Temporal changes in temperature-related mortality in relation to the establishment of the heat-health alert system in Victoria, Australia

Abstract

Extreme heat alerts are the most common form of weather forecasting services used in Australia, yet very limited studies have documented their effectiveness in improving health outcomes. This study aimed to examine the temporal changes in temperature-related mortality in relation to the activation of the heat-health alert and response system (HARS) in the State of Victoria, Australia. We examined the relationship between temperatures and mortality using quasi-Poisson regression and the distributed lag non-linear model (dlnm) and compared the temperature-mortality association between the two periods: period 1- prior-HARS (1992-2009) and period 2- post-HARS (2010-2019). Since the HARS heavily weights heatwave effects, we also compared the main effects of heatwave events between the two periods. The heatwaves were defined for three levels, including 3 consecutive days at 97th, 98th, and 99th percentiles. We also controlled the potential confounding effect of seasonality by including a natural cubic B-spline of the day of the year with equally spaced knots and 8 degrees of freedom per year. The exposure-response curve reveals the temperature mortality was reduced in period 2 in comparison with period 1. The relative risk ratios (RRR) of Period 2 over Period 1 were all less than one and gradually decreased from 0.86 (95% CI, 0.72-1.03) to 0.64 (95% CI, 0.33-1.22), and the differences in attributable risk percent increased from 13.2 to 25.3%. The reduction in the risk of heatwave-related deaths decreased by 3.4% (RR_p1 1.068, 95% CI, 1.024-1.112 versus RR_p2 1.034, 95% CI, 0.986-1.082) and 10% (RR_p1 1.16, 95% CI, 1.10-1.22 versus RR_p2 1.06, 95% CI, 1.002-1.119) for all groups of people. The study indicated a decrease in heat-related mortality following the operation of HARS in Victoria under extreme heat and high-intensity heatwaves conditions. Further studies could investigate the extent of changes in mortality among populations of differing socio-economic groups during the operation of the heat-health alert system.

Keywords: Australia; Extreme temperature; Heat-action plan; Mortality; Victoria.

Fig. 1

Weather forecast districts and corresponding heat health temperature thresholds. (Source: Extreme Heat Sub-plan for Victoria (2017))

Fig. 2

Distribution of the average temperature by period

Fig. 3

Overall cumulative temperature-mortality relationship for the two study periods (1992–2009 and 2010–2019). Shaded areas correspond to a 95% confidence interval

Fig. 4

The main effect of heatwaves on the risk of death for two periods. The blue circle and the red diamond present the relative risk for period 1 and period 2, respectively. The vertical line presents 95% CI.