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Temperature Reduction Effects of Rooftop Garden Arrangements: A Case Study of Seoul National University


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Increasing urbanization has highlighted the need for more green spaces in built-up areas, with considerable attention of vertical installations such as green walls and rooftop gardens. This study hypothesizes that the rooftop-garden-induced temperature reduction effects vary depending on the type of arrangements. Therefore, the objective of this study is to find the most efficient arrangement of the roof gardens for temperature reduction. This paper presents the results of a quantitative analysis of the temperature reduction effect of rooftop gardens installed on structures and sites on the campus of Seoul National University. An ENVI-Met simulation is utilized to analyze the effects of roads, buildings, green areas, and vacant land on temperature and humidity. The effects of the following five rooftop garden configurations were compared: extreme, linear (longitudinal), linear (transverse), checkerboard, and unrealized rooftop gardens. The extreme and linear (longitudinal) gardens achieved the maximum temperature reduction, −0.3 °C, while the lowest maximum reduction of −0.2 °C was achieved by the checkerboard pattern. Over larger areas, the greatest impact has been recorded in the mornings rather than in the afternoons. The results of this study will be useful for those planning and installing rooftop gardens at the district and city levels.
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Temperature Reduction Eects of Rooftop Garden
Arrangements: A Case Study of Seoul
National University
Jaekyoung Kim 1, Sang Yeob Lee 1and Junsuk Kang 1,2,3,4,*
1Department of Landscape Architecture and Rural Systems Engineering, Seoul National University,
Seoul 08826, Korea; (J.K.); (S.Y.L.)
2Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, Korea
3Interdisciplinary Program in Landscape Architecture, Seoul National University, Seoul 08826, Korea
4Interdisciplinary Program in Urban Design, Seoul National University, Seoul 08826, Korea
*Correspondence:; Tel.: +82-2-880-2227
Received: 9 June 2020; Accepted: 23 July 2020; Published: 27 July 2020
Increasing urbanization has highlighted the need for more green spaces in built-up areas,
with considerable attention of vertical installations such as green walls and rooftop gardens. This
study hypothesizes that the rooftop-garden-induced temperature reduction eects vary depending
on the type of arrangements. Therefore, the objective of this study is to find the most ecient
arrangement of the roof gardens for temperature reduction. This paper presents the results of a
quantitative analysis of the temperature reduction eect of rooftop gardens installed on structures and
sites on the campus of Seoul National University. An ENVI-Met simulation is utilized to analyze the
eects of roads, buildings, green areas, and vacant land on temperature and humidity. The eects of
the following five rooftop garden configurations were compared: extreme, linear (longitudinal), linear
(transverse), checkerboard, and unrealized rooftop gardens. The extreme and linear (longitudinal)
gardens achieved the maximum temperature reduction,
C, while the lowest maximum reduction
C was achieved by the checkerboard pattern. Over larger areas, the greatest impact has been
recorded in the mornings rather than in the afternoons. The results of this study will be useful for
those planning and installing rooftop gardens at the district and city levels.
Keywords: ENVI-met; heatwave; rooftop gardens; temperature; humidity; vertical green areas
1. Introduction
1.1. Background
The rapid growth in industrial and urban development has led to ongoing indiscriminate
urbanization in countries around the world, creating serious environmental problems, the destruction
of forests, and extreme air pollution [
]. Above all, global warming is becoming critical. Between
1880 and 2018, the temperature of the Earth’s surface increased by around 0.9
C [
]. The resulting
rise in global sea levels and the destruction of ecosystems that are unable to withstand these rising
temperatures will have a major impact on everyday life for billions of people [2,3]. By the end of this
century, the average temperature on Earth could rise by anything between 1.1
C to 6.4
C according to
an intergovernmental panel on climate change and the global average sea-level rise is forecast to be
somewhere between 0.4 m and 0.77 m, with every 0.1 m rise in global sea level directly aecting up to
10 million people [24]. Our growing awareness of this impending crisis is driving many researchers
to seek new ways to tackle global warming, including developing alternative energy sources to reduce
greenhouse gas emissions and new approaches that reduce energy consumption levels [
]. This
Sustainability 2020,12, 6032; doi:10.3390/su12156032
Sustainability 2020,12, 6032 2 of 17
is particularly important in densely populated built-up areas such as cities, where environmental
problems are most obvious [
]. Mitigating the heat island eect caused by artificial heat emissions
in urban areas could, thus, make a significant contribution; integrating garden areas such as parks
and street water features into urban environments could not only improve the standard of living of
inhabitants but also substantially reduce the impact of the city on global warming [
]. However, in the
case of the Seoul Metropolitan Government area, only about 34.9% of the surface area is currently
devoted to gardens and parks [
]. In other words, it is necessary to create a new type of green space
that can replace buildings and roads [7].
1.2. Purpose of This Study
One approach that is gaining widespread support is the aorestation of vertical space, with
gardens and vegetation no longer being limited to ground level installations [
]. By way of illustration,
options for integrating garden space into buildings and other man-made structures could be green
walls and roof gardens [
]. Unfortunately, green walls tend to be very sensitive to local environmental
conditions, limiting the kinds of plants that can be used and only certain types of structures are suitable
for wall aorestation [9]. Rooftop gardens are thus far more common than green walls, as they suer
from fewer restrictions [
]. So far, many studies have dealt with rooftop gardens. However, the
impact of rooftop gardens on the entire city or a wide area was not clearly understood, mainly by
analyzing only small-scale temperature reduction eects in one space [
]. The study began with
the hypothesis that the eect of temperature reduction, in a wide range of areas, changes with the
arrangements of rooftop gardens. Therefore, the purpose of this study is to learn how much the
temperature reduction eect is depending on the arrangement of rooftop gardens in a large area. This
study conducted a quantitative analysis of the temperature reduction eects of rooftop gardens on both
the structures hosting them and the surrounding area. ENVI-Met, a climate simulation software [
was adopted to derive optimal plans that maximize the temperature reduction eects achieved by each
type of rooftop gardens.
2. Literature Review
In a recent study [
], a green area policy proposal was made for future improvement of Taiwan’s
heat environment by using the ENVI-met program. It suggests that if the green area is increased to
more than 60%, the thermal environment can be improved. When the ratio of increasing green area was
fixed at 60%, there was a temperature reduction eect of at least
C, up to
C, depending on
the installation rate of the permeable pavement. The last prior research identifies the eect of urban
form and specific building functions on the thermal environment [
]. This study suggests that the
optimal size, height, and layout of buildings were presented in dierent ways. Therefore, a single index
is insucient to measure the direct relationship between the urban form and the thermal environment.
Roof gardens, which can be installed on existing residential, commercial, and industrial
buildings [
], provide the following three main types of benefits: (1) environmentally, (2) socially, and
(3) economically [
]. Their environmental eects go beyond simply reducing surface temperatures:
the plants absorb carbon dioxide and hence help to mitigate the urban heat island eect. Besides, they
often support the creation of garden spaces to help maintain a more diverse and resilient biological
ecosystem [
]. It has been documented that a 10-cm-deep soil layer can absorb 20–30 L of rainwater
in each m
, reducing the pressure on urban storm drains and helping to prevent flooding during
extreme rainfall events [
]. Social eects include a more attractive urban environment that enhances
inhabitants’ quality life and psychological stability [
]; on the roof of a building with a garden installed,
a 20 cm layer of soil has been shown to reduce ambient noise levels by as much as 46dB [
]. The
subsequent reduction in the amount of energy required to meet the building’s needs provides a further
economic incentive to encourage greater rooftop aorestation [
]. Although these three classes of
advantages are closely related to each other [
], this study focuses on the environmental eects,
quantitatively analyzing the temperature-reduction eects of roof gardens.
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Most of the research into the environmental impacts of roof gardens have focused on
temperature reduction. For example, a year-long study tracking the environmental impacts
(temperature/humidity/light) achieved by nine dierent types of flowers at building in Gyeonggi-do,
Korea, reported that before the roof garden was installed, the highest figures are as follows; at the
average atmospheric in July, at 34.4
C, the average relative humidity was September, at 59.3%, and
the illumination levels were in August, at 990,150 lux. All the flowers planted in the rooftop plots
successfully reduced the temperature, with the greatest temperature reduction being achieved by
the Blackberry Lily, Belamcanda chinensis, which was around 7.7
C lower than that recorded on the
comparison concrete plot [
]. Another study found that a temperature reduction of 5
C could be
achieved by the evaporation of soil moisture from bare soil, with no plant material presece [
]. In a
more recent study, bare soil plots were found to heat up and cool down relatively rapidly compared to
plots containing plants, probably because the plants had a higher heat conductivity than the soil [
This caused the temperature across the rooftop to vary by up to 2
C. The humidity varied from about
2.6 to 3.1%, indicating that a rooftop garden can indeed absorb solar energy that would otherwise pass
into the building below and thus reduce the load on the building’s air conditioning system.
Users’ psychological changes were compared and analyzed with the Profile of Mood States (POMS)
and Semantic Dierential Method (SDM) as they visited six dierent types of rooftop gardens [
]. In
another study, bamboo forests, ponds, and city areas were randomly arranged in an arboretum. Study
participants were asked to quietly appreciate the scenery in their assigned area for 10 min and then
walk through either the natural environments or the urban area for 15 min [
]. Their physiological
characteristics were measured before and after completing the task, revealing a statistically significant
improvement in those walking through the natural areas compared to those assigned to the urban
environment [25,26].
Several studies have analyzed the energy and economic savings achieved with the aid of dierent
types of rooftop garden systems, with most utilizing the Life Cycle Cost for the analysis. Overall, a
deep layer of sandy loam delivered the highest savings rate of heat energy, with reinforced insulation
material a close second. An energy-saving rate of around 10% per unit area was achieved for soil
depths of over 300 mm [2730].
The software, which is used in this study, is a three-dimensional climate analysis program that
quantifies the eects of environmental factors such as vegetation, buildings, and solar radiation [
Fur the more, the program can model the impact of gardens, fields, and building materials as well as
taking into account the airflow between and around buildings, evaporation, and the heat exchange
systems of surfaces [
]. ENVI-met has been used to analyze the urban thermal environment of the
city of Songdo [
] and the campus of Konkuk University [
]. Both of these studies involved only a
simple analysis.
3. Site Selection and Specifications
Two dierent sites were chosen for this study, both on the campus of Seoul National University in
Gwanak-gu, Seoul. In addition to their proximity to the weather station on Mt. Gwanak, where the
weather data was collected, their distinctly dierent characteristics provide a good test of the model.
The reason for selecting the aforementioned sites is that two sites are easily accessible, and a lot of
geographical information is provided from the Seoul Metropolitan Government and Seoul National
University. The first site, Seoul National University Engineering college is a public facility, so all the
rooftop entrances are open. Therefore, it is easy to measure the environmental data such as temperature
and humidity of the site and to analyze the target site. In the case of Seoul National University Station,
it is easy to obtain building information, sea level, height, land use, and soil conditions of site by using
the three-dimensional spatial information system provided by the Seoul Metropolitan Government.
The first study site is an area around the Engineering College of Seoul National University located
in the south of Gwanak-gu in Seoul (Figure 1). The campus is located in a mountainous area, with Mt.
Cheongnyongsan to the north, Mt. Dolsan to the west, and Mt. Gwanak to the east. The lowest site at
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Seoul National University is 58.0 m above sea level, and the highest is 189.3 m. Within the first analysis
site, the lowest altitude of the sea level is 114 m and the highest altitude is 140 m.
Figure 1. The first study site (Seoul National University, Seoul, Korea).
The slope of the highest and lowest points was 7.9%, and the total area of this site is 200,000 m
500 m). The site consists of university buildings, roads, and mountains, and 51% of the site was
used as buildings. The number of buildings is 24 in total, and the buildings are partially connected
through a passageway. The height of the tallest building is 28.8 m while that of the lowest one is 11.2 m.
Accordingly, the average height of the buildings is 19.2 m. All buildings used for research or lecture
purposes were of reinforced concrete type. The roads have occupied 19% of the site area, while the rest
of the region specified to the green areas, gardens, and parking lots [38].
The second study site is an intersection at a Seoul National University Station in Gwanak-gu,
Seoul Metropolitan Government (Figure 2). The Seoul National University station is located in
Bongcheon-dong, the center of Gwanak-gu. The site area is 250,000 m
(500 m
500 m) and consists
of 450 commercial buildings and 311 residential buildings. The second site consists of a total of 761
buildings. The lowest altitude in the site was 32.0 m, and the highest one was 38.7. The overall slope
was less than 2% and 72% of areas were buildings, 21 of roads, and the rest of the area accounted
for parks and parking lots. The tallest building has 73.9 m in height, while the shortest one acquired
height of 6.5 m, and the average height of buildings is 28.2 m [
]. For this study, the analysis was
conducted for the 24 h when Gwanak-gu experienced its highest temperature of the year, midnight to
midnight, on 5 August 2019.
Figure 2. The second study site—a major intersection at an outstation of Seoul National University.
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4. Methods of Design and Simulation
Once appropriate study sites had been selected, the local temperature, humidity, and wind speed
data provided by the Korea Meteorological Administration were collected, and the target locations
were modeled. Information on building heights from the National Geographic Information Institute’s
spatial information portal was converted to a format compatible with ENVI-met using Rhino 6 and the
Grasshopper and Dragonfly plug-ins [
]. The second step has been related to utilizing the information
collected to conduct the simulation analysis. Finally, the new model was applied to develop an optimal
design for rooftop gardens in the study areas.
4.1. Site Design and Data Analysis
A polyline file provided by the National Geographic Information Institute was utilized for this
research. Figure 3shows the terrain and buildings depicted using the realistic modeling program
Rhino 6. Two plug-in modules, Grasshopper and Dragonfly, were then used to convert the Rhino 6
data into a format suitable for ENVI-Met.
Figure 3.
Model data for the Rhino 6 analysis and Grasshopper code. (
) Numerical map and modeling
top view; (b) modeling perspective view.
The modeling data were transferred to ENVI-Met Space using Grasshopper codes. ENVI-Met
inputs include buildings, topography, soil, vegetation, and receptors. The materials of the building
were set up as reinforced concrete, and asphalt was set for land pavement. GIS topography files were
also used for modeling. The lattice spacing was 5 m along all three axes; the vertical analysis extended
to a height of 300 m. The corresponding modeling data for Site 1, the Seoul National University
Campus are depicted in Figure 4, and modeling data for site 2, the Seoul National University Outstation
is illustrated in Figure 5.
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Figure 4.
Model data for Site 1. (
) Building data; (
) soil data (roads and land); (
) 3D modelling data.
Figure 5.
Model data for Site 2. (
) Building and vegetation data; (
) soil data (roads and land); (
) 3D
modelling data.
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4.2. Model Simulation
The two sites’ temperature-reduction analysis utilized two ENVI-Met components—ENVIGuide
and Leonardo—to convert the site models created by Rhino and Grasshopper into appropriate
ENVI-Met formats. Information on the various environmental factors, times of the day, time intervals,
and location characteristics were entered and the simulation performed with ENVIGuide. The resulting
files presented in the output data were then sent to Leonardo to analyze the weather conditions
throughout the day. All research results, including existing modeling analyses, were analyzed based
on the ongoing simulations [39].
Existing modeling analyses were used as controls for all other analyses; apart from the presence
or absence of a rooftop garden, the timing, time intervals, and environment variables remained the
same for all the simulations. The simulation was run for the 6 h from 09:00 to 15:00 on 5 August 2019,
with data extracted at hourly intervals. In the case of environmental analysis, the basic Beginner Level
was selected and simulated for general data. The temperature range was set between 22
C and 34
to reflect the temperature of a hot day. Besides, the wind speed and direction were set at an average
of 1 m/s and toward the east with the direction angle between 80 and 100 degrees, respectively. To
evaluate the potential eectiveness of the various types of rooftop gardens, simulations of the existing
situation and the temperatures with gardens installed on all the available rooftops were performed.
This type of comparison is supported by ENVI-Met’s Leonardo program.
Five rooftop garden configurations were analyzed for this study (Table 1). The impact of changes
in various environmental factors on the host structure itself and the surrounding area for each
configuration was modeled using ENVI-Met and an optimal plan derived [
]. The five types were:
an extreme rooftop garden, linear (longitudinal) and linear (transverse) gardens, a checkerboard
pattern, and an unrealized (bare rooftop) garden. In Korea, where there is a predominant wind
direction, the results obtained would be expected to dier when the roof-top aorestation is aligned in
dierent directions.
Table 1. The five rooftop garden configurations tested.
Extreme Rooftop
(Transverse) Check Patterned Unrealized
Rooftop Garden
5. Results and Discussion
5.1. Existing Model Analysis
5.1.1. Simulated Data
The results analyzed by employing the Leonardo program were derived in the form of a series of
2D maps with the maps generated at 5 m vertical intervals as shown in Figure 6.
The altitude at which the best observation of the temperature distribution could be achieved
was 122.5 m. Figure 6shows the data for 12:00 from the existing modeling data. The minimum and
maximum temperatures are 27.5
C and 27.9
C, respectively. The distribution of temperature varies
with respect to the location of the building as the wind direction has been fixed in one direction only.
By shielding the building from the hot winds of the heatwave period, one can assume that the west
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part of the building has a low temperature. Winds shielded by buildings in the longitudinal direction
will then have winds in the northeast and southeast, respectively.
Figure 6.
Simulated data at 12:00 in the Target Site. (
) Seoul National University (temperature on
5 August); (b) National University Station (temperature on 5 August).
From Figure 6b illustrating the simulation data at 15:00, it was found that the minimum and
maximum temperatures were 28.1
C and 33.2
C, respectively. Considering the location of the building,
it can be inferred that the northeastern part of the site subjected to a low temperature due to shielding
the building from extreme heat.
5.1.2. Analysis Results by Time Zone
The results of the site1 model analysis by time zone are shown in Figure 7.
Figure 7.
Time zone simulation data before modeling the rooftop garden (Site 1). (10, 11, 12 (
13, 14, 15 (below).)
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From Figure 7, it can be cathed out that the temperature gradually increased from 10:00 to 15:00,
and the distribution of temperature, excluding buildings, varied in the shape from time to time. The
distribution of the y-axis at 12:00 between 130 m and 270 m and the x-axis at 13:00 tend to have a
temperature distribution that varies with wind direction. Meanwhile, the temperature distribution of
point at 12:00 is 0.5
C higher than the surrounding area. This is the result of a concentration of air
shielded by buildings all over the place.
The analysis results for the models of site 2, by time zone, are shown in Figure 8.
Figure 8.
Time zone simulation data before modelling rooftop garden (site 2) (4, 8, 12 (
), 16, 20,
24 (below)).
From the results, it was revealed that changes in temperature by time zone were mostly aected
by the location of the sun. Temperatures, before sunrise, acquired almost a concrete amount about
C until 08:00, while a sharp increase in temperature was observed after sunrise. Also, for
temperature distribution within each time zone, the temperature dierence between the region in the
northeast and the southwest was assumed relatively small due to the eects of altitude and wind
direction. On the other hand, the comparison of the analysis data between 4 h and 24 h indicates that
the temperature decrease is less than the temperature increase, which is assumed to be the result of the
slow-decreasing properties of asphalt. This is because the range of temperature changes on roads set
as asphalt, through the time, was smaller. The daily maximum temperature was 33.2
C at 15:00, and
the maximum temperature dierence was about 5.3 C at 14:00.
5.2. Results of the Analysis on the Eciency of Rooftop Aorestation by Time Zone
To analyze the eects of temperature reduction of the rooftop garden through the time, the
simulations of the existing model and the model carried out at the rooftop garden of all buildings were
compared. The simulation results revealed the reduced temperature and areas by time zone (Figure 9).
The comparison was made except for areas which reduced the temperature by 0.03
C. When the
roof garden was created, the most eective times were 10:00 and 11:00. Referring to Figure 9, from
12:00 to 15:00 the reduction temperature and the shape of the area were similar.
The maximum temperature reduction and the frequency of reduction over time are shown in
Figure 10. The maximum temperature reduction at 10 a.m. was
C and that of 11:00 was
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which significantly reduced compared to other times. The frequency was also 42.1% at 10:00 and 38.0%
at 11:00, which can be said to have been aected by the temperature reduction.
Figure 9.
Analysis of temperature reduction eect of roof garden by time zone at Seoul National
University (10, 11, 12 (above), 13 14 15 (below)).
Figure 10.
Maximum temperature reduction and frequency of reduction of rooftop garden by time
zone at Seoul National University.
In the case of roof garden by time zone, the dierence between the simulation of the existing
model and the simulation of the greening at all rooftops was analyzed and the reduced temperature
and area were compared by time zone (Figure 11). In the case of having the gardens installed at all
the rooftops, most areas experienced a temperature reduction of about 1
C. It was observed that the
temperature reduction diered over time. For instance, at 00:00–09:00, only the temperature in the
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rooftop garden area was reduced. However, at 11:00–17:00, the temperature reduced near the areas
where the roadside trees were planted. It might have resulted from the increased transpiration of
plants with strong sunlight and lower humidity. It was seen that the temperature reduction was low
on 5 August due to high humidity from 00:00–09:00. It was also observed that after 18:00, areas with
reduced temperatures were near the rooftop, before which temperatures were reduced only on roads,
not near buildings.
Figure 11.
Analysis of roof garden-induced temperature reduction by time zone at Seoul National
University Station (6, 12 (above), 18, 24 (below)).
The variation of the maximum temperature reduction with respect to the time zone is shown in
Figure 12. At all times, the maximum temperature reduction was 6
C or higher, of which the maximum
temperature reduction occurred at 15 o’clock and 12.9
C. This is assumed to be the area in which the
elevation dierence occurred in ENVI-Met Space or the area in which the horizontal number exists.
Figure 12.
Maximum temperature reduction and variation of reduction of rooftop garden by time zone
at Seoul National University Station.
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5.3. Results of the Analysis on the Eciency of Rooftop Aorestation by Type
Modeling of Target Sites by Aorestation
Modeling was made in dierent ways depending on the type of roof-top garden of each type. The
area covered by the rooftop garden is shown in green (Tables 2and 3).
Table 2. Target location model by type of rooftop garden at Seoul National University.
Extreme Rooftop
(Transverse) Check Patterned Non-Rooftop
Table 3.
Target location model considering type of rooftop garden at Seoul National University Station.
Extreme Rooftop
(Transverse) Check Patterned Non-Rooftop
Figure 13 shows the results of the temperature-reduction analysis by the rooftop type. Depending
on the location and degree of rooftop green, the extent to which temperature distribution is aected was
subtly dierent (extreme rooftop garden type). In the case of a fully aorestation type, both the west
side of the building site decreased in temperature. On the other hand, in the case of linear (longitudinal)
less space than the full-green type was aected by temperature reduction, and the lower-temperature
range was greatly distributed to the west. Meanwhile, the linear (transverse) type was significantly
lower in temperature than the other three types and the aected area was also transverse-shaped for
both cases. The check pattern type was generally an area aected by the west side of the building site,
but unlike fully aorestation, linear (longitudinal), an area with very little temperature reduction was
located between the building and the building.
The simulation data for each arrangement were compared with data when the rooftop garden
was not installed. In particular, when comparing point
to point
shown in Figure 13, the dierence
in temperature reduction eect can be clearly seen for each type of rooftop garden. This is attributed
to the location of the building, and the results shown in Figure 13 are due to the unique shape of the
building, where several layers of the building are connected at dierent heights. In extreme rooftop
garden type, the northern part of the building was aected by the temperature reduced. In the linear
(longitudinal) direction, the center of 39 dong building was aected by the temperature reduced. In the
check pattern type, the only northeastern part of the building was aected by the temperature reduced,
and in the linear (transverse direction), no area was aected by the temperature decrease.
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Figure 13.
Temperature-reduction analysis by rooftop type—extreme green rooftop, linear (longitudinal),
(above)/linear (transverse) check pattern type, (below).
For the analyzed time zone, data from the 15:00 time zone, which had the greatest eect on
reducing the temperature of the rooftop garden, was utilized among the time zones of the previous
study results. Two of the four types of temperature reduction, extreme rooftop green and linear
(longitudinal), were found to be about 0.1
C higher than other types on average. In the case of
complete gardening and linearity (longitudinal), the extent to which temperature distribution was
aected was subtly dierent depending on the location and degree of the roof garden. In the case of a
complete green area, the temperature of buildings located on the edge of the target site had further
reduction. On the other hand, linearity (longitudinal direction) had a greater eect on the building’s
surroundings compared to the full-roof garden type, and the temperature in the center of the target
area showed more decrease (Figure 14).
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Figure 14.
Plotted data corresponding to 15:00 linear (longitudinal) temperature reduction eect result
(left)/linear (longitudinal) extreme rooftop temperature reduction dierence (right).
The maximum temperature reduced for each type is shown in Table 4.
Table 4. Maximum temperature reduction eect by type and time zone (unit: C).
Time Type A Type B Type C Type D
Seoul National
10:00 0.32 0.32 0.28 0.22
11:00 0.27 0.27 0.23 0.19
12:00 0.27 0.26 0.21 0.18
13:00 0.24 0.23 0.18 0.17
14:00 0.18 0.17 0.15 0.14
15:00 0.22 0.21 0.20 0.17
Seoul National
10:00 0.67 0.63 0.43 0.41
11:00 0.76 0.74 0.51 0.46
12:00 0.77 0.75 0.61 0.57
13:00 0.68 0.66 0.58 0.51
14:00 0.70 0.67 0.53 0.56
15:00 0.89 0.88 0.66 0.68
Type A means extreme rooftop, Type B refers to longitudinal linear rooftop, Type C means transverse rooftop
greening, and Type D means check patterned rooftop.
From Table 4, it can be realized that the maximum temperature reduction of the full-aorestation
type and linear (longitudinal) was
C, while the type with the minimum amount was
C in a
check-patterned format. On the other hand, for the linear (transverse) type, the area of temperature
reduction was lower than the other three types, but the maximum temperature reduction was
which had more decrease than the check pattern type owing to the parallel building sites on the x-axis
0–150 m and the y-axis 320–450 m.
6. Concluding Remarks
This study analyzed the weather conditions on the engineering area of Seoul National University’s
campus via an ENVI-Met analysis simulation to simulate the temperature reduction achieved by
five dierent rooftop garden configurations. The temperature in the target area is, not surprisingly,
aected by environmental factors such as wind direction and wind speed. The results of the simulation
conducted during the three hours either side of noon (09:00–15:00) on the hottest day of the year
(5 August 2019) showed that the overall temperature at the target site increased as time went on and
the temperature on the western side of the buildings, which was sheltered from the prevailing wind,
was lower than that on the eastern side.
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The examination of the temperature reduction eect achieved by rooftop gardens showed that the
gardens successfully reduced the temperature across a wider area in the morning than in the afternoon.
In the morning, about 39% and more of the total area experienced a reduction in temperature compared
to the afternoon, and the temperature decreased by more than 0.3% C. This is likely the result of
less photosynthesis in the morning than in the afternoon, but further work is needed to understand
the underlying mechanism and it is also necessary to explore the eects of dierent types of roofing
material at night when dew is deposited. This research examined only a short six-hour period in
summer; the temperature reduction eects of rooftop gardening deserve a much longer-period study
tracking the eects over multiple days or a year-long analysis over all four seasons.
Based on the analysis of the temperature reduction eect by type of rooftop garden, extreme rooftop
garden planting was the most eective type in terms of the area, delivering the greatest reduction of
temperature. The two linear configurations, transverse and longitudinal plantings, exhibited major
dierences. Despite the rooftops of the buildings in the target area were mostly rectangular and
having many dierent types of rooftops commonly encountered in urban neighborhoods, further
research is needed in a more diverse urban area. The target sites covered in this study had significant
temperature reduction eects of the Linear (Longitudinal) type. This is dierent from other studies.
Other studies expressed that more than 60 percent of green space will have a temperature reduction
eect [
]. However, the results revealed in this study can produce a large temperature reduction eect
if the arrangement is concerned, even if approximately 50% of the rooftop green space is secured.
This study has made two major contributions to research into developing more ecient plans for
wide-area-unit rooftop gardens. First, there are economic eects due to the quantitative identification
of temperature-reduction eects across a wider area that will reduce the energy cost incurred by
air-conditioning buildings during heatwaves; further research could examine the associated impact
on resource circulation, including water resources. Second, the environmental eects suggest rooftop
gardens may contribute to eorts to address the urban heat island phenomenon, providing a theoretical
basis for the assessment of the potential utility of increasing the vertical garden area around the site.
This study can make policy suggestions related to the installation of rooftop gardens. It can
have the greatest eect if a rooftop garden is installed in all buildings. However, if the construction
costs are insucient, an arrangement of rooftop gardens should be set in consideration of the wind
direction. In other words, it is deemed necessary to install a linear (longitudinal) rooftop garden that is
perpendicular to the direction of the wind.
However, the study was based on the simulation without collecting historical climate data for
both target sites. Therefore, future study will require at least one to two years of detailed temperature
information to ensure the justification for the selection of the target site.
Author Contributions:
J.K. (Junsuk Kang) designed and coordinated the study. J.K. (Jaekyoung Kim) and S.Y.L.
performed the analytical and conceptual study under the supervision of J.K. (Junsuk Kang). J.K. (Junsuk Kang)
reviewed the results of this study, and all authors have written and revised the text of this paper. All authors have
read and agreed to the published version of the manuscript.
This work is supported by Smart City R&D project of the Korea Agency for Infrastructure Technology
Advancement (KAIA) grant funded by the Ministry of Land, Infrastructure and Transport (20NSPS-B154565-03)
and the 10th Creative Research Program of the College of Agricultural and science at Seoul National University.
Conflicts of Interest: The authors declare no conflict of interest.
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... In this study, Ta, Tmrt, RH, and WS were the most frequently used meteorological variables to evaluate the outdoor thermal environment because they can directly reflect microclimate changes [108]. As the most familiar and basic meteorological variable, Ta was selected by almost all studies (70, 88.61%), and 11 studies used Ta as the only analytical variable [54,61,65,75,106,116,118,123,[139][140][141]. However, Rahul et al. [28] reported that using only Ta was insufficient for thermal stress investigation. ...
... The vegetation coverage ratio had a positive correlation with cooling performance. Kim et al. [140] surmised that installing green roofs in all buildings can have the greatest thermal effect at the city scale. Zhang et al. [75] reported that cooling performance might reach a threshold at a given coverage ratio which was determined to be 75%. ...
Urban green and blue infrastructures (GBI) are considered an effective tool for mitigating urban heat stress and improving human thermal comfort. Many studies have investigated the thermal effects of main GBI types, including trees, green roofs, vertical greenings, and water bodies. Their physical characteristics, planting designs, and the surrounding urban-fabric traits may impact the resultant thermal effects. ENVI-met, a holistic three-dimensional modeling software which can simulate the outdoor microclimate in high resolution, has become a principal GBI research tool. Using this tool, the GBI studies follow a three-step research workflow, i.e., modeling, validation, and scenario simulation. For providing a systematic and synoptic evaluation of the extant research workflow, a comprehensive review was conducted on GBI-targeted studies enlisting ENVI-met as the primary tool. The findings of 79 peer-reviewed studies were analyzed and synthesised for their modeling, validation, and scenario simulation process. Special attention was paid to scrutinising their data sources, evaluating indicator selection, examining main analytical approaches, and distilling recommendations to improve the research workflow. This review provides researchers with an overview of the ENVI-met methodology and recommendations to refine research on GBI thermal effects.
... If this phenomenon persists, it will promote thermal stress among urban residents, resulting in discomfort, as well as an increase in the mortality rates among the elderly and urban poor [6,7]. As urban areas continue to expand as the population increases, the UHI effect is accelerating; accordingly, research is being conducted to quantify and improve urban thermal environments [8][9][10][11][12][13][14]. ...
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Green roofs are implemented to reduce the urban heat island effect; however, studies are limited to comparing the reduction in urban heat island effect before and after implementation, and the focus is on the structural stability of the building rather than urban heat island reduction. In this study, using the sky view factor (SVF) in ENVI-met, a 3D microclimate modeling program, urban spaces were classified as closed, semi-open, and open areas. Meanwhile, the green roof types were subdivided according to the vegetation coverage rates, which included grass, shrubs, and trees. The vegetation ratio was evaluated using ENVI-met to determine which of the 10 scenarios was most effective for each urban space. The thermal environment was most comfortable in semi-open areas. Therefore, the green roof scenario with 70% grass and 30% trees was effective in closed areas, 50% shrubs and 50% trees were best in semi-open areas, and 70% grass with 30% trees, or 30% grass and 70% trees, was best in open areas. This study provides a basis for creating green roof guidelines aimed at improving the urban thermal environment, as well as creating other green infrastructure elements in cities.
... Amman, Jordan Kim et al. (2020) Increasing urbanization generates the environmental and aesthetic needs for more green spaces in built-up areas. In this regard, empirical evidence show that temperature reduction effect can be achieved by constructing rooftop gardens -they successfully reduced the temperature of the engineering area of Seoul National University's campus. ...
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Although agriculture has significantly evolved over the last decades, it is still adapting to the circular, innovative and digital economy; to the upsurge of modern agricultural technologies and to the imminence of environmental greening, especially in the European Union. The links involved in global agri-food value chain are transitioning from being economically competitive to being economically competitive and sustainable. The importance of greening the global agri-food chains along all of its links is instilled in the 2030 Agenda for Sustainable Development, the European Green Deal, the 2030 Climate Target Plan. In this context, the objective of this research was to design a circular agricultural system in the urban environment, and, more specifically, a solution for managing multidimensional complex issues, right in the campus of the Bucharest University of Economic Studies. A bibliometric analysis was elaborated with the purpose of identifying the favorable context and opportunity for implementing such a solution, grounded in the principles of urban agriculture. The result of this study consists of the authors' envisioned 'agro-urban' ecosystem; more specifically, an urban rooftop community garden that responds to challenges such as: limited resources (water, soil, labor force), unfavorable environmental conditions (specific to urbanization) and others. The proposed model is easily replicable and facilitates the transition to a cleaner, greener, circular economy.
... They are cost effective, easy to maintain, give high thermal advantage and high-water performance, while keeping the overall weight of the roof low. (Jaekyoung Kim, 2020) The study conducted on Seoul National University's campus via an ENVI-Met analysis simulation concluded that a temperature reduction of was 0.3•C was observed for a fully afforested (extensive roof) while a temperature difference of 0.2•C was observed for intensive roof gardens. ...
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Today almost fifty five percent of the world's population lives in cities. It is estimated that by 2050, the population would grow by 2.5 billion with about sixty eight percent of the world's population would be living in cities. Along with this population projection, it has also been estimated that the phenomenon of climate change will increase abundantly in this century and will lead to climate related extreme events. To combat such events in urban areas, their causes and consequences should be understood; to mitigate them and minimize the negative impacts of urbanization. Modification of land surfaces and uses in urban areas has proved to have drastic impacts on local climates. The net effect of central business districts, commercial areas and dense housing that replace natural land covers in urban areas greatly alter the exchange of energy and moisture between the surface and atmosphere; thereby modifying surface microclimate variables such as temperature and humidity (Menglin Jin, 2005).This often leads to the phenomenon of Urban Heat Island Effect in cities, whereby urbanized areas are characterized to have temperatures higher than those of their surrounding rural areas. Such elevations in temperature lead to substantial increase in thermal discomfort and air pollution, leading to deterioration of living environment and severe consequences on human health and well-being. It is estimated that about three billion people living in urban areas around the globe grieve to the problems caused by Urban Heat Island Effect (RIZWAN Ahmed Memon, 2007). Although Urban Heat Island Effect is not a direct consequence of global climate change and varies regionally at microclimate levels; it contributes to increased energy demands, straining air conditioning systems and contributing to global warming. The phenomenon is also expected to exacerbate due to the rising temperatures predicted in the framework of climate change scenario for the coming decades. To ensure a livable environment in cities, it is therefore of crucial importance to create sustainable built environments that are sensitive to this phenomenon. In this research, the Urban Heat Island Effect, its generation and impacts have been studied in detail using literature reviews. After a clear understanding of Urban Heat Island Effect has been established, design strategies for its mitigation have also been studied at Microscale levels from literature reviews. Along with their implementation, the potential reduction in temperatures resulting from these strategies have been analyzed. Post this study, a site has been chosen and a hypothetical-built environment has been created on the site where the design strategies have been tested through simulations. Envi Met software has been used for the simulations and the basic weather data for the site has been taken from secondary sources. The output from the simulations has been compared to the data obtained in the literature reviews to formulate 58 appropriate inferences. As the output from the simulations was based on basic weather data of the region, it has only been used for a comparative analysis and was not accounted to be 100% accurate. Additionally, while the Urban Heat Island Effect is a vast phenomenon in urban areas, the design strategies for its mitigation in this research have been limited only to buildings and their immediate outdoor environment.
... In order to adapt to climate change, including floods, a study was conducted that quantified technologies referred to as green infrastructure, such as roof gardens, permeable pavements, and ecological waterways [9,10]. Using a run-off analysis program such as SWMM (Storm Water Management Model), it has been revealed that green infrastructure such as roof gardens can not only reduce peak flow and flooding but also have a positive effect on carbon reduction and temperature reduction. ...
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... • C due to the application of green roofs [53] and the reduction was higher by 1.90 • C if the green roof was combined with trees and green walls. Another study by Kim showed that the temperature reduction was only by 0.3 • C with the installation of an intensive green roof [87]. Tsoka et al. [66] concluded that the maximum air temperature reduction in a green roof was between 0.1 • C and 1.7 • C, with the median value of reduction being close to 0.3 • C. ...
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This study quantitatively analyzed the effect of fog cooling on temperature reduction and conducted an optimization study on the layout for planning a fog cooling system in the Daegu Metropolitan City. First, the design and verification of a single fog cooling unit was identified through an indoor experiment. Second, the temperature reduction effect of the installed fog cooling system was measured based on a sensor and verified through a finite volume method (FVM)-based computational fluid dynamics (CFD) analysis. Third, a numerical analysis of the optimal fog cooling arrangement was designed and performed in the Indongchon area. The temperature reduction design manual and model equations, which can be used by decision-makers, were analyzed through numerical analysis. The measured temperature reduction and simulation values had a high accuracy of R² ≥ 0.8. Based on the verified model, scenarios A–D were designed and analyzed according to the fog cooling arrangement. Scenario B, in which the fog cooling was arranged vertically to the wind direction, appeared to be the most efficient. In this case, the volume average temperature where fog cooling was installed could be reduced by up to 3.02 °C. It was also found that efficiency is higher when the fog cooling system is positioned at narrow intervals of ≤5 m than at wide intervals of ≥10 m, considering the wind direction. The results of this study can aid decision makers—including urban policymakers and planners—for estimating the potential extent of temperature reduction and increase in humidity by adopting fog cooling.
This study is aimed to assess the performance of green roof-PV system; and determine the optimum installation height of green roof. In this study, two units PV panels of 1 kW each were setup at building rooftop level. Modular green roofs were established at three different heights of 0.3 m, 0.6 m and 0.9 m from rooftop floor level, respectively. The effects of each green roof height on the PV module temperature, ambient temperature and daily power yield were monitored for 6 months’ period. The results showed that green roof-PV system exhibited lower ambient and PV module temperatures of 3.36% and 17% compared to bare roof-PV system. Other than that, green roof enhanced the power generation efficiency averagely by 1.6%. It is found that green roof installed at 0.3 m has increased the power generation performance by 3% and 11% compared to that of 0.6 m and 0.9 m, respectively.
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In recent years, with the rapid increase in global warming and urbanization, urban heat island effects (UHI) have become an important environmental issue. Taiwan is no exception, with previous studies demonstrating serious UHIs in megacities. Although existing UHI research has utilized computer simulations to analyze improvement scenarios, there are few cooling strategy studies in actual blocks of Taiwan. Therefore, this study selected a block of a megacity in a tropical region of Taiwan as a case study by ENVI-met. Five improvement strategies were tested and compared to the current situation (B0): (1) Case C1 changed to permeable pavement, (2) Case C2 increased the green coverage ratio (GCR) of the street to 60%, (3) Case C3 changed to permeable pavement and increased the GCR in the street to 60%, (4) Case C4 changed to permeable pavement, increased the GCR in the street to 60%, and increased the GCR in the parks to 80%, and (5) Case C5 changed to permeable pavement, increased GCR in the street to 60% and parks to 80%, and set the GCR on the roof of public buildings to 100%. The results showed that the average temperature of the current thermal environment is 36.0 °C, with the comfort level described as very hot. Among the five improvement schemes, C5 had the greatest effect, cooling the area by an average of 2.00 °C. Further analysis of the relationship between the different GCRs of streets (SGCR) and the cooling effects revealed that for every 10% increase in the SGCR, the temperature of the pedestrian layer was reduced by 0.15 °C.
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The continuous worsening of urban thermal environments poses a severe threat to human health and is among the main problems associated with urban climate change and sustainable development. This issue is particularly severe in high-density built-up areas. Existing studies on the thermal environments (temperature data extracted from satellite remote sensing images) are mainly focused on urban canopy areas (airspace below the average height of trees or buildings) rather than the near surface region (at pedestrian height). However, the main outdoor activity space of urban residents is the area near surface region. Hence, this study aims to investigate the influence of urban form (i.e., building density, height, and openness) on thermal environment near the surface region. The high-density built-up areas of a typical megacity (i.e., Nanjing) in China were selected, and the thermal environments of 26 typical blocks were simulated using ENVI-met software. Temperature field measurements were carried out for simulation validation. On this basis, a classified and comparative study was conducted by selecting the key spatial form elements that affect thermal environments. The results showed that in actual high-density built-up areas, single urban form parameter does not determine the thermal environments near the urban surface but mainly affected by the use (function) of space. For this study, the overall thermal environment of a street block is optimal when the building density is between 40% and 50% and the average building height is between 8 and 17 stories. Nonetheless, the urban form can be improved to optimize the overall effects on building functions and thermal environments. Furthermore, function-specific urban form optimization strategies were proposed to optimize thermal environments according to specific functional needs.
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A job satisfaction survey was posted on the Internet and administered to office workers in Texas and the Midwest. The survey included questions regarding job satisfaction, physical work environments, the presence or absence of live interior plants and windows, environmental preferences of the office workers, and demographic information. Approximately 450 completed responses were included in the final sample. Data were analyzed to compare levels of job satisfaction of employees who worked in office spaces with live interior plants or window views of exterior green spaces and employees who worked in office environments without live plants or windows. Statistically significant differences (P < 0.05) were found regarding perceptions of overall life quality, overall perceptions of job satisfaction, and in the job satisfaction subcategories of "nature of work," "supervision," and "coworkers" among employees who worked in office spaces with live interior plants or window views and those employees who worked in office environments without live plants or windows. Findings indicated that individuals who worked in offices with plants and windows reported that they felt better about their job and the work they performed. This study also provided evidence that those employees who worked in offices that had plants or windows reported higher overall quality-of-life scores. Multivariate analysis of variance comparisons indicated that there were no statistically significant differences among the categories of "age," "ethnicity," "salary," "education levels," and "position" among employees who worked in offices with or without plants or window views. However, there were gender differences in comparisons of males in that male participants in offices with plants rated job satisfaction statements higher when compared with males working in offices with no plants. No differences were found in comparisons of female respondents.
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It is important to secure green spaces to solve the urban heat island phenomenon, which is among problems resulted by high-density developments in metropolitan areas. However, it is hard to secure such green spaces in established urban areas so Green Rooftop development approaches have recently been highlighted and introduced as a solution to the situation. The present study conducts a simulation on residential areas in urbanized regions to quantitatively evaluate the effects of green rooftop developments through a comparison of changes in the air temperatures before and after relevant development projects. According to the evaluation results, when the green roof top development is conducted in the available areas, the temperature is reduced by 0.14 degree. The extension of green project to the entire building showed the reduction of the temperature by 0.29 degree. Based on these results, it can be concluded that the green rooftop development is a practically solution for reducing the air temperature of urbanized areas.
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The significant shifts in climate variables projected for the 21st century, coupled with the observed impacts of ongoing extreme weather and climate events, ensures that adaptation to climate change is set to remain a pressing issue for urban areas over the coming decades. This volume of Progress in Planning seeks to contribute to the widening debate about how the transformation of cities to respond to the changing climate is being understood, managed and achieved. We focus particularly on spatial planning, and building the capacity of this key mechanism for responding to the adaptation imperative in urban areas. The core focus is the outcomes of a collaborative research project, EcoCities, undertaken at the University of Manchester's School of Environment and Development. EcoCities drew upon inter-disciplinary research on climate science, environmental planning and urban design working within a socio-technical framework to investigate climate change hazards, vulnerabilities and adaptation responses in the conurbation of Greater Manchester, UK. Emerging transferable learning with potential relevance for adaptation planning in other cities and urban areas is drawn out to inform this rapidly emerging international agenda. Approaches to build adaptive capacity challenge traditional approaches to environmental and spatial planning, and the role of researchers in this process, raising questions over whether appropriate governance structures are in place to develop effective responses. The cross-cutting nature of the adaptation agenda exposes the silo based approaches that drive many organisations. The development of a collaborative, sociotechnical agenda is vital if we are to meet the climate change adaptation challenge in cities.
The integration of rooftop greenhouses (RTGs) in urban buildings is a practice that is becoming increasingly important in the world for their contribution to food security and sustainable development. However, the supply of tools and procedures to facilitate their implementation at the city scale is limited and laborious. This work aims to develop a specific and automated methodology for identifying the feasibility of implementation of rooftop greenhouses in non-residential urban areas, using airborne sensors. The use of Light Detection and Ranging (LIDAR) and Long Wave Infrared (LWIR) data and the Leica ALS50-II and TASI-600 sensors allow for the identification of some building roof parameters (area, slope, materials, and solar radiation) to determine the potential for constructing a RTG. This development represents an improvement in time and accuracy with respect to previous methodology, where all the relevant information must be acquired manually.
Recent urban sprawl has destroyed various kinds of green space in tile city. It has affected duality of people's life in the city, as well as urban ecosystem. Recent study shows the possibilities of roofs as green spaces in urban central site where the land costs are generally high. This research focuses on Jung-Gu district in Daegu Metropolitan city as a study area and calculates possible area of green roof using 2002 Autocad program based on aerial photographs and land registration maps. And the purpose of this research is to analyze environmental and economic effects of green roof. The environmental effects are as follows. It is expected that 91,106m^2 green spaces, 12.13 % of study site, will be added if green roof is performed in the study site. It is assumed that the expanded areas could reduce the highest temperature to 0.5-1.0^{\circ}C during the summer in terms of environmental effect. And the following shows the economic effects. If green roof and greening urban central site are created as a same size of 91,106m^2, it will be expected that the costs of green roof will be much more in-expensive than about 98 billions won. It will be also found that the expense of cooling energy can be saved out about 8 millions won per day in summer, if grass planting is accomplished on the possible areas of green roof in the study site. Therefore, it is desirable to take legal supports such as enacting regulations to activate green roof for more environmental and economic effects. For instance, green roof for public institutions, school and model area selection are desirable method to publicize the effect of greening program for citizen's participation.
Recently, concerns about conserving proper size of urban green spaces and accessibility are increasing, regarding it as a solution to diverse urban environmental problems including pollution, ecosystem deterioration, urban climate change. Artificial ground greening such as green roofs is regarded as the only alternative that can conserve green spaces which are impossible to be secured on the ground. However, green roofs are not popularized yet and levels are very low in provincial cities despite of related technology development and support systems of related agencies. Based on the background, this study tries to present a theoretical basis of methods for green roofs, conducting green roof simulations Finally, it aims to offer base data which help establish policy direction for activation of green roof technology. As a result of a simulation for verifying temperature reduction effect, it was possible to affirm effect of a plot that green roofs applied. Especially, it was revealed that a green roof method using ground covers such as mixed planting was the most effective way to reduce temperature. Based on precise analysis of the users, actual study for activation of green roofs should be developed in the future, by presenting a standard model for experiments and obtaining information about examples of green roofs on private houses.
The purpose of this study, the type of rooftop learn more about the psychological benefits to users has been carried out, and healthy college students were examined in 40 patients. Conduct research to make the rooftop of the type of lawn, trees, ecological garden, wetland biotope, flowering plant in Seoul were divided into six groups. Measurement methods based on the type designation of the Planting and landscape photography by once the participants for each 10 minutes to watch and mood state tests (POMS) and the mean fractionation (SD), based on survey information about the psychological effects were correlated. Mood States test lawn, tree-oriented type, flowering plant stability in type, kindness, openness, and the effect of raising warme there was a tension, anxiety, depression, anger inhibition was effective. In contrast, depression and fatigue are common rooftop greening, respectively. The results in terms of the psychological effects of the type of rooftop garden ecology and wetland biotope than lawn, tree-oriented type, flowering plant types of users with a positive psychological effect seemed to be better.