Impact of green roof on urban canopy layer microclimates in planned residential area of Dhaka, Bangladesh

Abstract

Dhaka is a fast growing city in Asia. To accommodate the population of this city, Dhaka has been growing both horizontally and vertically. As a result, much needed green spaces are being replaced by built-up areas at an unprecedented pace and leading to Urban Heat Island (UHI) effect. As the UHI effect is caused mainly due to widespread use of synthetic materials like asphalt and concrete, it results in increased heat storage capacity and reduction of evapotranspiration. As a result, the outdoor temperature of densely built-up areas in Dhaka is higher than the immediate urban zones, and the average meteorological record. Urban Heat Island effect stresses both electricity supply and quality of urban life. A proven way to balance the thermal budget and quality of life in buildings or cities is by improving the building envelope as well as the cityscape. In this shortfall of urban land and continuous pressure of urbanization, green roofs can be a potential remedy to this problem. Previous studies have identified green-roofs’ benefits in cooling off and energy-conservation in urban multi-storied buildings. However, limited exploration had been done to its wider influence on urban canopy layer microclimate. This study is concerned with the microclimatic aspects within urban canopy layers, and the impact of the green roof on planned residential areas. This study is multidisciplinary in character. Overall, it is an experimental research, which includes a combination of experimental method and simulation method. Field investigation was conducted to find out the existing condition of microclimate at Urban Canopy Layer (UCL) for selected sites. To identify the impact of the green roof on UCL, simulation studies were done. The result of this study will help us understand the status of the present microclimate of planned residential areas in a tropical city, Dhaka. It will shed light on the thermal impact of the green roof on microclimate within the UCL. Additionally, this study will yield directions for developing possible strategies for using green-roof in tropical urban contexts based on findings relating to the possible influence of green roof on near ground environment. The findings would highlight the potentials of green-roof as a retrofitted solution or as a new installation for cooling, mitigation of urban heat island effect and for providing a more desirable outdoor environment for urban residents.