Assessing Microclimate and Outdoor Thermal Comfort in the Urban Environment: A Case Study of Auckland, New Zealand

Abstract

Urban microclimate and outdoor thermal comfort play a critical role in enhancing liveability, particularly in dense urban environments. The impacts of climate change, the urban heat island effect, and growing urban populations necessitate a deeper understanding of how urban design influences microclimates and thermal comfort. This research aims to investigate these dynamics at Auckland University of Technology (AUT), New Zealand, focusing on identifying thermal risk areas and proposing strategies to mitigate negative impacts through informed urban design.

The research addresses a significant gap in the literature on outdoor thermal comfort in temperate oceanic climates (Cfb), especially in the context of Auckland. Despite extensive studies in other climate zones, research on cities with similar climates remains underexplored. This thesis provides a comprehensive analysis, drawing on insights from New Zealand, and aims to contribute to the development of design guidelines to improve thermal comfort in urban settings.

A mixed-methods approach was employed, combining field measurements, site observations, and surveys, alongside computational fluid dynamics (CFD) simulations using Envi-met and ANSYS software. Field data were collected to assess meteorological conditions, while surveys captured pedestrian thermal perceptions. Simulations were used to model the microclimate and outdoor thermal comfort across various design scenarios.

The research follows six main phases: (1) assessing previous location selection criteria for analysing microclimate and outdoor thermal comfort, (2) reviewing existing studies on outdoor thermal comfort in Cfb cities, (3) analysing microclimatic research in New Zealand and Australia to identify gaps and provide recommendations, (4) identifying thermal risk areas at Auckland University of Technology (AUT) and proposing new design scenarios to reduce thermal discomfort, (5) assessing pedestrian wind speed levels at AUT by defining a modified wind comfort criterion for Auckland, and (6) analysing the impacts of historical and predicted future climate data on the outdoor thermal comfort of Auckland.

The key findings reveal that high-density areas with limited greenery exhibit elevated thermal discomfort, particularly during summer. Replacing concrete walls with green walls and planting trees significantly reduces thermal discomfort. Wind analysis demonstrates that street orientation, especially those angled at 45 and 90 degrees to prevailing winds, exacerbates wind discomfort, whereas parallel orientations reduce wind speed impact. Future climate scenarios predict an increase in outdoor thermal discomfort, with projected temperature rises of 5°C in summer and 4.5°C in winter by 2110 under RCP 8.5.

The research contributes original insights by proposing a modified wind comfort criterion for Auckland and demonstrating the critical role of greenery in mitigating thermal discomfort. It highlights the importance of street orientation and aspect ratios in wind-speed regulation. These findings offer valuable guidelines for urban designers, local authorities, and policymakers to enhance outdoor comfort in Auckland’s urban environment, aligning future developments with climate-resilient strategies.