Drought severity and all-cause mortality rates among adults in the United States: 1968–2014

Abstract

Background Little is known about the effect of drought on all-cause mortality, especially in higher income countries such as the United States. As the frequency and severity of droughts are likely to increase, understanding the connections between drought and mortality becomes increasingly important. Methods Our exposure variable was an annual cumulative drought severity score based on the 1-month, county-level Standardized Precipitation Evapotranspiration Index. The outcome variables of demographic subgroup-specific all-cause mortality count data per year were obtained from the National Vital Statistics System. Any counts below 10 deaths were censored in that demographic group per county. We modeled county-stratum-year mortality using interval-censored negative binomial regression with county-level random intercepts, for each combined age-race-sex stratum either with or without further stratification by climate regions. Fixed effects meta-regression was used to test the associations between age, race, sex, and region with the drought-mortality regression coefficients. Predictive margins were then calculated from the meta-regression model to estimate larger subgroup (e.g., ‘race’ or ‘sex’) associations of drought with mortality. Results Most of the results were null for associations between drought severity and mortality, across joint strata of race, age, sex and region, but incidence rate ratios (IRRs) for 17 subgroups were significant after accounting for the multiple testing; ten were < 1 indicating a possible protective effect of drought on mortality for that particular subpopulation. The meta-regression indicated heterogeneity in the association of drought with mortality according to race, climate region, and age, but not by sex. Marginal means of the estimated log-incidence rate ratios differed significantly from zero for age groups 25–34, 35–44, 45–54 and 55–64; for the white race group; and for the South, West and Southwest regions, in the analysis that included wet county-years. The margin of the meta-regression model suggested a slightly negative, but not statistically significant, association of drought with same-year mortality in the overall population. Conclusions There were significant, heterogeneous-direction associations in subpopulation-stratified models, after controlling for multiple comparisons, suggesting that the impacts of drought on mortality may not be monolithic across the United States. Meta-regression identified systematic differences in the associations of drought severity with all-cause mortality according to climate region, race, and age. These findings suggest there may be important contextual differences in the effects of drought severity on mortality, motivating further work focused on local mechanisms. We speculate that some of the estimated negative associations of drought severity with same-year mortality could be consistent with either a protective effect of drought on total mortality in the same year, or with a delayed health effect of drought beyond the same year. Further research is needed to clarify associations of drought with more specific causes of death and with sublethal health outcomes, for specific subpopulations, and considering lagged effects occurring beyond the same year as the drought.

Effects of Drought on Mortality in Macro Urban Areas of Brazil Between 2000 and 2019

“…However, Lynch et al. (2020) revealed that drought did not affect males and females differently on all‐cause mortality among adults in the USA. Therefore, we firmly believe that further and conclusive studies are needed to clarify the association between drought exposure and mortality between both sex groups.…”

“…Drought exposure was measured by the Standardized Precipitation‐Evapotranspiration Index (SPEI; Vicente‐Serrano et al., 2010) which is widely used in drought analysis, including studies on health impacts as Lynch et al. (2020) and Salvador et al. (2019, 2020b, 2020c, 2021).…”

“…Therefore, the analysis of the implications of social conditions as modifier factors in the association between drought conditions and health outcomes is a pressing challenge because this phenomenon can affect health through different pathways and disproportionately affect specific groups of the society (Salvador et al., 2020a; Sorensen et al., 2018; UNDRR, 2021). Studies that integrate the gender perspective are essential due to the complexity in the association between gender and vulnerability to drought effects and the heterogeneity observed between regional studies (Lynch et al., 2020; Nellemann et al., 2011; Salvador et al., 2021; Wang et al., 2021; WHO, 2014).…”

Extreme Weather and Climate Change: Population Health and Health System Implications

“…Because of the difficulty in defining the beginning and end of a drought, the causal pathways connecting droughts to health outcomes can be complex and difficult to monitor (10,117). The most commonly identified pathway is a reduction in water availability for societal uses, both in quantity and quality as concentrations of pollutants increase (129).…”

Public Health Policy Actions to Address Health Issues Associated with Drought in a Changing Climate

“…Population subgroups are especially pertinent, as demographic characteristics can increase community susceptibility to drought related hazards. 27 Populations that are reliant on agriculture for livelihoods or sustenance are vulnerable to food insecurity, malnutrition, and the accompanying adverse mental health effects when drought causes economic loss. 28 Children and the elderly are both vulnerable to various drought-related health outcomes, such as air- and waterborne diseases.…”