Mortality Associated with Extreme Heat in Washington State: The historical and projected public health burden

Abstract

Extreme heat is one of the most important pathways illustrating the connection between climate and human health, including in temperate areas such as the Pacific Northwest. Moreover, climate change is expected to exacerbate this important public health issue. This research has two components. First, a time-stratified case-crossover analysis is used to characterize the historical (1980 – 2018) association between summertime (May - September) heat and non-traumatic mortality in Washington state. A separate analysis is conducted for each of the state’s climate divisions to produce ten distinct exposure-response curves expressing odds of mortality as a function of humidex. Stratified analyses are used to assess the impact of age, sex, race/ethnicity, and select causes of death, and the reported results are pooled across all climate divisions using fixed-effects meta-analysis. Second, the historical heat-mortality relationship is combined with climate change projections to estimate the impact of a changing climate on heat-related deaths in 2030, 2050, and 2080 under two warming scenarios. The odds ratio and 95% confidence intervals of mortality at the 99th percentile of humidex compared to the 50th percentile did not include the null value in four of the ten climate divisions, and the point estimates in all ten divisions indicated increased risk of mortality at high values of humidex. Across Washington, the odds of mortality are 8% higher (6%, 10%) on 99th percentile days compared to 50th percentile days. Risk is higher for women than men and for Blacks than Whites. Risk also increases with age and for diabetic, circulatory, cardiovascular, ischemic, cerebrovascular, and respiratory deaths. 95% confidence intervals of projected heat-attributable mortality did not overlap with zero in three of the ten climate divisions. In these three divisions, the average percent increase in heat-attributable deaths across both warming scenarios is 35%, 135%, and 603% in 2030, 2050, and 2080, respectively, over the historical period. This research is the most extensive study of heat-related mortality in Washington to date and can help inform public health initiatives which aim to improve both present and future health outcomes in the state.