Review and Critical Analysis of International UHI Studies

oundary layer. The model calculates the upper boundary conditions, temperature, wind velocity
and water vapor pressure. Test sites are modeled under two scenarios, built areas, pavement and
structures and green areas. Results showed that the greatest causes of the nighttime temperature
increases was the release of heat from soil, the study proposed that the green surface balance of
the city was modified in order to control temperatures at night [024].
In Japan four simulations were carried out on the effects of building drag and heat storage in the
urban canopy on city temperatures. The simulations were: 1. a realistic study; 2. sensible heat flux
and radiation only; 3. drag effect of building on wind only; 4. no buildings presented. Each
simulation was carried out for an urban and a suburban case study and the simulation results
were tested again actually temperature readings for validation. The results showed that in
comparison with scenario 4, the contribution of heat flux from buildings was 49% in the urban
area and 20% in the suburban; wind reduction due to building drag for urban and suburban were
41% and 59% respectively and the effect of interaction between 2 and 3 was +10% for urban and
+20% in the suburban area [065].
Haider Taha, LBNL, discusses the heat island’s impact on air quality using uMM5 and CAMx
models with particular reference to ozone. The study also models albedo increase and its impact
on air temperature. Taha models the urban heat island in Sacramento California using a uMM5
model, the results of which show the UHI to start at around 1500 at 0 ~ 1°c higher than the
surrounds, at 1800 temperatures reach 0 ~ 2‐4°c, 2100 temperature peaks at 0 ~ 6°c and then they
slowly decrease, there is no difference in the early morning hours and then temperatures
decrease in comparison by 0 ~ 1‐2°c between mid morning and midday [049].
3.2.3 Simulations of Air Quality & CO2 Emissions Impacts
Air quality and CO2 emissions are regularly simulated. Poor air quality is linked to many
environmental and health problems. Much debate surrounds the topic of Greenhouse Gases and
their effect on global climate change, at a smaller/city scale environmental problems such as acid
rain and smog are effects of poor air quality. Poor air quality also exacerbates respiratory
conditions in humans and as such, this area is of particular concern.
There are four papers simulating the impacts of urban heat islands on air quality specifically, one
from Europe [139], one from North America [049], two from Asia [014, 141], and six that look at
the impacts of mitigation strategies on air quality, all from North America [012, 028, 041, 050, 063,
233].
The primary air pollutants simulated were NO2, CO2, CO, NOx and O3. Meteorology Models
commonly used were Mesoscale Meteorological Models (MM) and Photochemical models for the
pollutant concentrations such as Urban Air Shed Models for ozone and Biogenic Emissions
Inventory Systems (BEIS‐2) for biogenic emissions.
The following paragraphs provide a review of the key findings of some of the simulations
undertaken:
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