International Journal of Biometeorology

, Volume 60, Issue 1, pp 85–98 | Cite as

Increased mortality associated with extreme-heat exposure in King County, Washington, 1980–2010

  • Tania Busch IsaksenEmail author
  • Richard A. Fenske
  • Elizabeth K. Hom
  • You Ren
  • Hilary Lyons
  • Michael G. Yost
Original Paper


Extreme heat has been associated with increased mortality, particularly in temperate climates. Few epidemiologic studies have considered the Pacific Northwest region in their analyses. This study quantified the historical (May to September, 1980–2010) heat-mortality relationship in the most populous Pacific Northwest County, King County, Washington. A relative risk (RR) analysis was used to explore the relationship between heat and all-cause mortality on 99th percentile heat days, while a time series analysis, using a piece-wise linear model fit, was used to estimate the effect of heat intensity on mortality, adjusted for temporal trends. For all ages, all causes, we found a 10 % (1.10 (95 % confidence interval (CI), 1.06, 1.14)) increase in the risk of death on a heat day versus non-heat day. When considering the intensity effect of heat on all-cause mortality, we found a 1.69 % (95 % CI, 0.69, 2.70) increase in the risk of death per unit of humidex above 36.0 °C. Mortality stratified by cause and age produced statistically significant results using both types of analyses for: all-cause, non-traumatic, circulatory, cardiovascular, cerebrovascular, and diabetes causes of death. All-cause mortality was statistically significantly modified by the type of synoptic weather type. These results demonstrate that heat, expressed as humidex, is associated with increased mortality on heat days, and that risk increases with heat’s intensity. While age was the only individual-level characteristic found to modify mortality risks, statistically significant increases in diabetes-related mortality for the 45–64 age group suggests that underlying health status may contribute to these risks.


Climate change Extreme heat Mortality Washington State 



Thank you to Matt Stumbaugh, Eric Salathé, and Alan Hamlet, with the University of Washington’s Climate Impacts Group, for providing the meteorological dataset as well as technical support. This work was supported, in part, by funding from the University of Washington’s Department of Environmental and Occupational Health Sciences Initiative Grant, the Centers for Disease Control and Prevention Cooperative Agreement, “Confronting the Health Risks of Climate Change” (1 U01 EH 000400-01), and the University of Washington Biostatistics, Epidemiologic and Bioinformatic Training in Environmental Health (BEBTEH) Training Grant - sponsored by the National Institute of Environmental Health Sciences (T32ES015459).

Ethical standards

This study complies with the Washington State Department of Health and University of Washington’s ethical standards. Data analyses were conducted after proper and appropriate human subjects approval was obtained from the Washington State Department of Social and Health Services IRB.


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Copyright information

© ISB 2015

Authors and Affiliations

  • Tania Busch Isaksen
    • 1
    Email author
  • Richard A. Fenske
    • 1
  • Elizabeth K. Hom
    • 1
    • 2
  • You Ren
    • 3
  • Hilary Lyons
    • 3
  • Michael G. Yost
    • 1
  1. 1.Department of Environmental and Occupational Health SciencesUniversity of WashingtonSeattleUSA
  2. 2.Department of EpidemiologyUniversity of WashingtonSeattleUSA
  3. 3.Department of StatisticsUniversity of WashingtonSeattleUSA

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