The influence of urban design on microclimate and thermal comfort around buildings
Erik Johansson, Civil Engineer PhD Eng.
In many developing tropical countries, rapid urban growth leads to several problems, including increased thermal stress. This has negative consequences for people’s health and well-being, and affects social and commercial outdoor activities negatively. Consequently, the creation of thermally comfortable microclimates in urban environments is highly important.
The main aim of this thesis is to deepen our knowledge regarding the relationship between urban design, microclimate and outdoor thermal comfort through studies conducted in the hot dry climate of Fez, Morocco, and the hot humid climate of Colombo, Sri Lanka. Both cities have highly uncomfortable climates and are experiencing problems of rapid population growth, leading to considerable horizontal expansion of urban development, characterised by inefficient land-use.
The research methodology in this study included a combination of microclimate measurements, numerical microclimate simulations and studies of the urban planning process. Field measurements were conducted in areas with significantly differing characteristics, including variations in urban geometry and distance to the sea, to map variations in microclimate and outdoor thermal comfort within each city. To cover a wider range of urban design, to test the impact of different design parameters on outdoor thermal comfort and to achieve optimum design solutions, microclimate simulations using the ENVI-met software were conducted. The urban codes were analysed to determine whether they favour or hinder climate-conscious urban design, while the interviews with urban planners and designers aimed at investigating the extent to which climate aspects are included in urban design.
Microclimate conditions and thermal comfort at street level were found to vary considerably within both Fez and Colombo. Apart from its old city, Fez is a dispersed city dominated by street canyons with low height-to-width ratios. This study shows that new urban areas would need to be far more compact than today’s to improve the microclimatic conditions during the warm season. However, deep canyons should be blended with shallower, east-west oriented canyons, as well as shallow open spaces to allow solar access in the winter. In Colombo, the urban form is also dispersed and a more compact form with deeper canyons is needed to improve microclimatic conditions. However, spacing between buildings is necessary to allow air flow. Shallow, east-west oriented canyons are needed near the coastal strip to enable the westerly sea breeze to penetrate the city. In both cities, design details, such as colonnades and shading trees, are important to improve pedestrians’ thermal comfort.
The dispersed urban form in both Fez and Colombo is the result of regulations regarding building heights, street widths, plot coverage and setbacks. The current urban codes do not favour a comfortable microclimate in either of the cities and would need to be changed to allow deeper street canyons and to promote the horizontal shading of pedestrians. Such a change would lead to higher building and population densities, which is in line with the aims of the national authorities in both countries. The consideration of climate aspects is limited at all planning levels in both cities. There is a need to educate professionals in climate-conscious urban planning and to develop detailed urban design guidelines and easy-to-use design tools.
Arid zones, Built environment, Climate ,Climatic design, Colombo, Developing countries, Fez, Humid tropics, Land-use, Micro climates, Morocco, Planning regulations, Sri Lanka, Thermal comfort, Tropical areas, Urban climate, Urban design, Urban planning.