Mortality Burden of Heatwaves in Sydney, Australia Is Exacerbated by the Urban Heat Island and Climate Change: Can Tree Cover Help Mitigate the Health Impacts?

Abstract

Heatwaves are associated with increased mortality and are exacerbated by the urban heat island (UHI) effect. Thus, to inform climate change mitigation and adaptation, we quantified the mortality burden of historical heatwave days in Sydney, Australia, assessed the contribution of the UHI effect and used climate change projection data to estimate future health impacts. We also assessed the potential for tree cover to mitigate against the UHI effect. Mortality (2006–2018) records were linked with census population data, weather observations (1997–2016) and climate change projections to 2100. Heatwave-attributable excess deaths were calculated based on risk estimates from a published heatwave study of Sydney. High resolution satellite observations of UHI air temperature excesses and green cover were used to determine associated effects on heat-related mortality. These data show that >90% of heatwave days would not breach heatwave thresholds in Sydney if there were no UHI effect and that numbers of heatwave days could increase fourfold under the most extreme climate change scenario. We found that tree canopy reduces urban heat, and that widespread tree planting could offset the increases in heat-attributable deaths as climate warming progresses.

Incidence and risk factors of heat‐related illness in dogs from New South Wales, Australia (1997–2017)

“…High environmental temperatures are a known risk factor for dogs developing HRI. 46 The current results show that the highest rates of HRI occurred in 2004 and 2016, which corresponds to heatwave years 32 and see Figure 5 that shows the number of days with temperatures above the 95th percentile. Similarly, most HRI cases presented in months with elevated air temperatures, with most being reported in December/January which aligns with the Australian summer.…”

“…The monthly HRI incidence rates peaked in December and January during the Australian summer ( Figure 4). The highest incidence rate of HRI was reported in 2004 and 2016 (Figure 6), which corresponds with hotter years in Sydney 32 and see Figure 5).…”

“…The highest fatality rates were recorded in 2004 and 2016, during one of the hotter years in Sydney (Ref. 32 and see Figure 5).…”

Public health: a forgotten piece of the adaptation law puzzle

“…2 Extreme heat as a public health climate change impact Human metabolic temperature sits roughly around 35°C. Humans function most efficiently in environments below this temperature (Nairn and Fawcett, 2013) and problems arise for the human body when average temperatures rise over 35°C or remain above 30°C across a 24 h period (Chaston et al, 2022). Heatwaves are generally defined as abnormally hot weather that lasts for a period of 48 h or more (Nairn and Fawcett, 2013).…”

Urban gardening for mitigating heat island effect

“…They create an isolated heat island with its detached microclimate apart from nearby rural areas [2,3]. Some studies reported that mortality rates increased significantly in urban areas due to summer heat waves entangled with UHI [1,[4][5][6]. The fast-growing urban sprawl or urban expansion contributes to this increasing heat.…”