Influence of Heatwave Intensity, Duration, and Timing in Season on Heatwave Mortality Effects in the United States

Abstract

O-30A3-2 Background/Aims: Devastating health effects from recent heatwaves, and projected increase in frequency, duration, and severity of heatwaves from climate change, highlight the importance of understanding health consequences of heatwaves. We analyzed how mortality risk for heatwaves in 43 US cities (1987–2005) relate to heatwaves. Methods: Heatwaves were defined as >2 days with temperature >95th percentile for the community for 1 May–30 September. Heatwaves were characterized by their intensity, duration, and timing in summer. Within each community, we estimated mortality risk during each heatwave compared to non-heatwave days, controlling for potential confounders. We estimated how heatwave mortality effects were modified by heatwave characteristics (intensity, duration, timing in summer). Results: Nationally, on average, heatwave mortality risk increased 2.49% for every 1°F (0.56°C) increase in heatwave intensity and 0.38% for every 1-day increase in heatwave duration. Heatwaves were associated with a 5.04% (95% confidence interval: 3.06%–7.06%) increase in mortality risk compared to non-heatwave days for the first heatwave of the summer versus 2.65% (95% confidence interval: 1.14%–4.18%) for later heatwaves. Heatwave mortality impacts and effect modification by heatwave characteristics were more pronounced in the Northeast and Midwest compared to the South. Conclusion: We found higher mortality risk from more intense, longer, or earlier heatwaves. Findings have implications for decision-makers and researchers estimating health effects from climate change.