Understanding drought's impacts on human health
Authors: John Balbus
Journal: The Lancet Planetary Health (2017)

The study by Jesse Berman and colleagues1Berman JD Ebisu K Peng RD Dominici F Bell ML Drought and the risk of hospital admissions and mortality in older adults in western USA from 2000 to 2013: a retrospective study.Lancet Planet Health. 2017; 1: e17-e25Summary Full Text Full Text PDF PubMed Scopus (40) Google Scholar published in The Lancet Planetary Health is the first to systematically analyse the risk of hospital admissions and mortality associated with drought periods in the USA. As the authors state, this is an understudied topic, but of great concern in the USA and globally as climate change is expected to worsen the severity and frequency of droughts in various regions. The Article breaks new ground by using US Medicare hospital admissions data and death certificates to assess changes in daily risk of cardiovascular-related and respiratory-related hospital admissions and mortality during periods of drought as measured by the US Drought Monitor. Its findings of increased mortality during periods of high severity worsening drought and decreased respiratory admissions during periods of full drought open the discussion about how drought affects health and just how severe and significant those effects are. One area that remains to be investigated is what measures or characteristics of drought are most predictive of health effects? Berman and colleagues discuss the complexity of this question, noting that there are 150 different drought measures in the scientific literature. For their study, the authors compared days of two different severity classes of drought and noted when the US Drought Monitor was progressively worsening for a given county. Unexplored dimensions in the present study include droughts of different duration or repetition; droughts in desert regions versus droughts in agricultural or more temperate regions; health-related exposures that occur as dry regions experience heavy rainfall and come out of drought; and droughts in areas that experience them most frequently. The authors chose to control for start season of the drought in their analysis but do not report whether droughts that started at different times of year had different health effects. This would be of some interest as well. Lastly, because the authors were using counties as their own comparison for drought versus non-drought periods, they chose to eliminate counties with a frequency of drought versus non-drought days of 1:1 or greater. This precluded analysis of the health effects for those counties with the highest frequency of drought, which could enhance understanding of magnitude and mechanisms of impacts. Future studies might explore comparison of multiple drought exposure methods and models, similarly to what has been done for heat.2Dong W Zeng Q Ma Y Li G Pan X Impact of heat wave definitions on the added effect of heat waves on cardiovascular mortality in Beijing, China.Int J Environ Res Public Health. 2016; 13: 933Crossref Scopus (22) Google Scholar, 3Kent ST McClure LA Zaitchik BF Smith TT Gohlke JM Heat waves and health outcomes in Alabama (USA): the importance of heat wave definition.Environ Health Perspect. 2014; 122: 151-158Crossref PubMed Scopus (1) Google Scholar, 4Smith TT Zaitchik BF Gohlke JM Heat waves in the United States: definitions, patterns and trends.Clim Change. 2013; 118: 811-825Crossref PubMed Scopus (195) Google Scholar Another question clearly not answered by this study is what are the health effects of drought in people younger than 65 years, including susceptible populations like outdoor workers and children? Although the population aged 65 years and older will include some active and working individuals, the use of Medicare data makes these susceptibility factors and other populations difficult to assess. Finally, the study's approach of using a daily time series to analyse respiratory-related and cardiovascular-related hospital admissions and all-cause mortality at the county level has limited the types of health effects that can be assessed. The daily time series is a good method for observing small changes in high frequency health events, but is not as good at observing moderate increases in rare events. As such, the associations between drought and specific causes of mortality, and other types of diseases and injuries, especially the variety of infectious diseases that have been associated with drought and rainfall in other regions, remain to be investigated. As a useful pioneering study should, the study by Berman and colleagues raises and helps define more questions than it answers. With Earth observations indicating increasing variability in precipitation patterns around the globe, the need to understand the health effects of drought is as great as the need to understand the health effects of flooding and extreme precipitation. This study confirms that severe drought is associated with harm to human health and helps identify useful directions for future research. I declare no competing interests. Drought and the risk of hospital admissions and mortality in older adults in western USA from 2000 to 2013: a retrospective studyDrought conditions increased risk of mortality during high-severity worsening drought, but decreased the risk of respiratory admissions during full drought periods among adults aged 65 years and older. Counties that previously had fewer drought events show larger risk for mortality and cardiovascular disease. This research describes an understudied environmental association with global health significance. Full-Text PDF Open Access