Examining the impact of urban canyons morphology on outdoor environmental conditions in city centres with a temperate climate

Abstract

• The relationship between urban geometry parameters and outdoor environmental conditions in urban areas was examined. • The study tested threshold values in urban design guidelines by experiential means. • The findings demonstrated the effect of urban geometry parameters as environmental mitigation measures. The concept of future-proofing cities seeks to minimize environmental impacts and achieve sustainability by utilising various mitigation and adaptation techniques, specifically by improving urban fabric. Different urban forms and parameters have been extensively investigated in hot, arid and humid climates, however, it is less in temperate climates. In the UK, the current local urban design guides meet the needs of designers and urban planners, however, these guides are still considered descriptive and lack in-depth environmental assessment. This study aims to investigate the recommended threshold values in the National Model Design Code against real sites with different urban canyons morphologies to examine their impact on outdoor environmental conditions. The study used quantitative methods by conducting a review study, a survey of UK urban design guides and modelling using simulation via RayMan and IESVE. The study targeted pre-selected sites in Cardiff and Bristol that were identified as zones with urban heat stress. The results showed that the Aspect Ratio and Sky View Factor in two cities have significantly impacted outdoor environmental conditions in urban areas subsequently affecting the Physiological Equivalent Temperature (PET). The results showed that the recommended values have a significant impact on the outdoor thermal performance of the pre-selected urban canyons. The findings demonstrated that modifying the width of streets and changing the Aspect Ratio and SVF resulted in achieving a positive impact during summer when both factors have a direct relationship. However, when the Aspect Ratio and SVF have an inverse relationship, the results showed extreme cold stress during winter. Therefore, maintaining a direct relationship between the Aspect Ratio and SVF would help to improve outdoor conditions.