The Impact of Anthropogenic Heat on Formation of Urban Heat Island and Energy Consumption Balance

Abstract

This paper investigates the impact of anthropogenic heat on formation of urban heat island (UHI) and also determines which factors can directly affect energy use in the city. It explores literally the conceptual framework of confliction between anthropogenic heat and urban structure, which produced UHI intensity and affected energy consumption balance. It then discusses how these two factors can be affected and gives implication to the city and then focuses on whether actions should be taken for balancing adaptation and mitigation of UHI effects. It will be concluded by making the three important strategies to minimise the impact of UHI on energy consumption: landscaping, using albedo materials on external surfaces of buildings and urban areas, and promoting natural ventilation.

Full text

Hindawi Publishing Corporation
Urban Studies Research
Volume 2011, Article ID 497524, 9pages
doi:10.1155/2011/497524
Review Article
The Impact of Anthropogenic Heat on Formation of Urban Heat
Island and Energy Consumption Balance
P. Shahmohamadi, A. I. Che-Ani, K. N. A. Maulud, N. M. Tawil, and N. A. G. Abdullah
Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi Selangor, Malaysia
Correspondence should be addressed to A. I. Che-Ani, adiirfan@gmail.com
Received 26 December 2010; Revised 3 May 2011; Accepted 8 May 2011
Academic Editor: Andrejs Skaburskis
Copyright © 2011 P. Shahmohamadi et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
This paper investigates the impact of anthropogenic heat on formation of urban heat island (UHI) and also determines which
factors can directly affect energy use in the city. It explores literally the conceptual framework of confliction between anthropogenic
heat and urban structure, which produced UHI intensity and affected energy consumption balance. It then discusses how these
two factors can be affected and gives implication to the city and then focuses on whether actions should be taken for balancing
adaptation and mitigation of UHI effects. It will be concluded by making the three important strategies to minimise the impact
of UHI on energy consumption: landscaping, using albedo materials on external surfaces of buildings and urban areas, and
promoting natural ventilation.
1. Introduction
The urban built environment itself is related to global
changes in the increase of urban temperatures, the rate of
energy consumption, the increased use of raw materials,
pollution, and the production of waste, conversion of
agricultural to developed land, loss of biodiversity, and water
shortages [1]. It is clear that buildings not designed for
high climatic quality use more energy for air conditioning
and more electricity for lighting. Moreover, discomfort
and inconvenience to the urban population due to high
temperatures, wind tunnel effects in streets, and unusual
wind turbulence due to the incorrect use of energy.
With the concentration of anthropogenic activities into
urban areas, a climatic environmental problem, the “urban
heat island” (UHI), has emerged. A UHI is a climatic phe-
nomenoninwhichurbanareashavehigherairtemperature
than their rural surroundings as a result of anthropogenic
modifications of land surfaces, significant energy use, and its
consequent generation of waste heat. Thus, this proves to be
an unsustainable factor that leads to excessive energy use for
cooling and places the urban population at greater risk of
increased morbidity and mortality.
According to the above perspective and considering that
rapid and huge population growth is expected in the near
future, it becomes increasingly important to apply UHI
mitigation strategies in order to reduce energy consumption
and improve the quality of life with focusing on energy
consumption.
Thus, this paper investigates the anthropogenic heat fac-
tors that produce the UHI and result in the use of sig-
nificantly increased use of energy. Then, according to the
Oke’s energy balance conceptual model, all of the energy
which is absorbed by the surface through radiation or from
anthropogenic heat goes somewhere and warms the air above
the surface, it is evaporated away with moisture or is stored in
the material as heat. For energy saving, therefore, this paper
suggests some strategies to provide the best possible energy
saving solution.
2. Urban Heat Island
The majority of cities are sources of heat and pollution,
and the thermal structure of the atmosphere above them is
affected by the “heat island” effect. A UHI is best visualised
as a dome of stagnant warm air over the heavily built-up
areas of cities [2]. The heat that is absorbed during the day
by the buildings, roads, and other constructions in an urban
area is re-emitted after sunset, creating high-temperature
differences between urban and rural areas [3]. The exact

2Urban Studies Research
form and size of this phenomenon varies in time and space as
a result of meteorological, regional, and urban characteristics
[4]. Therefore, UHI morphology is greatly influenced by the
unique character of each city and its land uses. As seen in
Figure 1,Oke[4] stated that in a larger city with a cloudless
sky and light winds just after sunset, the boundary between
the rural and the urban areas exhibits a steep temperature
gradient to the UHI, and then the rest of the urban area
appears as a “plateau” of warm air with a steady but weaker
horizontal gradient of increasing temperature towards the
city centre. In Figure 1, the uniformity of the “plateau” is
interrupted by the influence of distinct intraurban land-uses
such as parks, lakes, and open areas (cool), and commercial,
industrial or dense building areas (warm).
In metropolitan areas, the urban core shows a final
“peak” in the UHI where the urban maximum temperature is
found. The difference between this value and the background
rural temperature defines the “UHI intensity” (ΔTu−r). The
intensity of the UHI is mainly determined by the thermal
balance of the urban region and can result in a temperature
difference of up to 10 degrees [3].
The UHI phenomenon may occur during the day or
during the night. Givoni [5] mentioned that the largest
elevations of the urban temperatures occur during clear
and still-air nights. Under these conditions, temperature
elevations of about 3–5◦C are common, but elevations of
about 8–10◦C were also observed.
Today, the majority of cities are around 2◦C warmer than
rural areas, and commercial and high-density residential
areas are hotter by 5 to 7◦C[6]. There are some main
parameters which influence the temperature increase in cities
and play a significant role in the formation of the UHI.
Therefore, UHI is caused by different factors that can be
divided into two types: (1) meteorological factors, such as
cloud cover, wind speed, and humidity; (2) urban structure
factors, such as ventilation, surface waterproofing, thermal
properties of fabric, surface geometry, and the like.
According to Landsberg [7], a UHI is present in every
town and city and is the most obvious climatic manifestation
of urbanisation. Clearly higher urban temperatures seriously
impact the electricity demand for air conditioning in build-
ings and increase smog production, as well as contribute
to increased emission of pollutants from power plants,
including sulphur dioxide, carbon monoxide, nitrous oxides,
and suspended particulates [3].
3. Conceptual Framework: Energy
Consumption Balance
3.1. Relation between Anthropogenic Heat and Urban Struc-
ture Factors and Formation of Urban Heat Island. Urban
areas are the sources of anthropogenic carbon dioxide
emissions from the burning of fossil fuels for heating and
cooling; from industrial processes; transportation of people
and goods, and the like, [1,8,9]. Increases in stationary
(industrial) and nonstationary (vehicles) pollutant sources
result in worsening atmospheric conditions [10]. The urban
environment affects many climatological parameters. Global
solar radiation is seriously reduced because of increased
Air temp rature
“Cliff”“Plateau” “Peak”
Park
Rural Suburban Urban
Commercial
district
ΔTu−r
e
Figure 1: Generalized cross-section of a typical UHI [4].
scattering and absorption [1]. Many cities in the tropics
experience weak winds and limited circulation of air which
helps the accumulation of pollutants [10]. The wind speed
in the canopy layer is seriously decreased compared to the
undisturbed wind speed and its direction may be altered.
This is mainly due to the specific roughness of a city,
to channelling effects through canyons and also to UHI
effects [1]. In addition, higher temperatures increase the
production of secondary, photochemical pollutants, and the
high humidity contributes to a hazy atmosphere.
Gartland [11] stated that although anthropogenic heat,
low wind speeds, and air pollution in urban areas can
contribute to UHI formation, there are two main reasons for
formation of UHI:
(1) because of impermeable and watertight urban con-
struction materials, moisture is not available to
dissipate the sun’s heat;
(2) dark materials in concert with canyon-like configu-
rations of buildings and pavement collect and trap
more of the sun’s energy. Temperatures of dark, dry
surfaces in direct sun can reach up to 88◦C during the
day while vegetated surfaces with moist soil under the
same conditions might reach only 18◦C.
Rapid urbanization leads to the development of a UHI;
Oke et al. [9,12] grouped these causes into the following five
categories, each of which represents change to the preurban
environment brought about by urbanization:
(1) anthropogenic heat;
(2) air pollution;
(3) surface waterproofing;
(4) thermal properties of fabric;
(5) surface geometry.
(1) Anthropogenic heat discharge in a city also con-
tributes to the UHI effect. Sources of anthropogenic heat
include cooling and heating buildings, manufacturing, trans-
portation, and lighting. Human and animal metabolisms are
also considered sources of artificial heat [13]. Heat from
these sources warm the urban atmosphere by conduction,
convection, and radiation. The contribution of anthro-
pogenic heat to the urban energy balance is largely a function
of latitude and season of the year. In a temperate city,
for example, anthropogenic heat flux may be a significant

Urban Studies Research 3
component of the energy balance in winter, yet a negligible
component in summer. In a polar settlement, artificial heat
flux may exceed solar heating year-round [14].
(2) Air pollution results from emissions of particulates,
water vapour, and carbon dioxide from industrial, domestic,
and automobile combustion processes. These atmospheric
pollutants change the urban net all-wave radiation budget
by (1) reducing the incident flux of short-wave (i.e., solar)
radiation, (2) re-emitting long-wave (i.e., infrared) radiation
from the urban surface downward to where it is retained
by the ground, and (3) absorbing long-wave radiation from
the urban surface, effectively warming the ambient air [4].
Lee [14] estimated that urban-rural differences in downward
long-wave radiation flux may be of the order of 10 percent,
depending on the city population and the presence of heavy
industry.
(3) Surface waterproofing refers to the predominance of
impermeable surface in urban areas. Buildings and paved
streets quickly shed precipitation into catchment basins,
creating an evaporation deficit in the city. Conversely, in
rural areas exposed soils and natural vegetation retain water
for evaporative cooling. A dry urban surface cover enhances
sensible heat transfer and suppresses latent heat flux whereas
moist rural surface suppress sensible heat transfer and
enhance latent heat flux.
(4) The fourth factor contributing to the formation of
UHIs relates to the thermal properties of the urban fabric.
The heat capacity, and consequently thermal inertia, of
urban construction materials such as concrete and asphalt
is greater than that of natural materials found in rural
environments. A greater heat capacity means that urban
materials absorb and retain more solar radiation than do
rural soils and vegetation. Reflection of short-wave solar
radiation is also affected by the properties of the urban
fabric. Urban albedos are, on average, 5–10 percent lower
than rural values [14]. This contributes to the greater diurnal
absorption of short-wave radiation in urban areas.
(5) The complex geometry of urban surfaces influences
air temperatures in two ways. First, increased friction created
by a rough urban surface (as compared to a smooth rural
surface) reduces horizontal airflow in the city. Mean annual
wind speeds within cities are approximately 30–40 percent
lower than mean annual wind speeds in the countryside [14].
Warm air stagnates in the urban canyons unless ventilated
by cool rural air. Lower wind speeds in the city also inhibit
evaporative cooling. And second, the complex geometry
of the urban surface changes the urban radiation budget.
During the day, vertical canyon walls trap (i.e., reflect and
absorb) short-wave radiation. Night-time losses of infrared
energy are also retarded due to the decreased sky view factor
below roof level. Rural surfaces, on the other hand, are com-
paratively smooth and therefore experience greater nocturnal
radiative flux divergence than a complex urban surface.
Anthropogenic heat is generated by human activity and
comes from many sources, such as buildings, industrial pro-
cesses, cars, and even people themselves [11]. Urban centres
(commercial centres) tend to have higher energy demands
than surrounding areas as a result of higher production
of anthropogenic heat. Though the UHI effect reduces the
Tab le 1: Urban and suburban characteristics important to UHI
formation and their effect on the energy balance of the earth’s
surface [11].
Characteristic contributing to
UHI formation Effect on the energy balance
Lack of vegetation Reduced evaporation
Widespread use of
impermeable surfaces Reduced evaporation
Increased thermal diffusivity of
urban materials Increased heat storage
Low solar reflectance of urban
materials Increased net radiation
Urban geometries that trap heat Increased net radiation
Urban geometries that slow
wind speeds Reduced convection
Increased levels of air pollution Increased net radiation
Increased energy use Increased anthropogenic heat
need for heating in the winter, this is outweighed by the
increased demand for air-conditioning during the summer
months [7], which in turn causes increased local and regional
air pollution through fossil-fuel burning electric power
generation. The pollution created by emissions from power
generation increases absorption of radiation in the boundary
layer [15] and contributes to the creation of inversion
layers. Inversion layers prevent rising air from cooling at
the normal rate and slow the dispersion of pollutants
produced in urban areas [16]. To determine how much
anthropogenic heat is produced in any region, all energy
use (commercial, residential, industrial, and transportation)
must be estimated. The sum is then divided by the region’s
area to enable comparisons of different cities to be made [11].
In developed countries where concerted action is being
taken on UHIs, the main concern is on the large increase in
power consumption in urban areas to cool down buildings,
with additional air-conditioners or a heavier usage of existing
air-conditioners. Higher air temperatures also mean that the
air quality deteriorates as a result of increased ozone and
pollution.
3.2. Energy Consumption Balance. As discussed previously,
there is no single cause of the UHI. In fact, many factors com-
bine to warm cities. Gartland [11] listed urban characteristics
contributing to UHI formation in Tabl e 1 . These characteris-
tics can be grouped into five main causes of UHI formation:
(1) increased anthropogenic heat;
(2) reduced evaporation;
(3) increased heat storage;
(4) increased net radiation;
(5) reduced convection.
The anthropogenic heat interacts with its environment
in a complex manner. To understand and simplify the
complexity, Oke [17] has suggested an equation called
the “energy balance” in which the heat generated by and

4Urban Studies Research
contained in an area could be calculated by this equation:
Q∗+QF=QH+QE+ΔQS+ΔQA,(1)
where, Q∗: the net all-wave radiation, QF: the anthropogenic
heat, QE:theturbulentlatentheatflux,QH: the turbulent
sensible heat flux, ΔQS: the sensible heat storage, ΔQA: the
net heat advection.
Net Radiation (Q∗). As shown below, net radiation encom-
passes four separate radiation process taking place at the
Earth’s surface [11]:
Net radiation =Incoming solar −Reflected solar
+ Atmospheric radiation
−surface radiation,
(2)
where, Incoming solar: the amount of energy radiating from
the sun, Reflected solar: the amount of solar energy that
bounces offa surface, based on the solar reflectance of the
material, Atmospheric radiation: heat emitted by particles
in the atmosphere, such as water vapour droplets, clouds,
pollution, and dust, and Surface radiation: heat radiated
from a surface itself.
The net all-wave radiation could then be calculated as the
difference between the incoming and outgoing parts [18,19].
The incoming short wave solar radiation was reported to
be attenuated due to the heavy smoke over urban areas,
[17,20]. The attenuation has been reported to be as high
as 33% in some cases [21] and has also been reported as
a cause of urban cool island [20]. In some other areas, on
the other hand, the attenuation has not been observed [19].
It is reported that the attenuation of incoming short-wave
radiation is compensated by albedo-related drop in outgoing
shortwave radiation and enhancement of incoming long-
wave radiation is compensated by an increase in outgoing
long-wave radiation due to the high surface temperature
emittance. It was reported that most of the attenuated part
is diffusedandreceivedbackandthenetdifference between
the urban and rural areas may not be more than 5%, [15,17].
Anthropogenic Heat (QF). Anthropogenic heat represents the
heat generated from stationary and mobile sources of an
area. It is reported that the QFmust either be converted to
radiations, sensible heat flux, or latent heat flux, or it is stored
[19]. This component has been modelled as the sum of heat
generated by the buildings, vehicles, and people, [22,23]or
as the residual of other terms [19].
Oke [17] reported that anthropogenic heat release could
be related to the population and its per capita energy
use. Taha [24] reported that the anthropogenic heat has
smaller effect than albedo and vegetation cover, and that it
is negligible in commercial and residential areas. Offerle et
al. [25], on the other hand, have considered it a significant
input in winter. It seems that depending on the area and its
energy use the term could be significant or negligible and it
could have varying diurnal, seasonal, or even weekly trends.
Turbulent Heat Fluxes (QE,QH). Turbulentheatfluxesare
comprised of the sensible and latent heat fluxes. These can
be directly derived from eddy correlation, or measured using
appropriate equipments. The heavily built urban areas are
reported to be responsible for increased sensible heat flux
whichisreportedtovaryasperthebuiltsurface[17]. The
intensity of latent heat flux, on the other hand, varies from
situation to situation as concluded by Hafner and Kidder
[26]. Grimmond [23] described the latent heat flux as the
largest portion in the surface energy balance (SEB) while
Masson [27] has neglected it in his proposed town energy
balance scheme. Although it is likely that the latent heat flux
will be low in an urbanized area due to decreased vegetation,
it could be high in vegetated parts of the city. The study
conducted by Suckling [28]reportedaBowenratio,sensible-
heat-flux-to-latent-heat-flux ratio, of up to 98% for a
suburban lawn. It was reported that the turbulent heat fluxes
vary with respect to the Q∗[25,29]. Thermal admittance and
ground moisture availability are reported to be other impor-
tant factors in quantifying the turbulent heat fluxes [17].
Storage Heat Flux (ΔQS). Christen and Vogt [19]reported
that due to the complicated configuration of surface
materials, orientations, and their interactions, the direct
measurement of storage heat flux in an urbanized area is
almost impossible. The term is, therefore, usually modelled
or determined as the residual of the SEB equation. It is
reported that an increase in the net all-wave radiation
directly increases the stored heat flux. Grimmond [23]found
an increase of around 60% in the monthly averaged day-time
ratio of stored heat flux to the net all-wave radiation with an
increase of net all-wave radiation.
NetHeatAdvection(ΔQA). Net heat advection could be
referred to as the inaccurate measurement due to spatial gra-
dient in temperature, humidity, and wind. It is suggested that
the effects of advection could be negligible provided that cau-
tion has been taken in deciding the measurement height [19].
The preceding discussion highlights how energy is trans-
formed to and from the Earth’s surface. The energy balance
equation is based on the first law of thermodynamics, which
states that energy is never lost. For a surface on the Earth, this
means that all of the energy absorbed by the surface through
radiation or from anthropogenic heat goes somewhere.
Either it warms the air above the surface, is evaporated away
with moisture, or is stored in the material as heat.
Other statistical data show that the amount of energy
consumed by cities for heating and cooling offices and
residential buildings has increased significantly in the last
two decades. Emmanuel [30] has shown the rate of energy
consumption of three countries, US, UK, and Sri Lanka (in
Tabl e 2). A comparison of energy-use patterns between a
developed country like the US and a developing country like
Sri Lanka shows that transportation and activities within
buildings consume a considerable share of energy in both
cases.
Increased anthropogenic heat has a direct effect on build-
ing energy consumption that an increase in the production
of anthropogenic heat leads to raise the electricity demand

Urban Studies Research 5
Anthropogenic
heat
Two main factors
of UHI formation
Urban structure
factors
Ventilation
system
Surface
waterproofing
Thermal
properties of
fabric
Urban geometry
Density of built-
up area
Land ses
Increase urban
temperature
UHI intensity
Increase energy consumption
u
Figure 2: The process of increasing energy consumption.
Tab le 2: Patterns of commercial energy consumption [30].
Activity Energy consumption (% of total country needs)
US U.K. Sri Lanka
Industry 41.2 32.0 9.9
Transportation 21.0 18.0 16.4
Building energy
needs 28.0 48.0 67.0
Agriculture/other 7.7 2.0 6.7
for cooling and the production of carbon dioxide and other
pollutants.
Therefore, it can be concluded that increasing the
production of anthropogenic heat, which leads to raised
temperatures and generates a UHI that provides a warm air
canopy over the city. Consequently, it causes significantly
increased energy consumption to heat and cool buildings.
This process is summarised in Figure 2.
This paper has tried to develop a concept to show the
conflict between anthropogenic heat and urban structure
factors can affect the energy balance.
This paper highlights energy consumption, anthro-
pogenic heat, and urban structure factors as the key
components; according to Bridgman et al. [31], replacing
grass, soil, and trees with asphalt, concrete, and glass; the
rounded, soft shapes of trees and bushes with blocky, angular
buildings and towers; artificial heat from buildings, air
conditioners, industry, and automobiles; efficiently disposing
of precipitation in drains, sewers, and gutters, preventing
surface infiltration; emitting contaminants from a wide range
of sources, which with resultant chemical reactions can
create an unpleasant urban atmosphere, higher production
of anthropogenic heat, and an increased UHI intensity.
Compiling the three key components into a concept is
meaningful in reducing UHI effects and achieving energy
consumption balance. The relationship between the three
key components is presented in the conceptual model shown
in Figures 3and 4.
In Figure 3, the shaded area represents the UHI intensity.
A greater conflict between anthropogenic heat and urban
structure factors causes higher UHI intensity. With increas-
ing UHI intensity, energy consumption becomes imbalanced
while Figure 4 shows that by mitigating UHI effects, energy
consumption balance can be achieved.
This process can be described in the following way:
UHI ↓= ECB,
UHI ↓= AH ↓+USF ↓,
AH ↓+USF ↓= ECB,
(3)

6Urban Studies Research
Energy
consumption
balance
Anthropogenic
heat
Urban
UHI intensity
stru tcure
Figure 3: Conflict between anthropogenic heat and urban structure
factors, creation of UHI, and its effect on energy consumption
balance.
Energy
consumption
balance
Anthropogenic
heat
Urban
stru tcure
UHI intensity
Figure 4: Mitigation of UHI has direct effect on energy consump-
tion balance.
where, UHI is the urban heat island (↓decrease), ECB is the
energy consumption balance, AH is the anthropogenic heat,
USF is urban structure factors.
Therefore, by decreasing anthropogenic heat and urban
structure factors, mitigation of UHI effects is achievable.
Although decreasing the anthropogenic heat is depen-
dent on urban structure factors, an optimal and realistic
solution is to focus on urban structure factors, such as
natural ventilation, surface materials and landscape, or
vegetation covers to decrease UHI intensity and create energy
consumption balance;
ECB =MEC + LEC + NVEC,
MEC =LEC =NVEC,
(4)
where, MEC is the amount of reflectivity and emissivity of
surface materials, LEC is the amount of appropriate land-
scape or vegetation covers; NVEC is the appropriate amount
of wind introduced into a built environment; an appropriate
solution is adequate vegetation, natural ventilation, and high
albedo materials, which results in an acceptable impact on
energy consumption balance.
Under such circumstances, a balanced urban environ-
ment can be created (Figure 5). This means that adding
natural ventilation, vegetation covers, and high-albedo and
high-emissivity materials in buildings can reduce UHI effects
and balance energy consumption. This will be described in
the next section.
4. Mitigation of Urban Heat Island Effects:
Achieving Energy Consumption Balance
The reduction of the energy consumption of buildings by
combining techniques to improve the thermal quality of
the ambient urban environment with the use of up-to-date
alternative passive heating, cooling, and lighting techniques
can partly decrease these kinds of environmental problems.
Asimakopoulos et al. [3] stated that some of the factors
that usually have a negative effect on the low energy con-
sumption include the design and construction of urban bui-
ldings.
(a) The layout of the basic road network with a specific
orientation. This layout affects the buildings on either
side of the road, giving them an orientation that, in
most cases, is not suitable for implementing solar and
energy saving techniques.
(b) The relationship between the height of a building and
the width of the road, which causes overshadowing
and thus prevents access to direct sunlight in living
spaces.
(c) The relationship between plot frontage and depth,
which can determine how many internal spaces will
have a southern aspect.
(d) Densely built urban centres, which result in the
obstruction of airflow and sunlight by the walls of tall
buildings.
(e) A lack of greenery that has been replaced by concrete
and tarmac.
(f) Overshadowing caused by adjacent buildings and
other landscape features, which is difficult to avoid.
(g) Building regulations and codes that in most cases
determine the dimensions of a building and thus its
geometrical form and its position on the plot.
It also must be noted that higher temperature and
less intensive winds are causes of UHI effects. In addition,
inappropriate orientation, high density, and shading can
directly affect UHI formation. If proper interventions are
implemented in urban design, better climate conditions
will be achieved when serious overheating problems occur.
A large number of air-conditioning appliances leads to
increased cooling loads during the summer and to over-
consumption of electric energy, which also increase peak
energy demand and creates failures in the energy transport
network. Energy saving techniques that can be applied in a

Urban Studies Research 7
Natural
ventilation
Materials Landscape
ECB
Figure 5: Achieve energy consumption balance by providing bal-
ance with natural ventilation, high-albedo materials, and vegetation
covers.
building includes two kinds of strategies that can be divided
into urban elements (macro scale) and building elements
(micro scale) strategies. The first strategy includes the energy
conservation methods, which involve application of some
strategies in urban areas, while the second method includes
strategies for buildings. This paper focuses on three main
strategies in each scale.
The combination of these two categories will provide the
best possible energy saving solution. According to the above
considerations these strategies are described in the following
sections.
4.1. Promoting Natural Ventilation. Natural ventilation is the
most effective passive cooling technique that can provide
cooling during both day and night, while night ventilation
is a very effective strategy in hot climates [3]. Some strategies
for buildings can provide natural ventilation and save energy.
Therefore, this paper recommends some strategies to achieve
this aim.
(1) Natural ventilation by arranging the openings in bui-
ldings to face the prevailing wind can provide effi-
cient natural ventilation and create a healthy indoor
air quality.
(2) Natural ventilation by ventilated roofs eliminates
overheating.
(3) Variation in building height can create better wind at
higher levels if differences in building heights bet-
ween rows are significant.
(4) Building orientation with adequate gaps is useful for
good airflow.
(5) Increasing building permeability by providing void
decks or pilots at ground level or at midspan.
4.2. Using Appropriate Materials on External Surfaces of the
Buildings. An increase in the surface albedo has a direct
impact on the energy balance of a building. Cities and urban
areas in general are characterised by a relatively reduced
effective albedo as a result of two mechanisms [1].
(1) Darker buildings and urban surfaces absorb solar
radiation.
(2) Multiple reflections inside urban canyons signifi-
cantly reduce the effective albedo.
As Asimakopoulos et al. [3] stated, numerous studies
have been performed to evaluate the direct effects of albedo
change and demonstrate the benefits of using reflective
surfaces. In all cases, the roof temperatures are significantly
reduced, but the degree to which the cooling load decreases
depends on the structure of the roof and on the overall
thermal balance of the building. Surface materials with a
high albedo index to solar radiation reduce the amount
of energy absorbed through building envelopes and urban
structures, and keep the surface cooler. Building materials
can be divided into pavement materials, roof materials, and
building envelopes.
Therefore, this paper recommends using reflective mate-
rials on external surface of building to reduce UHI effects and
improve the urban environment.
4.2.1. Using High-Albedo Materials on Building Surfaces. A
material with high albedo can reduce the solar heat gain
during the daytime. The surface temperature of the material
is lower than that of a material with low albedo. Because
the urban ambient temperature is associated with the surface
temperatures of the building fac¸ade, lower surface tempera-
ture can obviously decrease the ambient air temperature and
eventually contribute to better urban thermal environment.
4.2.2. Using White Pavement Instead of Asphalt. Asphalt
temperature can reach 63◦C and white pavements only
reach 45◦C[1]. Lower surface temperatures contribute to
decreasing the temperature of the ambient air because the
heat convection intensity from a cooler surface is lower. Such
temperature reductions have a significant impact on cooling
energy consumption in urban areas.
4.2.3. Using Cool Roofs. Cool roofs reduce building heat-
gain, create saving air conditioning expenditures, enhance
the life expectancy of both the roof membrane and the
building’s cooling equipment, improve thermal efficiency of
the roof insulation, reduce the demand for electric power,
reduce resulting air pollution and greenhouse gas emissions,
provide energy savings, and mitigate UHI effects.
4.3. Providing Appropriate Landscape. Providing an appro-
priate landscape in building can also contribute to energy
consumption reduction. The impact of an appropriate land-
scape around a building on energy consumption and sur-
rounding temperature regime is very important. Landscap-
ing the surrounding area is a basic criterion to improving the

8Urban Studies Research
external climatic conditions. As mentioned by Asimakopou-
los et al. [3], shading from trees can do the following.
(1) Significantly decrease the energy required for cooling.
(2) Decrease the rate of heat convection inside buildings
because of shaded surfaces that have a lower temper-
ature.
(3) Decrease the radiation exchange of the wall with the
sky.
Sailor [32] considers that the low evaporative heat flux
in cities is the most significant factor in the development
of a UHI. When vegetation is placed on urban surfaces,
thermal balances can shift to new conditions that are closer
to the cooler conditions of rural areas. It is estimated that
1460 kg of water is evaporated from an average tree during
a sunny day, which consumes about 860 MJ of energy; this
offers a cooling effect outside a building that is equal to five
average air conditioners [1]. Furthermore, to reduce energy
consumption, various types of trees and vegetation covers in
different parts of the buildings must be considered.
Therefore, this paper recommends using green spaces in
vertical and horizontal layers.
4.3.1. Vertical Green Spaces. Green spaces in some parts of
buildings that provide natural ventilation or appropriate
landscapes in different layers or floors of buildings with
a multiuse function can significantly decrease the energy
required to cool buildings.
4.3.2. Horizontal Green Spaces. Greenspacesonroofsabsorb
heat, decrease the tendency towards thermal air movement,
and filter air movement. Through the daily dew and evapora-
tion cycle, plants on vertical and horizontal surfaces are able
to cool cities. In the process of evapotranspiration, plants
use heat energy from their surroundings when evaporating
water.
5. Conclusions
There is strong scientific evidence that the average temper-
ature of the earth’s surface is rising because of increased
energy consumption. Global warming has a major impact
on human life and the built environment. Therefore, an
effort must be made to reduce energy use and to promote
green energies, particularly in the building sector. Energy
balance can be achieved by minimising energy demand,
rational energy use, recovering heat, and using more green
energies. This paper was a step towards achieving that goal.
The adoption of green or sustainable approaches to the way
in which society is run is seen as an important strategy in
finding a solution to the energy problem. As discussed in
this paper, one of the most important factors that increases
energy use is the formation of urban heat islands. Therefore,
this paper considers the effects of UHI and by recognising
them, proposes beneficial solutions that can lead to energy
consumption balance.
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