14th International Conference on Sustainable Environment and Architecture 2013
E03 Abstract Reference Number
Physical condition of green infrastructure in improving the environmental
comfort of urban area
Ashfa, Khairul Huda, Irzaidi
ArchitectureDepartment, Syiah Kuala University
Jl. TgkSyechAbdurrauf No. 7, Darussalam, Banda Aceh 23111, Indonesia email: [email protected]
Abstract - Green infrastructure as one of the urban infrastructures is not only important in terms of its quantity but also its physical quality in influencing micro climate and the comfort of city environment. The micro climate identification of green infrastructure of a city was conducted to find out the influence of tree density, tree composition, temperature, and air humidity. There were twenty locations of green infrastructures in Banda Aceh, based on their characteristics, selected to be the samples for this study. The measurement of physical condition such as tree density and the composition of tree types was conducted to identify its influence on the environmental comfort through multiple linear regression. Tree density and air humidity had a negative effect while tree composition had a positive effect.
Keywords: urban area, green infrastructure, tree density, tree composition, air humidity.
I. INTRODUCTION
Sustainable use of space needs a solid infrastructure planning to support the economic, social, and environmental lives in a region. Currently, a broader infrastructure, called green infrastructure which influences the sustainability and development of a community is being developed. Green infrastructure includes parks, city forest, conservation areas, recreation facilities, green belt and the others related to the nature or environment which is also the kinds of green infrastructure.
Green infrastructure is a technical term applied to the land or environment of high value and functions as an open space, Green infrastructure planning shows that forest and other vegetative elements of a landscape with important functional valuewhich should be recognized and protected [1].
Most of the focus of research on thermal comfort indoors. However, there also a lot of relevant research on outer space, which requires consideration of additional factors, such as solar radiation, wind, different activities, sweat rate, among others [2]. Thermal comfort based on the combination of solar radiation, high temperature, and low wind speed is still far below the expected comfort, especially on a sunny day. The very uncomfortable condition is on the roads with low buildings and without shadow of trees, while the very comfortable condition is on the roads with higher buildings which outdo the existing shadow of trees or in the coastal areas where gentle sea breeze provides positive influence. The town/city planner and architect propose to build a more compact city with the addition of more shadows through green infrastructure that it can protect the pedestrian paths. The opening of part of coastal area can make the gentle sea breeze blowing to the city [3].
Setyowati in discussing the condition of urban micro climate in the city of Semarang, took into account the existing tree density and tree types, even though their influence on the micro climate condition was unknown.
Setyowati also discussed about micro climate based on ideal temperature and comfort index [4]. The high rate of urbanization characterized by increasing built land (residential and industrial complexes) has become one of the causes of the widespread of urban heat island which is the extensive increase of high-temperature area (above 30°C). The expansion of heat island will result in the increase of discomfort of human life that human beings need cooling device such as air conditioner and fan which bring the impact in the form of electrical energy waste and pollution, and green house effect. Thus, it is necessary to think of the ideal city planning considering the area of green spaces and the high rate of urbanization to create comfortable life [5].
Conservation and green space development are good solutions [6] in controlling city growth. Green space plays an important role in the complex city ecosystem and provides ecosystem service including environment, esthetics, recreation, and economic benefit [7]. Green space preservatiuon and development become the main strategy in minimizing conflict between environmental quality and urbanization [6; 8; 9; 10].
The physical quality of the city of Banda Aceh as one of the tropical cities in Indonesia with several existing green infrastructure needs to be identified in improving theenvironmental comfort and city micro climate. This preliminary study seeks to answer the influence of the density and composition of trees on thermal comfort around the public open green spaces.
II. STUDY AREA, DATA, AND METHODS This study was conducted in the administrative area of the City of Banda Aceh which is geographically located between 5°16’15” - 05°36’16” N and 95°16’15” - 95°22’35” E. The area of this city is 61.36 km2. The average altitude of this urban area is 0.80 meters above sea level.
The population of this city was 228,562 persons (2011). The City of Banda Aceh comprises 9 subdistricts, 70 rural villages, and 20 urban villages. This study employed direct observation tecnique. Twenty locations for obeservation points were selected to be the samples for this study through purposive sampling technique, which are generally as city parks.
The research variables were optimum temperature, air humidity, tree density, and composition of tree types. All the three variables chosen in are listed in Table 1. Temperature and air humidity measurement on each research location were observed for two days (Monday and Sunday) [4]. The time for collecting data from each samples was based on the highest temperature in several years according to the Central Bureau of Statistics (BPS) and for this study it was decided to be on June 19 and 20, 2011. The equipment used in this study was the image of the city of Banda Aceh, GPS, thermometer, and hygrometer.
Figure 1. Study Area To analyze the condition of micro climate, the
parameters observed included as [4], 1) morning temperature (Tp), daytime/mid-day temperature (Ts), and afternoon temperature (Tsr) obtained based on the result of on-site measurement using temperature thermometer put at every location of observation points, 2) optimum temperature (Ti) was determined from the result of morning and daytime temperature measurement by using Thom formula [4], Ti = 0.2 (Tp + Ts) + 15 or Ti = 0.2 (Tmax + Tmin) + 15, where Tmax = maximum temperature (°C) and Tmin = minimum temperature (°C).
Biodiversity is a term showing the existence of various kinds of shapes, appearance, number and nature of the degree of natural diversity including
the number and frequency of the ecosystems and species or genes available in a certain area [11]. In addition, biodiversity is the number of kinds that can be reviewed using the three levels of natural diversities including the number and frequency of ecosystem, species or genes in a group. The levels of biodiversities are genetical diversity, species diversity, and ecosystem diversity [12]. Richard used the term of type composition to show the types of trees existing in the forest [13].
The formula used to count the composition of tree types [4] comprises C = composition of tree types, n = number of the types of shade trees per unit area, and N = number of shade trees per unit area. According [4], tree density (D) is determined by counting the number of shade trees per unit area
at respective research location. The formula used was the number of trees/location area (D). The tree meant in this study is all shade trees with minimum
trunk diameter of 10 cm, and using a 5 x 5 meter plot at the sample locations.
Tabel 1
List of variables included in multiple linier regression
Variabel Broad definition Unit Nature of variable
Dependent
Y Optimum temperature (Ti) celcius degree Continuous
Independent
X1 Tree density index (DI) percentage Continuous
X2 Tree composition index (CI) percentage Continuous
X3 Air humidity (AH) percentage Continuous
The next stage was to make an estimation model of optimum temperature as the dependent variable, with tree density, composition of tree types, and air humidity as the independent variables by using multiple linear regression and the following formula of estimation in general:
Ti = b0 + b1X1 + b2X2 + b3X3 + ε ……...…. 1)
III. RESULT AND DISCUSSION The result of analysis showed that green infrastructure in the City of Banda Aceh in general had a rather hot and dry temperature as seen in Figure 2 and Figure 3. The climograph on June 20, 2011 showed that many locations had high humidity (60 to 80) in the morning and in the afternoon. During the day, most of the humidity was between 40 to 60 as seen in Figure 4 and Figure 5.
The observation point with the highest value of tree density is Taman Hutan Kota (THK). The lowest tree density index is found in Simpang Tujh Ulee Kareng (STU). Parks generally have higher density values than non-park, like as Taman Sari (TMS), Taman Putroe Phang (TPP), Taman Adipura (TPA), Taman BTPN (TBT), and Taman Tibang (TTB), which generally around 20%.
(Figure 6). For tree composition, In general, each park has a value of CI is to be around 20% to 30%.
The result of observation done on the air humidity in the city parks and other green infrastructures such as city park and city forest.
City forest provides more optimal shade due to its optimal tree density. Based on the result of air temperature measurement, the temperature in the city forest was not much different from that in the city parks with low tree density.
During the day, the highest temperature is found in the area of Ulee Kareng (37.2°C) while the lowest temperature is in Taman Putroe Phang (33°C) with their respective air humidity of 57.70 and 63.10. This occurs due to the still minimum reforestation at Ulee Kareng area. There is not any public green infrastructure yet in this area and in
the vicinity of this area, there are shop buildings without having greenery around it. The figures showed that the higher the air humidity, the lower the air temperature will be.
The ideal temperature for both locations is respectively 28.66°C and 27.80°C. With the category of air temperature, the air temperature around the locations belongs to rather hot category or still under 29°C. Of all the sample locations, only Taman Adipura belongs to hot category. It occured due to the less reforestation and the heat resulted from the roads around the park. The ideal temperature for Taman Adipura is 29.02°C with air humidity of 54.4. With such humidity, each of the locations mentioned above belongs to dry category.
The index of comfort is found by connecting ideal temperature with the existing humidity. In relation to the environmental comfort in the existing green infrastructure, it can be obviously explained that the discomfort in the locations where samples were taken occured more frequently on June 19, 2011 where 8 (eight) locations such as Simpang Tujuh Ulee Kareng, Taman Adipura, and Lapangan Tugu Darussalam (LTD), had the index of comfort above 26.00.The other parks such as Taman Sari, Taman Potroe Phang, Taman BTPN and Taman Hutan Kota, across from Mesjid Raya (the Grand Mosque) belonged to comfortable category. On June 20, 2011, based on the index of comfort, 2 (two) locations such as Taman Adipura and Simpang Tujuh Ulee Kareng, belonged to uncomfortable category.
Figure 4 and Figure 5 shows the relationship between temperature (°C) and air temperature (relative temperature) in the 20 sample taking areas. Both figures showed the spread of temperature and air humidity in the morning, mid- day, and afternoon condition. A conclusion can be drawn from both figures that the climate condition in the morning was not too much different from that in the afternoon, but, in the daytime, almost all of the locations showed high temperature and low air humidity. The climate condition in the daytime was much different from that in the morning and in the afternoon.
Figure 2 Temperature Condition of Green Infrastructure on June 19, 2011
Figure 3 Temperature Condition of Green Infrastructure on June 20, 2011
The condition on June 19, 2011 was a bit different compared to that on June 20, 2011. It could be seen on June 19, 2011 that several places experienced high air humidity, especially in the morning. It was assumed that the urban community did less activities on that day (holiday) that the use of motor vehicles was reduced . So happened during the day, in the daytime and in the afternoon, several sample taking locations had the air humidity between 60 and 80.
The other explanations were related to the treen density and the composition of tree types in
the parks. Figure 6 also shows that all of the green infrastructure of city park had a very small (very sparse) density index. So was the composition of the types of the shade trees planted in those parks.
This happened because most of the trees planted in the parks are ornamental plants not shade trees.
By using statistic analysis, the estimation model to find out the optimum temperature around the infrastructure in Banda Aceh can be found as follows:
Ti = 29,761–0,098DI+0,143CI–0,025AH (3)
Figure 4. Climograph on June 19, 2011 Estimation model as shown in the Equation 3
above explains that tree density and humidity also contributed in explaining variable of temperature, where the variables had negative influence on air temperature which means that the denser the trees and humidity in a park, the lower the air temperature will be. Each time the density
increases for 1%, the air temperature will decrease for 0.098°C. Each time the humidity increases for 10%, the air temperature will decrease for 0.025°C.
The kinds of trees planted had a positive influence meaning that the higher the value of the variable, the increasingly higher the air temperature will be.
Figure 5. Climograph on June 20, 2011
IV. CONCLUSION
The micro climate condition of green infrastructure is identified through the condition of temperature, air humidity and index of comfort. In general, the temperature in the vicinity of green infrastructure
in the City of Banda Aceh is rather hot and the air humidity around the green infrastructure is dry. The consequence is that the less comfortable condition occurs in the vicinity of green infrastructure. Tree density, tree composition and air humidity in the green infrastructure has influence on the
temperature. Tree density and humidity have negative influence while tree composition has positive influence. Further study should be conducted using spatial analysis and considering the aspect of the form of green infrastructure, in related with the composition of trees. Beside it, more accurate estimates will be required which can
be done by an expansion model with more variables and samples, which can help us to learn more about the advantage of the composition and density of trees in improving climatic condition.
Reference [14] explains that unfovarable climatic conditions can be improved by planting trees in the city structure.
Figure 6. Density index and tree composition in the city parks
ACKNOWLEDGMENT
We would like to express our gratitude to Syiah Kuala University to support this study and to Dr.
Abdullah for giving us his many valuable insights and suggestions. I would also thank Azzyati Himida for her assistance and participation in collecting the data for this study.
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