Urban development and pedestrian thermal comfort in Melbourne

Abstract

In October 2013, “Plan Melbourne” was released by the Victorian government to outline the vision for Melbourne’s growth to the year 2050. The City of Melbourne’s draft municipal strategic statement identified “City North” as a great urban renewal area that can accommodate a significant part of the growth. Structure plans provide guidance to the community, planners, business, government and developers about the appropriate directions and opportunities for future changes in City North. Proposing street hierarchy, increasing the building heights, expanding the urban forest by increasing tree canopy coverage, implementing green roofs and overall transition from a low-rise to medium rise urban area are some of the strategies presented in structural plans. This study investigates the effect of future structural plans presented in “Plan Melbourne” on pedestrian thermal comfort in City North for extreme hot summer days. A three-dimensional microclimatic modelling tool ENVI-met 3.1 was used to evaluate the outdoor human thermal environment for the existing and future scenarios proposed by the Victorian government. Field measurements were carried out to validate ENVI-met and examine its ability in addressing the research objectives. Structural plans were modelled t in three stages; increased building height, adding tree canopy coverage and adding green roofs. The study showed that deeper canyons, higher aspect ratios and lower sky view factors in future scenario contribute to lower level of mean radiant temperatures (42°C–64°C), compared to the existing scenario (49°C–60°C). Physiological equivalent temperature (PET) was improved by 1°C–4°C as a result of “Increased building height” scenario. Increasing the tree canopy coverage caused 1°C–2°C reduction on PET level and adding a green roof did not show any improvement on PET at pedestrian level. Although the study showed a slight improvement in PET after implementing future structural plans, it was necessary to further improve PET level, particularly during certain hours of the day. Therefore long term planning strategies (integrating public realms with small urban parks and increasing the tree canopy coverage from 40% to 50%) were proposed and modelled to examine their effectiveness in further improving thermal comfort in an extremely hot summer day. Implementing future structural plans and proposed scenarios together resulted in 5.1°C improvement in the PET in an extremely hot summer day. The study also indicated that aspect ratio (H/W) is the most efficient strategy in decreasing Tmrt and PET during the day. Integrating climatic knowledge into planning practices in Melbourne metropolitan area would lead to less vulnerability to the extreme heat events and reduce the adverse impacts of increased air temperature on public health.