Mapping Summer Microclimates Across the City of Sydney, Australia

The City of Sydney is a world-class tourism destination and economic powerhouse in the southern hemisphere. The city is exposed to the impacts of climate change, including increasingly hot summer air temperatures. Its proximity to the Pacific Ocean and its location in the Sydney Harbour provides generally more benign summer temperatures compared to those experienced further west in the Sydney Basin. Yet, air temperatures during extreme heat events are regularly above 40°C and present health risks for local populations. Making important, lasting and effective decisions where and how issues related to urban heat should be addressed requires a sound understanding of the thermal environment across the city. This report provides this knowledge. It is the most detailed, observed analysis of urban microclimates across the city to date. Near-surface air temperatures (3-4 metres from the ground) were recorded at 127 locations that included public parks, residential streets, the foreshore, sport fields and industrial hubs. Also, at some sites, relative humidity was recorded to better understand outdoor thermal comfort. More than 1.5 million measurements were collected between December 2023 and March 2024. Large datasets were used to rank suburbs according to their mean, maximum, minimum, daytime and nighttime air temperatures. Data analyses revealed clear north-south thermal gradients during hot (maximum air temperatures at or above 35°C) and extreme heat days (maximum air temperatures at or above 40°C). While it was 30°C at the Royal Botanic Gardens (north), communities in Alexandria or Roseberry (south) endured temperatures above 40°C at the same time. The hottest day during summer was 9 December 2023 when air temperatures at Church Street in St Peters (southern section of the city) soared to 45.3°C, clearly presenting high thermal stress and related health risks. In a world-first, microclimate animations revealed the intensity and spatial extent of the Harbour Breeze when cooling the city. The present work provides the starting point for evidence-based heat mitigation. Understanding the microclimatic variation among landscapes dominated by grey, blue, green and transport infrastructure will assist city managers in developing effective strategies that increase resilience of the city against heat. Several broader recommendations to increase the capacity of the City of Sydney to mitigate and adapts to increasing summer heat are provided at the end of the report. These include top-down actions related to policy development, bottom-up actions that can improve heat resilience at the household level and strengthen community preparedness in the wake of extreme heat events. Results from this study will help the City of Sydney to continue and broaden its leadership in establishing a heat-resilient city.