Changes in Susceptibility to Heat During the Summer: A Multicountry Analysis

Abstract

Few studies have examined the variation in mortality risk associated with heat during the summer. Here, we apply flexible statistical models to investigate the issue by using a large multicountry data set. We collected daily time-series data of temperature and mortality from 305 locations in 9 countries, in the period 1985–2012. We first estimated the heat-mortality relationship in each location with time-varying distributed lag non-linear models, using a bivariate spline to model the exposure-lag-response over lag 0–10. Estimates were then pooled by country through multivariate meta-analysis. Results provide strong evidence of a reduction in risk over the season. Relative risks for the 99th percentile versus the minimum mortality temperature were in the range of 1.15–2.03 in early summer. In late summer, the excess was substantially reduced or abated, with relative risks in the range of 0.97–1.41 and indications of wider comfort ranges and higher minimum mortality temperatures. The attenuation is mainly due to shorter lag periods in late summer. In conclusion, this multicountry analysis suggests a reduction of heat-related mortality risk over the summer, which can be attributed to several factors, such as true acclimatization, adaptive behaviors, or harvesting effects. These findings may have implications on public health policies and climate change health impact projections.

Community climate simulations to assess avoided impacts in 1.5 and 2 °C futures

“…Human impacts such as mortality vary disproportionately with the upper tail of the distribution of temperature (e.g., Guo et al, 2014;Gasparrini et al, 2016); hence, it is of relevance to consider the frequency with which historical temperature extremes will be exceeded in the future. We consider this in a couple of ways, firstly by adapting the methodology of Lehner et al (2016), which assesses the frequency with which records are exceeded in the future.…”

Climate change may alter human physical activity patterns

“…Fourth, our data are restricted to observations from one country with a temperate climate. It is critical to repeat this analysis where possible in countries with warmer average climates 49 and lower prevalence of air conditioning 50 , as they may see net reductions in physical activity due to climate change. Fifth, in this analysis we focus on recreational physical activities.…”

It’s not the heat, it’s the vulnerability: attribution of the 2016 spike in heat-associated deaths in Maricopa County, Arizona

“…There is some evidence that the timing of heat within the warm season may also be important to consider in modeling heat-related mortality (e.g. Gasparrini et al 2016). In Maricopa County in 2016 the six days with the highest mean temperature were split evenly between the months of June and July, which is consistent with the long-term climatology associated with the regional monsoon pattern that suppresses temperatures in late summer.…”

“…If population health risks related to heat are reasonably well approximated by widely applied time series models of the temperature-mortality association (e.g. Barnett et al 2012, Harlan et al 2014, Gasparrini et al 2016, our results indicate that factors other than the weather were predominantly responsible for the surge in heatassociated deaths in 2016.…”