A Global Assessment of Heat Stress-related Mortality

Extreme high temperatures are associated with elevated human mortality risks. This is evidenced by a typically U- or J-shaped relationship between daily temperature and mortality found for most places in the world where data exist. However, high temperature is not the only contributor to heat stress. Humidity is also an important factor because it affects evaporation of sweat, which is crucial for cooling the human body in hot environments. Although various heat stress metrics, many of which are a combination of atmospheric temperature and humidity based on different physiological assumptions, have been developed to estimate heat stress, the relationship between these metrics and mortality remains unclear. In this study, the relationships between four heat stress metrics ¾ wet bulb temperature, apparent temperature, discomfort index and swamp cooler efficiencies [1] ¾ and mortality are systematically assessed using well-established Distributed Lag Non-linear Models (DLNMs) [2]. The predictive powers of these metrics, as well as those of daily minimum, mean and maximum temperatures, are compared for the summer season at all global locations (spanning 43 countries) where sufficient meteorological and health data are available [3]. The results of this study provide new information as to which of these heat stress metrics are most indicative of summer mortality in different locations and climate zones. These results have important implications for developing national and international heat-health action plans, as well as for projecting future heat-related mortality under different climate change scenarios. References: [1] Buzan, J. R. et al.: Implementation and comparison of a suite of heat stress metrics within the Community Land Model version 4.5. Geosci. Model Dev., 8, 151170, 2015. [2] Gasparrini and Armstrong: Reducing and meta-analysing estimates from distributed lag non-linear models. BMC Medical Research Methodology, 13:1, 2013. [3] Vicedo-Cabrera, A. M. et al.: The burden of heat-related mortality attributable to recent human-induced climate change. Nature Climate Change, 11, 492500, 2021.