Effect of tree planting design and tree species on

Landscape and Urban Planning 138 (2015) 99–109
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Landscape and Urban Planning
journal homepage: www.elsevier.com/locate/landurbplan
Research Paper
Effect of tree planting design and tree species on human thermal
comfort in the tropics
Loyde Vieira de Abreu-Harbich a,∗ , Lucila Chebel Labaki a , Andreas Matzarakis b
a
b
School of Civil Engineering, Architecture and Urban Design, State University of Campinas, Rua Saturnino de Brito, 224, 13083-850 Campinas, Brazil
Faculty of Environment and Natural Resource, Albert-Ludwigs-University Freiburg, Werthmannstrasse 10, D-79085 Freiburg, Germany
h i g h l i g h t s
•
•
•
•
Single and clusters of trees are quantified on a quantitative manner.
Thermal comfort conditions are strong influenced by solar radiation and wind.
Must appropriate tree for the improvement of thermal comfort conditions are Caesalpinia pluviosa.
Reduction of Tmrt can improve thermal comfort conditions about 16◦ C (PET) during summer condition.
a r t i c l e
i n f o
Article history:
Available online 12 March 2015
Keywords:
Human thermal comfort
Physiologically equivalent temperature
Mean radiant temperature
Tree planting design
Tropical climate
Brazil (Campinas)
a b s t r a c t
Trees behave in different ways on microclimate due to mainly distinct features of each species and
planting strategies especially in the tropics. This paper quantifies the daily and seasonal microclimate
behavior of various tree species with different planting design either individual or in clusters. This specific
knowledge is an important step in the development of urban design guidelines based on the shading of
trees and climate adaptation in urban areas in the tropics. It focuses on human thermal comfort based
on the physiologically equivalent temperature (PET) for different species. Twelve species were analyzed:
Handroanthus chrysotrichus (Mart. ex A.DC.) Mattos, Jacaranda mimosaefolia D. Don., Syzygium cumini
L., Mangifera indica L., Pinus palustris L., Pinus coulteri L.; Lafoensia glyptocarpa L., Caesalpinia pluviosa F.,
Spathodea campanulata P. Beauv., Tipuana tipu F., Delonix indica F. and Senna siamea L. The results show
that shading of trees can influence significantly human thermal comfort expressed by (PET). The species
C. pluviosa F. presents the best possibility in terms of PET because it can reduce between 12 and 16 ◦ C for
individual trees cluster can reduce between 12.5 and 14.5 ◦ C. Appropriate vegetation used for shading
public and private areas is essential to mitigate heat stress and can create better human thermal comfort
especially in cities. The results can be seen as a possibility of improvement of outdoor thermal comfort
conditions and as an important step in order to achieve sustainability in cities.
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
An important characteristic of tropical cities is urban greenery
that creates shading along streets and in residential areas and can
assist in the development of adaptation possibilities against climate change. It also acts as a carbon sink, relative to the amount
of green coverage (Abreu-Harbich, Labaki, & Matzarakis 2013a,
2013b; Emmanuel, 2005; Emmanuel, Rosenlund, & Johansson,
2007; Grimmond, 2007; Lin, Matzarakis, & Hwang, 2010). The
∗ Corresponding author at: Rua Saturnino de Brito, 224, Caixa Postal 6021, 13083852 Campinas, Brazil. Tel.: +55 0193521 2384; fax: +55 19 3788 2411.
E-mail address: loydeabreu@gmail.com (L.V. de Abreu-Harbich).
http://dx.doi.org/10.1016/j.landurbplan.2015.02.008
0169-2046/© 2015 Elsevier B.V. All rights reserved.
characteristics of the various surfaces in urban spaces and their
behavior with respect to incident solar radiation have serious
impacts on the urban environment (Guderian, 2000). The study
of vegetation in the control of incident solar radiation, and as
a regulator of urban climatic changes involves qualifying and
quantifying the influence of trees on human thermal comfort
(Abreu-Harbich, Labaki, & Matzarakis, 2012; Matzarakis, 2013;
Matzarakis & Endler, 2010; Shashua-Bar, Pearlmutter, & Erell, 2009;
Shashua-Bar, Potchter, Bitan, Boltansky, & Yaakov, 2010; Streiling &
Matzarakis, 2003; Yilmaz, Toy, Irmaka, & Yilmaz, 2007). Numerous
studies focusing on trees and their benefits in urban environment
have been published (Bernatzky, 1979; Cardelino & Chameides,
1990; Dimoudi & Nikolopoulou, 2003; Heisler, 1977; Herrington,
1977; McPherson, Nowak, & Rowantree, 1994; Meyer & Bauermel,
100
L.V. de Abreu-Harbich et al. / Landscape and Urban Planning 138 (2015) 99–109
1982; Montague & Kjelgren, 1998; Oke, 1989; Santamouris, 2001;
Shashua-Bar & Hoffman, 2000; Shashua-Bar et al., 2010). Various methodologies confirm that vegetation can influence urban
microclimate, improve human thermal comfort, and decrease the
potential for health impairment of urban populations (Akbari,
2002; Akbari, Rosenfeld, Taha, & Gartland, 1996; Dimoudi &
Nikolopoulou, 2003; Mayer, Salovey, & Caruso, 2008; Santamouris,
2001; Streiling & Matzarakis, 2003). Arboreal species behave in
diverse ways in outdoor spaces, especially in terms of differences
in shade, with previous studies quantifying these benefits (BuenoBartholomei & Labaki, 2003; Lin et al., 2010; Shahidan, Shariff,
Jones, Salleh, & Abdullah, 2010; Shashua-Bar & Hoffman, 2000;
Shashua-Bar et al., 2009, 2010).
Urban trees can modify air temperature, increase air humidity, reduce wind speed, and modify air pollutants (Streiling &
Matzarakis, 2003). It has been confirmed that the positive effects
on the bioclimatic conditions of a city, the mean radiant temperature (Tmrt ) and the human biometeorological thermal index – the
physiologically equivalent temperature (PET), of single trees and
clusters are distinct because of differences between areas with
trees and without trees. Local air temperature can be influenced
by green coverage and leaf area index (LAI), which are important arboreal characteristics (Tsutsumi, Ishii, & Katayama, 2003).
Some studies confirm that specific features of species, like structure and density of the treetop, size, shape and color of leaves, tree
age and growth, can influence the performance of solar radiation
attenuated by canopy, air temperature and air humidity (AbreuHarbich et al., 2012; Bueno-Bartholomei & Labaki, 2003; Correa,
Ruiz, Canton, & Lesino, 2012; Gulyás, Unger, & Matzarakis, 2006;
Scudo, 2002; Shashua-Bar et al., 2009). Tree canopies are able to
modify to microclimatic environments because of reflection, transmission and absorption of solar radiation and control wind speed
(Steven, Biscoe, Jaggard, & Paruntu, 1986). In tropical climates,
the possibility of changing wind conditions and shade will modify
the microclimate and improve human thermal comfort (Lin et al.,
2010).
In Brazil, it was recently concluded that outdoor thermal comfort is closely related to urban tree management (Spangenberg,
Shinzato, Johansson, & Duarte, 2008). Various Brazilian researchers
have used PET, but these indexes need to be adapted to the local
climate (Monteiro & Alucci, 2010).
Studies have shown that shade and increase wind speed can
improve human thermal comfort in tropical climates (AbreuHarbich et al., 2013a; Akbari & Rose, 2008; Akbari & Taha, 1992;
Lin et al., 2010). Therefore, planting trees is a good solution for
improving thermal comfort in tropical cities.
The shade cast by trees, and the amount of radiation filtered, is
influenced by the form and density of the canopy. The amount of
radiation intercepted depends on the density of the twigs, branches,
and leaf cover. These elements influence the overall characteristics
of tree shape and density (Abreu-Harbich et al., 2012; Brown &
Gillespie, 1995; Scudo, 2002). Tree shade qualities are also influenced by the individuality of trunks and of leaves, which should be
considered (Abreu-Harbich et al., 2012; Shashua-Bar et al., 2010).
As an example, tree species in Brazil can attenuate solar radiation from 76.3 to 92.8% in the summer months (Abreu-Harbich
et al., 2012; Bueno-Bartholomei & Labaki, 2003). These results confirm that the structure of the crown, and the dimension, shape
and color of leaves influence the levels of reduction in solar radiation. It is important to observe the vegetation parameters which
affect solar radiation and wind in relation to their thermal control
strategies, and their different green elements (Table 1). It is also
important to quantify the thermal conditions of trees with field
measurements, and to combine these results with the tree features
to improve green design. Accordingly, planting the right trees in
the cities can improve and adapt the cities to climate change.
Our aim was to quantify the daily and seasonal microclimate
behavior of various tree species in different planting configurations.
Such knowledge is important in the development of urban design
guidelines based on the shading of trees and climate adaptation in
urban areas of the tropics. We have focused on thermal comfort of
humans based on the PET for different tree species. We intend to
quantify these affects by providing quantitative results, which can
be applied in tropical regions.
2. Methodology
2.1. Study area
Our study was conducted in Campinas (22◦ 48 57 S; 47◦ 03 33
W; 640 m elevation), in the southeast of Brazil. It is one of the
larger cities in the country, with 1.1 million inhabitants and a
very high population density of 1300/km2 (Brazil, 2010). The
Köppen-Geiger climate classification of the city is subtropical
(Cwa; Kottek, Grieser, Beck, Rudolf, & Rubel, 2006), with less rainfall in winter, and rainy, warm-to-hot days in summer. Mean
annual air temperature is 22.3 ◦ C and annual rainfall 1411 mm.
Rain is predominant from November to March, with dry periods of 30–60 days in July and August. The summer period is
from November to April, with average maximum temperatures
between 28.5 and 30.5 ◦ C and minimum temperatures between
11.3 and 13.8 ◦ C. The warmest month is February, with an average
temperature of 24.9 ◦ C (maximum 30.0 ◦ C and minimum 19.9 ◦ C).
The winter season is June, July and August, with maximum temperatures between 24.8 and 29.1 ◦ C and minimum between 11.3
and 13.8 ◦ C. The coldest month is July, with an average temperature of 18.5 ◦ C (maximum 24.8 ◦ C and minimum 11.3 ◦ C). The
prevalent wind direction is southeast, with a mean annual speed
of 1.4 m/s. Annual sunshine duration is 2373 h, and the mean
daily solar radiation is 4.9 kWh/m2 . Weather variations in Campinas are caused by regional atmospheric circulation shifts and
diverse topography. There are tropical, equatorial continental,
tropical Atlantic (the most common) and polar (especially polar
Atlantic) systems, and these modify the regional climate (Nunes,
1997).
2.2. Sites and observations
The scales adopted in field measurement for this research
were instantaneous and microclimatic, which allowed for assessing
weather conditions and not climate. However, the “in loco” climate, mainly within 1 km, was influenced by local environmental
parameters (solar radiation, air temperature, relative humidity and
wind speed), and by macroclimatic and mesoclimatic conditions. In
studies concerned with qualifying and quantifying trees and their
benefits at the micro scale, similar surrounding conditions should
be considered: no shade from buildings or other trees; uniformity
of conditions around trees related to topography, lack of pavement
and buildings nearby; standardization of the surface at the measuring points; and time of exposure, with few or no clouds. The criteria
for the choice of species to be studied were those most used in tree
planting programs of the Campinas city government. Trees were
required to meet the following conditions: mature; their physical characteristics were representative of their species; they were
located in areas suitable for measurement; specifically unshaded
by nearby trees or buildings; accessible topography and sufficient
area for equipment around the species; and no interference by
passers. The large gap of study different trees species is because
they behave in different ways in microclimate. As well, it is necessary to consider the biodiversity for sustainability of urban green
on cities.
L.V. de Abreu-Harbich et al. / Landscape and Urban Planning 138 (2015) 99–109
101
Table 1
Thermal control based in trees features.
Fig. 1 lists the date of measurements, and the tree species for
each site in the urban area of Campinas. Twelve species were
selected and grouped accordingly:
• Single trees; Handroanthus chrysotrichus (Mart. ex A. DC.) Mattos,
Jacaranda mimosaefolia D. Don., Syzygium cumini L., M. indica L.,
Pinus palustris L., Pinus coulteri L.
• Single trees and clusters; Lafoensia glyptocarpa L., Caesalpinia pluviosa F., Spathodea campanulata P. Beauv., Tipuana tipu F.
• Clusters; Delonix indica F. and Senna siamea L.
In supplementary material, extra tables show individual and
clustered trees, along with characteristics such as crown, trunk
and leaf. All measurement fields were situated in the urban area
of Campinas.
2.3. Measurement
For each individual tree and tree clusters, air temperature and
humidity, wind speed, and global radiation were collected for in the
shade and in the sun during summer and winter periods between
2007 and 2010. The sampling interval was 10 min every hour over
a period from 6:00 AM to 6:00 PM Air temperature and humidity
data were collected with a Testo data logger, model 175-1. Two
tripods were fixed in the shadow and in the sun. Wind speed data
were collected at a fixed site with a Testo anemometer, model
0635-1549, connected to a multifunction recorder, model 445. The
sensors were positioned at a height of 1.1 m. All recordings were
protected from solar radiation using special shelters designed for
outdoor measurements (Fig. 2).
Solar radiation was measured using two tube solarimeters, type
TSL (Delta-T Devices© ). Sensors from the tube solarimeters were
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L.V. de Abreu-Harbich et al. / Landscape and Urban Planning 138 (2015) 99–109
Fig. 1. Studied trees and clusters.
connected to a logger, model DL2, also from Delta-T Devices© .
The equipment measured average irradiance (W/m2 ) in situations
where the distribution of radiant energy was not uniform, such as
beneath tree crowns and greenhouses. The spectral response corresponded to visible and near infrared radiation (350–2500 nm). For
individual and clusters trees, one of the solarimeters was positioned
in the middle of the tree shadow, while the second was positioned
in sunlight.
2.4. Methods and analyses
Modern human biometeorological methods use the energy balance of the body (Höppe, 1993, 1999) to extract thermal indices for
describing effects of the thermal environment on humans (Mayer,
1993; VDI, 1998). For this study, we used values of meteorological
data obtained every minute in the 10-min sampling time to calculate PET (Mayer & Höppe, 1987). To quantify the thermal comfort
provided by shade of trees, meteorological data (air temperature,
air humidity, wind speed and global radiation) collected from field
measurements were used to calculate PET with the assistance of
RayMan software (Matzarakis, Rutz, & Mayer, 2007, 2010). PET
estimation was dependent on atmospheric influences, primarily
clouds and other meteorological variables such as vapor pressure or particles. Tree morphologies acting as obstacles were also
included. The primary input parameters to RayMan in the study
were air temperature, air humidity, wind speed, and total solar
radiation. The comfortable range that has been used is the European one (Matzarakis & Mayer, 1996) in combination of the tropical
produced/adjusted for Taiwan by Lin and Matzarakis (2008). For
European, the range of thermal comfort is between 18–23 ◦ C and
for tropical 26–30 ◦ C, and for extreme heat stress, higher than 41
or 42 ◦ C.
The attenuation of solar radiation was dependent on tree features such as the density of the twigs and branches, and leaf cover.
The percentage of radiation attenuated by each tree, or cluster
of trees, was obtained by the method of Bueno-Bartholomei and
Labaki (2003), where measurements of solar radiation in the shade
and in the sunlight were made simultaneously, in accordance with
the expression:
AT =
Ssun − Ssh
× 100
Ssun
(1)
For the time interval considered, AT is solar radiation attenuation (%), Ssun is the area (kWh/m2 ) for the total incident energy
collected by the solarimeter in sunlight, and Ssh is the area
(kWh/m2 ) for the total incident energy in the shade.
The plant area index (PAI) describes the amount of foliage when
referring to all light-blocking elements (stems, twigs, leaves, etc.),
while the leaf area index (LAI) accounts only for leaves (Holst et al.,
2004; Nackaerts, Coppin, Muys, & Hermy, 2000; Neumann, Hartog,
& Shaw, 1989). Hemispherical photography (“fish-eye”) in orthogonal projections was used for specific points below canopies for
each individual tree, and clusters of trees. These pictures look for
sun gaps in the canopy layer where direct or diffuse radiation is able
to reach the ground (Abreu-Harbich et al., 2012; Tsutsumi et al.,
2003). To obtain the PAI of each analyzed tree, the Sky View Factor (SVF) is calculated based on fish-eye pictures using RayMan Pro
software, where the sky area is replaced by the area of branches
and green leaves.
2.5. Applied model
The RayMan model was applied to analyze the long-term
changes in thermal bioclimate caused by differences in tree shading. RayMan allows the calculation of Tmrt , which is used to calculate
thermal bioclimatic indices, or PET. Tri-dimensional models of vegetation were designed based on features of the studied trees, and
included height, crown radius, trunk length and trunk diameter. In
addition, the SVF of each individual tree, and cluster of trees, was
included in the simulation.
L.V. de Abreu-Harbich et al. / Landscape and Urban Planning 138 (2015) 99–109
103
Fig. 2. Field measurements equipment.
PET was calculated for each tree during over 7 years
(2003–2010). Meteorological data used in this simulation were
obtained from an urban automatic agro-meteorological station
with a CR23X data logger (Campbell Scientific Inc.© ) at the Agronomic Institute of Campinas (IAC) on Santa Elisa Farm (22◦ 54 S;
47◦ 05 W; 669 m elevation). This site is in northern Campinas, 5 km
from the city center. This station was not affected by surrounding obstacles, and provided meteorological data representative of
the study areas. The meteorological data provided were air temperature, relative humidity, wind speed, and solar radiation over a
7-year period (25 June 2003–31 December 2010). These data points
were sampled every 60 min.
3. Empirical findings
For the quantitation of thermal comfort provided by tree
canopies during different seasons, daily data results for air temperature (Ta ) in summer and winter are shown in Figs. 3 and 4,
respectively. Daily data results for PET in summer and winter are
presented in Figs. 5 and 6, respectively.
Figs. 3–6 show the differences in temperature between sunlight
and shade from 6:00 AM to 6:00 PM. The cooling effects of tree
shading were more evident from 10:00 AM to 2:00 PM compared
with those in the early morning and evening.
In the summer, the air temperature in direct sunlight and shade
for individual trees showed minor differences. The air temperature for tree clusters however exhibited distinct patterns (Fig. 3).
Individual trees such as Handroanthus chrysotrichus, S. cumini, C.
pluviosa, T. tipu reduced the air temperature by 0.9–2.8 ◦ C between
10:00 AM and 2:00 PM. Individual S. cumini exhibited the best shade
behavior, with 2.8 ◦ C of cooling in the shade during this period. Clusters of C. pluviosa or T. tipu reduced the air temperature by 0.7–2 ◦ C
during the same period.
In the winter, air temperature reduction results differed (Fig. 4).
The air temperature in the shade, or in direct sunlight, for individual trees (Handroanthus chrysotrichus, P. palustris, P. coulteri, L.
glyptocarpa, M. indica and S. campanulata) was not significantly
different. For S. cumini and C. pluviosa, the air temperature was
reduce by 1.9–2.6 ◦ C from 10:00 AM to 2:00 PM. For clusters of
trees (C. pluviosa, S. campanulata and D. indica), the air temperature was reduced by 0.1–2.4 ◦ C from 10:00 AM to 2:00 PM over
the same period. C. pluviosa exhibited the best cooling effects,
whether individual or in clusters. With respect to individual trees
of this species, the air temperature was reduced by 2.2–2.7 ◦ C in the
shade during the warmest daylight hours; a cluster of these trees
reduced the air temperature until 2.0 ◦ C in the shade over the same
period.
PET values observed for summer (Fig. 5) showed that the shade
cast by individual trees, such as Handroanthus chrysotrichus, S.
cumini, C. pluviosa, and T. tipu, reduced temperatures by as much as
16 ◦ C. Shading from C. pluviosa and T. tipu tree clusters reduced the
air temperature by 11.2–14.4 ◦ C from 10:00 AM to 2:00 PM. C. pluviosa exhibited the best effects with respect to improving thermal
comfort. An individual tree of this species reduced air temperature
by 12–16 ◦ C during daylight hours, while a cluster of these trees
reduced air temperature by 12–14.4 ◦ C.
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Fig. 3. Diurnal courses of air temperatures during the summer.
Fig. 4. Diurnal courses of air temperatures during the winter.
Fig. 5. Diurnal courses of physiologically equivalent temperature (PET) (◦ C) during the summer.
L.V. de Abreu-Harbich et al. / Landscape and Urban Planning 138 (2015) 99–109
105
Fig. 6. Diurnal courses of physiologically equivalent temperature (PET) (◦ C) during the winter.
The PET values for winter (Fig. 6) show that individual S. cumini,
M. indica, C. pluviosa and L. glyptocarpa provided the best results
with respect to improvements in thermal comfort. These trees
resulted in a reduction of air temperature of 7.4–17.5 ◦ C from
10:00 AM to 2:00 PM. Individual Handroanthus chrysotrichus without leaves exhibited the worst results in terms of cooling effects,
with the air temperature reduced by only 0.6–1.1 ◦ C over the same
period. A cluster of C. pluviosa and L. glyptocarpa trees had the
best cooling effects, with their shading reducing the air temperature by 7.8–14.4 ◦ C. Clusters of other tree species did not result in
improvements for thermal comfort.
A comparison of the summer and winter PET results showed that
the cooling effects of trees, either individual or in clusters, in the
summer were greater than in the winter (Table 2). Using air temperature as factors the differences between sun and shade are less
2.8 ◦ C in summer. For PET the differences are much higher ranging
from 1 up to 16 ◦ C. For individual trees, the differences are higher
than for clusters because of the effect of wind on PET. This behavior
can be explained by the phenology of each species. We have presented the attenuated solar radiation over the year, along with PAI
(Fig. 7).
For individual trees, the PAI results for the coniferous species P.
palustris and P. coulteri, were 47 and 34% respectively. These trees
are characterized by a pyramidal crown, a narrow canopy, and a
moderate area of sunny spots with 53 and 66% SVF for P. palustris
and P. coulteri, respectively. The cooling effects can be explained
by solar radiation attenuated by the crown (79.7 and 83.8% during
summer; 69.8 and 78.3% during winter).
The PAI results for the perennial species S. cumini and M. indica
were 87.8 and 85%, respectively. These trees are characterized by
a dense canopy, a plagiotropic trunk, and produce relatively large
tree coverage. This leads to high cooling effects in terms of thermal
comfort, especially during the winter. The attenuation results for
solar radiation during the summer were 87.2 and 89.2%, and 89.1
and 88.6% during winter for S. cumini and M. indica, respectively.
Semi-deciduous species as J. mimosaefolia, L. glyptocarpa and C.
pluviosa can be characterized by their plagiotropic trunk, distinct
canopies, and considerable variation in PAI (26.9, 74.8, and 92.3%
respectively), which can vary from sparse to dense during the year.
These native trees have a medium–large coverage and high cooling
effects in terms of thermal comfort, especially during summer, due
to the quality of shading and access by wind. As an example, C.
pluviosa can attenuate solar radiation by 83.8% in summer, but only
69.5% during winter.
Deciduous species such as Handroanthus chrysotrichus, S. campanulata and T. tipu are characterized by variation of leaves in
the crown over a year. Native Handroanthus chrysotrichus, with an
orthotropic sympodial trunk, has a PAI of 47.7% and attenuation of
solar radiation is 82.8% in summer and 46.4% in winter. When leafless, this value drops to 51.4%. Exotic species (S. campanulata and T.
tipu) are characterized by plagiotropic trunks, with PAIs of 78.1 and
72.2%, respectively. Attenuation of solar radiation during summer
was 76.3%, and over winter this was 55%.
For clusters of trees, the PAI results for C. pluviosa, L. glyptocarpa,
S. campanulata, T. tipu, D. indica and S. siamea were 99.3, 65.7, 77.5,
98.8 and 91.3%, respectively. During the summer, the results of solar
radiation attenuation for C. pluviosa, T. tipu, D. indica and S. siamea
were 94.8, 80.2, 73.5 and 89.2%, respectively. During winter, solar
radiation attenuation results for C. pluviosa, L. glyptocarpa, S. campanulata and D. indica were 92.5, 76, 82.4, and 72.3%, respectively.
Clusters of C. pluviosa had the best cooling effects for thermal comfort. This can be explained by specific features of this species: they
are large trees with maximal coverage due to their height; they
have plagiotropic trunks; and small bipinate leaves. In addition,
the distance between the trees was proportional to the diameter
of the crown (10 m × 10 m), along with the number of trees in the
cluster (n = 20), and the linear formation of the cluster contributed
to our findings.
4. Estimating cooling effects based on trees features
The tridimensional model was based on tree features including height, crown radius, trunk length and diameter, and outdoor
disposition. Meteorological data from 2003 to 2010 were used to
quantify the contribution of trees’ shade on built-up spaces using
PET.
The results (Fig. 8) show that individual trees as M. indica, S.
campanulata, L. glyptocarpa, S. cumini, C. pluviosa provided the best
results with respect to improvements in thermal comfort. These
trees resulted in a reduction of air temperature of 5.5–7.4 ◦ C from
10:00 AM to 2:00 PM. Individual trees as P. coulteri and P. palustris exhibited the worst results in terms of cooling effects, with the
air temperature reduced by only 0.8–4.0 ◦ C over the same period.
A cluster of S. siamea, C. pluviosa and T. tipu trees had the best
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Table 2
Differences between results in the shade and in the sun.
Trees species
Disposition
Season
Differences of air
temperature (◦ C) in the
sun and in the shade
during 10 AM–2 PM
Differences of PET (◦ ) in
the sun and in the
shade during 10 AM–2
PM
Solar radiation
attenuated (%)
Plant area
index (PAI)
SVF
Pinus palustres
Individual
0.66
Individual
47.7%
0.52
Jacaranda mimosaefolia
Syzygium cumini
Individual
Individual
26.9%
87.8%
0.73
0.12
Mangifera indica
Individual
85.0%
0.15
Caesalpinia pluviosa
Individual
79.7
69.8
83.8
78.3
82.8
46.4
51.4
63.8
87.2
89.1
89.2
88.6
83.8
69.5
94.8
92.5
63.9
76.0
55.0
82.4
76.2
80.2
73.5
72.3
89.2
34%
Handroanthus
chrysotrichus
7.2–9.9
4.6–9.1
7.1–9.5
6.6–9.3
11.2–14.2
0.6–1.2
2.6–3.6
4.1–11.7
10.8–13.9
7.5–10.8
9.4–12.7
13.0–17.5
12.3–16.0
7.4–11.0
12.5–14.3
7.8–10.5
8.1–16.0
8.8–14.5
4.1–9.1
0.9–2.6
9.8–12.8
11.3–13.5
0.6–2.7
0.3–1.2
0–0.5
0.53
Individual
0.5–1.3
0.1–1.0
0.6–1.1
0.8–0.9
1.6–1.8
0.3–0.7
0.1–0.2
0.3–1.3
1.5–2.8
1.9–2.6
1.0–1.2
0.9–1.1
0.9–1.3
2.2–2.7
0.9–1.3
0.1–2.0
0.1–0.8
0.2–1.1
0.3–1.4
1.0–2.5
1.0–1.8
0.2–2.0
0.2–0.7
0.7–1.8
0.1–0.7
47%
Pinus coulteri
Summer
Winter
Summer
Winter
Summer
Winter (leafless)
Winter (with flowers)
Winter
Summer
Winter
Summer
Winter
Summer
Winter
Summer
Winter
Winter
Winter
Winter
Winter
Summer
Summer
Summer
Winter
Summer
92.3%
0.07
0.01
Cluster
Lafoensia glyptocarpa
Delonix indica
Individual
Cluster
Individual
Cluster
Individual
Cluster
Cluster
Senna siamea
Cluster
Spathodea campanulata
Tipuana tipu
cooling effects, with their shading reducing the air temperature by
5.9–11.5 ◦ C. These results demonstrate that clusters of trees can
mitigate temperatures to a greater extent compared with individual trees. As well, the planting design of clusters trees with 2
lines and 5–10 trees in each line can provide more thermal comfort than others analyzed. Tree height, canopy size, and shape
are features that likely influence the improvement of the thermal
environment.
99.3%
74.8%
65.7%
78.1%
77.5%
72.2%
98.8%
91.3%
0.25
0.34
0.21
0.22
0.27
0.012
0.08
83.4%
0.16
5. Discussion
Thermal bioclimate analysis with respect to air temperature,
Tmrt , and PET, for Campinas, Brazil, was able to describe climate
change due to solar radiation attenuated by the shade of trees
(Abreu-Harbich et al., 2013a). However, the behavior of arboreal
species is affected by differences in growth conditions and tree
features (Abreu-Harbich et al., 2012; Bueno-Bartholomei & Labaki,
Fig. 7. Comparison between plant area index and solar radiation attenuated by trees.
L.V. de Abreu-Harbich et al. / Landscape and Urban Planning 138 (2015) 99–109
107
Fig. 8. Diurnal courses of physiologically equivalent temperature (PET) (◦ C) for different for single trees and clusters of trees.
2003; Correa et al., 2012; Shahidan et al., 2010; Shashua-Bar et al.,
2010).
Air temperature reductions are 0–2.8 ◦ C for single trees and
0.3–15.7 ◦ C for clusters of trees during the day (10:00 AM to 2:00
PM) during the study period. The results of the PET are 0.84 to
17.5 ◦ C for single trees and 0.3 to 15.7 ◦ C for clusters of trees for
the same period. Most studies of vegetation influences in urban
microclimate have been focused in mitigation of air temperatures
(Akbari, 2002; Bueno-Bartholomei & Labaki, 2003; Santamouris,
2001; Scudo, 2002; Shahidan et al., 2010; Shashua-Bar et al., 2010)
instead of PET and Tmrt . The quantification of tree shading benefits,
in terms of PET, provides an accurate measure of the real cooling
effects for thermal comfort.
Comparing the results from single trees and clusters of trees,
air temperatures for individual C. pluviosa and T. tipu were about
one third that of clusters. The PET results we obtained were similar.
Our findings suggest that clusters of trees, in different proportions,
function like a microclimate thermoregulator. The large coverage
provided by clusters of trees is able to mitigate PET through an
umbrella effect (Emmanuel, 2005).
Our results suggest that cooling effects are influenced by the permeability of the crown (Shahidan et al., 2010; Shashua-Bar et al.,
2010), and the capacity of shading in attenuating solar radiation
(Abreu-Harbich et al., 2012; Bueno-Bartholomei & Labaki, 2003).
If the maximum mean temperatures of PET during the months of
May to September are 29 ◦ C (Abreu-Harbich et al., 2013a, 2013b),
trees that can reduce the PET by greater than 15 ◦ C in the winter, such as M. indica, could provide thermal discomfort. These
findings confirm the results of Emmanuel (2005) and Lin et al.
(2010).
Tree features such as tree height, green coverage, shape and
permeability of the crown can influence the thermal environment,
and their effects on microclimates could be observed through simulation. The field measurements suggest that trunk and branching
structure, and size and shape of leaves contribute to cooling effects.
C. pluviosa is tall, has large coverage, an elliptical crown, a plagiotropic trunk, and small leaves that are bipinate and linear. These
features cannot be simulated on RayMan Pro.
In outdoor spaces, urban greenery is able to control and improve
thermal comfort, and mitigate air temperatures. For indoor areas,
tree shading can reduce the incidence of solar radiation on building
facades, improve thermal comfort, conserve energy spent on refrigeration, and maintain a healthy environment (Emmanuel, 2005;
Emmanuel et al., 2007; McPherson et al., 1994; Santamouris, 2001).
The shape and size of trees can modify the effect in different climate
regions (Shashua-Bar et al., 2010; Streiling & Matzarakis, 2003).
The evaluation of different commonly found arboreal species and
their characteristics should be taken into account by professionals of the urban built environment. This would improve outdoor
thermal comfort, reducing the effect of heat islands and ensuring a
better quality of life for people in the urban environment (AbreuHarbich et al., 2013b; Correa et al., 2012; Shashua-Bar et al., 2010;
Streiling & Matzarakis, 2003).
6. Conclusions
From our findings it can be seen that the main influencing
parameter in the microclimate and urban environment is mostly
driven and controlled by changes in the Tmrt and wind speed, especially in tropical cities. The size and shape of the tree crown can
improve thermal comfort in a microclimate, as can the size and
shape of the leaves, the trunk, and the permeability of the crown.
The semi-deciduous C. pluviosa exhibited the best results in terms
of PET for both individual and clustered formations. These particular trees have small bipinate linear leaves, plagiotropic trunks,
large green coverage, and moderate crown permeability. The crown
architecture for these trees promotes large green coverage that
filter solar radiation in accordance with the prevailing season,
and allow for the wind to permeate. The phenology of trees also
needs to be considered. The shade of native species (Handroanthus
chrysotrichus and C. pluviosa) which vary during all the year can be
used for human thermal comfort adaptation.
Clusters of trees can increase the cooling effects of one tree;
however, it is important to note how tree formation can promote
a large area of shade, especially for aligned clusters. For effective
tree shading along a street, the distance between trees needs to be
108
L.V. de Abreu-Harbich et al. / Landscape and Urban Planning 138 (2015) 99–109
relative to the diameter of the crown. Further studies can quantify
the thermal comfort provided by different species of trees planted
in streets and open areas and the influence’s distances of these
green areas in tropical cities. The optimal distribution of single
trees, or clusters, to produce shading during the harshest conditions is the main driver for improving human thermal comfort.
Besides thermal comfort, the ecological factor, economic, cultural,
and aesthetic aspects of urban planning must be considered.
Planning needs to be appropriate for recent climate conditions
and future climate changes. Planting the appropriate trees around
the buildings, in sidewalks, pedestrian ways, squares and parks
can be helpful fighting climate change in micro scale. Evaluation
of different arboreal species commonly found, and tree-planting
strategies during the urbanization of cities, is important information for urban planning and maintaining an urban microclimate.
Additionally, tree planting with typical regional trees providing
mostly shade (C. pluviosa) is a practical and inexpensive solution,
and is considered as an energy efficient alternative.
Acknowledgements
This research was supported by São Paulo Research Foundation (FAPESP) research grant (08/05870-5), National Counsel of
Technological and Scientific Development (CNPq) research grant
(311641/2013-0), and research cooperation between Coordination
for the Improvement of Higher Education Personnel (CAPES) and
German Academic Exchange Service (DAAD) research grant (BEX
4234/10-3).
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.landurbplan.
2015.02.008.
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