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Article Excerpt
Abstract: It is widely known that greenery has positive impacts to the environment. It is necessary to consider greenery as an important element in any contemporary urban planning. However, planners, estate managers and property managers are not able to asses existing greenery conditions in terms of quantitative data in order to achieve their goals in maintaining or improving the greenery condition. Thus, it is impossible to set a framework or plan to improve the environmental quality. The objective of this research is to develop a framework for planners to evaluate and to improve the greenery conditions in planning the urban environment.
Keywords: GIS, Greenery condition assessment, Greenery mapping framework, Planning, Urban environments
Introduction
At the macro-scale, the main influencing factor in determining the climate on earth in solar radiation (Henderson-Sellers, 1987; Kiehl, 1992). According to an earth energy budget by Schneider (1992), 45% of incoming solar radiation is absorbed by the surface of the planet, 25% by the atmosphere, and 23% is reflected by the atmosphere. In a built environment at the micro-scale level, the surrounding conditions, especially buildings and vegetation, influence the incident solar radiation received by a surface. This is determined by the "openness" of a surface, which is called the sky view factor (Cleugh, 1995). Therefore, these three urban elements, which include buildings, greenery and paved areas and streets, play an important role in governing the microclimatic condition.
Planting of vegetation is one of the methods to reduce the high ambient temperature in the environment and in any microenvironment in particular. One tree can generate coolness, but its impact is limited only to its surroundings (Jauregui, 1990/1991). A group of trees, for example, a park, extends the benefit of trees. A large park can reduce the ambient temperature in a built area with the average of 1.3[degrees]C as compared to having no park near a built-up area (Chen, 2006).
Researchers have also done studies observing the temperature between greenery areas and built environment areas based on satellite imagery (Kawashima, 1990/1991). In the urban area, the surface temperature ranged from 1.4 to 2.7[degrees]C on the green area, while it ranged from 2.0 to 3.4[degrees]C on buildings, and 2.3 to 4.9[degrees]C on the soil. In the countryside, the surface temperature ranged from 2.6 to 2.8[degrees]C on forests, while it ranged from 3.3 to 4.2[degrees]C on buildings and 5.1 to 5.9[degrees]C on the soil (Kawashima, 1990/1991).
Wong and Chen (2006) studied the impact of intensive and extensive rooftop greenery to the building and environment. Rooftop greenery is able to provide benefits not only to the building but also to the surrounding air temperature. With the intensive rooftop greenery system, the surface temperature may be reduced up to 31[degrees]C and the ambient temperature at 1 meter above the surface may be reduced up to 1.5[degrees]C. On a metal roof, the impact of rooftop greenery in terms of temperature reduction is even greater. Without plants, the metal surface can be up to 60-70[degrees]C during daytime and lower than 20[degrees]C at night. Meanwhile, if the metal roof is planted with plants, it ranges only from 24[degrees]C to 32[degrees]C.
Streiling (2003) investigated the influence of single and small cluster groups of trees on the bioclimatic of the city. The areas planted with trees can have a maximum temperature of 2.2[degrees]C higher than the areas without trees. The mean differences in air temperature were 1.0[degrees]C and 0.9[degrees]C respectively.
From some of the studies mentioned above, it is clear that the size or area of urban elements (building, greenery and pavement) determines the temperature of a built environment. The larger the size of the greenery area, the lower is the ambient temperature.
However, having a large greenery area in a small development area maybe a constraint. For example, Singapore is a small country where land is very limited for future development. However, on the other hand, the Singapore Government should not open the natural reserves area for new building development. One of the available solutions is the application of rooftop greenery.
Switzerland has just passed a bylaw that the architect or developer must design their new buildings to relocate the green space covered by the building's footprint to their roofs. This applies even for existing buildings including historical buildings where 20% of their rooftops must be green up (Johnson, 2002). The Singapore Government may consider the experience of Switzerland seriously. This should be the main goal in order to maintain a sustainable environment.
To achieve this goal, there is a problem faced by the planners or estate managers, especially for a large estate development. It is the lack of quantitative data on the greenery condition of their estates in order to maintain or improve the greenery condition. The quantitative data means all of the greenery parameters such as the area, the type and the density of the greenery. The greenery data, which the estate managers have, is usually the archive of the landscape designs and very often, they are out of date. It is because the greenery in an estate usually serves mainly for esthetical purpose rather than for environment consideration. Thus, for the planners or estate managers who want to shift their greenery objective, they do not have an assessment tool or framework to measure their goals.
The study presented in this paper is the extension of Singapore Urban Heat Island study (Wong, 2004) and part of the micro-scale Urban Heat Island study in the National University of Singapore (NUS), Kent Ridge Campus (Wong, 2008). From the field measurement on a...
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