, 134, 228, 229]. One paper conducted field tests in
Athens, Greece for prototype cool color painted asphalt pavements which saw 15K temperature
reductions [026]. It was evident that not just albedo modifications have been examined in the
studies ‐ permeable pavements was a key area of research. These pavements allow the air and
water to flow in the pavement voids, examples of such technologies being developed were:
porous asphalt/concrete, permeable pavers, grid pavers to incorporating sprinkler systems in
some cases. It was suggested that when wet such cool pavement technologies may remain cooler
than the non‐permeable equivalents – however the dry conditions may have the opposite effect
[068, 073]. A recent study into the heat balance characteristics of pervious and impervious
concrete pavements by Kevern, Iowa, measured samples of each for their temperatures at various
depths as well as their heat storage capacity. He found that pervious concrete stores less energy
than traditional pavements so can help mitigate the UHI [228]. Water retentive paving materials
were tested for evaporation efficiency and heat budget in Japan and results found that surface
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