Cooling effect of urban river reserve vegetation structure in outdoor environment
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Date
2019
Authors
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Publisher
Universiti Teknologi Malaysia
Abstract
Urban river reserve or urban riparian is recognised as urban green space in Malaysia. According to the Department of Irrigation and Drainage (DID), this space is necessary for the stabilisation of riverbank, biodiversity, and water quality. However, there is no study conducted on the advanced functions of urban river reserve such as thermal reduction in a hot and humid climate. It is believed that vegetated urban river reserves can promote thermal reduction and improve microclimate conditions in urban areas. In Malaysia, the urban river reserve design is spatially constrained, which creates severe limitations for the thermal reduction strategy. The absence of a cohesive governmental guideline within different agencies further worsens the problem. This study has investigated the extensiveness of urban river reserve indicator as an urban green space and its associated thermal reduction properties. The cooling effect of urban river reserve and factors affecting the distribution of cooling effect were also determined. A total of 31 different zones of urban river reserves were formed to assess physical and vegetation compositions. Five representations were then selected for detailed field measurements. A surface-plant-air microclimate model and wind tunnel simulation were used to predict the impact of modification on measured parameters. The results showed that none of the surveyed urban river reserves was categorised as green infrastructure aquatic system typologies, and most of the areas were neglected spaces due to incivilities aspects. Most of the existing riverside urban green spaces were merely vegetative walls that divided the river and their adjacent area that cannot provide significant thermal reduction function. The urban green spaces which are vegetative wall experienced higher average diurnal temperature of 31.9°C compared to 30.6°C for urban river reserve which has been fully developed into a green park. The built-up areas adjacent to the urban river reserves with more than 80% of non-vegetated surface experienced higher average temperature with a difference of 2.7°C (±SD=1.6). The thermal reduction effect is substantial within the radius of 30m from the river edge. The results showed that the cooling effect differs based on green area coverage, type of vegetation coverage, vegetation formation, specific green volume and vertical clearance height. The minimum vertical clearance height of 2m between tree canopy and understory growth was necessary to ensure sufficient convection over evaporative surface for increased ventilation. Therefore, vegetation structure and detail specification are crucial in extending thermal cooling effect on areas straddling the river. This study is useful for future use of urban development policies and design. The application of these parameters could improve the living conditions for future river developments.
Description
Thesis (PhD. (Civil Engineering))
Keywords
River engineering—Environmental aspects, Urban ecological design, Urban hydrology, Riparian areas