Spatial patterns of recent US summertime heat trends: Implications for heat sensitivity and health adaptations

Abstract

Heat is known to cause illness and death not only at extreme temperatures, but also at moderate levels. Although substantial research has shown how summertime temperature distributions have changed over recent decades in the United States, less is known about how the heat index-a potentially more healthapplicable metric of heat-has similarly evolved over this period. Moreover, the extent to which these distributional changes have overlapped with indicators of social vulnerability has not been established, despite the applicability of co-varying climatic and sociodemographic characteristics to heat-related health adaptations. Presented here is an analysis of trends in the median, 95th percentile, and 'warm-tail spread' (i.e., intra-seasonal range between the upper extreme and median) of warm-season (May-September) maximum heat index between 1979 and 2018 across the conterminous US. Using 40 years of data from the North American Regional Reanalysis dataset, it is shown that most of the US has experienced statistically significant positive trends in summertime heat, and that both the magnitude of trends and the shape of the frequency distributions of these measures vary regionally. Comparisons with data from the Social Vulnerability Index show that the most socially vulnerable counties appear to be warming faster than the least vulnerable, but that opposite patterns hold for trends in warm-tail spread. These findings may be applicable to further studies on climate change, heat adaptations, and environmental justice in the US. OPEN ACCESS RECEIVED

Anthropogenic Warming and Population Growth May Double US Heat Stress by the Late 21st Century

“…The decadal trends in WTS refers to the trends in intra-seasonal (here, summer (JJA)) range between the maximum and median of the daily HI during each of the 40 years climate scenario-time period combinations. Recent observed WTS trends are greatest in areas of the US with large socioeconomic vulnerability, underscoring the importance of comprehensively understanding future changes (Spangler & Wellenius, 2020).…”

“…Furthermore, daily fluctuations in HS severity, for values in the extreme and impactful range, often impose a considerable health burden with implications on heat‐related mortality (Ahmadalipour et al., 2019; Im et al., 2017; Matthews et al., 2017; Raymond et al., 2020). Even heat at moderate levels accompanied by large within‐season variability is known to cause illness and death, and more broadly is challenging for heat acclimation and long‐term adaptability (Spangler & Wellenius, 2020; Zanobetti et al., 2012). Recent increases in HS have coincided with the locations of greatest socio‐economic vulnerability across many parts of the US (Spangler & Wellenius, 2020).…”

“…Even heat at moderate levels accompanied by large within‐season variability is known to cause illness and death, and more broadly is challenging for heat acclimation and long‐term adaptability (Spangler & Wellenius, 2020; Zanobetti et al., 2012). Recent increases in HS have coincided with the locations of greatest socio‐economic vulnerability across many parts of the US (Spangler & Wellenius, 2020). To gain a fuller sense of how HS impacts may change, we use measures of HS extremeness and temporal variability to represent severity as well as possible acclimation (Matthews et al., 2017; Spangler & Wellenius, 2020).…”

“…Recent increases in HS have coincided with the locations of greatest socio‐economic vulnerability across many parts of the US (Spangler & Wellenius, 2020). To gain a fuller sense of how HS impacts may change, we use measures of HS extremeness and temporal variability to represent severity as well as possible acclimation (Matthews et al., 2017; Spangler & Wellenius, 2020).…”

Spatial and intraseasonal variation in changing susceptibility to extreme heat in the United States

“…This is particularly important because recent trends in summertime warming in the United States may be disproportionately greater in places with more SV. 18 …”