Abstract
In this study we characterized the relationship between temperature and mortality in central Arizona desert cities that have an extremely hot climate. Relationships between daily maximum apparent temperature (ATmax) and mortality for eight condition-specific causes and all-cause deaths were modeled for all residents and separately for males and females ages <65 and ≥65 during the months May–October for years 2000–2008. The most robust relationship was between ATmax on day of death and mortality from direct exposure to high environmental heat. For this condition-specific cause of death, the heat thresholds in all gender and age groups (ATmax = 90–97 °F; 32.2‒36.1 °C) were below local median seasonal temperatures in the study period (ATmax = 99.5 °F; 37.5 °C). Heat threshold was defined as ATmax at which the mortality ratio begins an exponential upward trend. Thresholds were identified in younger and older females for cardiac disease/stroke mortality (ATmax = 106 and 108 °F; 41.1 and 42.2 °C) with a one-day lag. Thresholds were also identified for mortality from respiratory diseases in older people (ATmax = 109 °F; 42.8 °C) and for all-cause mortality in females (ATmax = 107 °F; 41.7 °C) and males <65 years (ATmax = 102 °F; 38.9 °C). Heat-related mortality in a region that has already made some adaptations to predictable periods of extremely high temperatures suggests that more extensive and targeted heat-adaptation plans for climate change are needed in cities worldwide.
Highlights
Deaths from exposure to extreme heat have been studied in cities on all inhabited continents [1,2,3,4,5,6,7].Motivating this research are high numbers of deaths during extreme heat events and projected increases in deaths from heat-related causes due to climate change [8,9]
The strongest relationship between mortality and temperature was for direct exposure to high environmental heat on day of death (Table 2, row 1 and Figure 2a)
We observed the lowest temperature threshold (ATmax = 93 °F, lag days = 0) and largest increase in the relative risk of death from heat exposure (RR = 1.20); i.e., daily mortality increased by 20% per 1 °F above threshold
Summary
Deaths from exposure to extreme heat have been studied in cities on all inhabited continents [1,2,3,4,5,6,7].Motivating this research are high numbers of deaths during extreme heat events and projected increases in deaths from heat-related causes due to climate change [8,9]. Heat waves in all types of climate zones cause many deaths in cities during short-term atypical weather. In cities with tropical and subtropical climates, hot weather lasts for long stretches during a prolonged warm season each year, leading to chronic heat exposure in the population [10,11]. Information about heat-related deaths in hot cities is important to hundreds of millions of people who live in them and contributes to understanding the limits of human tolerance to climatic conditions that may become more prevalent worldwide in this century. Average air temperatures in most cities are becoming warmer over time for two different reasons: global climate change and the urban heat island effect [12,13]. Current temperature-mortality relationships in hot cities are one indicator of the extent to which humans have adapted physiologically, behaviorally, and technologically to climate and offer insights about living in a future warmer world
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