Assessment of Potential Health Impacts from Extreme and Exceptional Drought, 2012−16

Drought is a natural phenomenon that contributes to an array of adverse physical and mental health outcomes. Populations are more vulnerable to the health effects of drought due to a number of factors, including socioeconomic status and reliance on agriculture for livelihoods. Quantifying the duration and severity of drought in the United States in relation to characteristics that make populations more vulnerable can help to prioritize public health interventions to mitigate the potential adverse health effects of drought in the most impacted locations. CDC’s National Environmental Public Health Tracking Program has collaborated with the Cooperative Institute for Climate and Satellites – North Carolina (CICS-NC) to make drought index data from the National Oceanic and Atmospheric Administration’s (NOAA) National Centers for Environmental Information available to the public through its National Environmental Health Tracking Network. Trends in extreme and exceptional drought were assessed at the county level for the period of 2012-2016 using two distinct data sources: the Standardized Precipitation Evapotranspiration Index (SPEI) and the United States Drought Monitor (USDM). One index for each data source was created to identify counties with the highest vulnerability to health impacts stemming from the most severe forms of drought. These indices incorporated data measuring drought duration and severity as well as measures of drought susceptibility: percent population under five years of age, percent of population aged 65 or older, percent of population living in poverty, percent of small or very small community water systems, percent of non-coastal water area, and percent of cultivated crop land use. Percentile rankings for each variable were summed into exposure and susceptibility components that were multiplied to compute an overall index score, the results of which were ranked nationally for all counties in the contiguous United States. The resulting indices were mapped in ArcGIS and analyzed using Local Indicators of Spatial Autocorrelation (LISA) analyses to identify clusters of high potential risk. Approximately three quarters of counties in the contiguous United States experienced extreme drought (SPEI) during the study period, while around one third experienced exceptional drought (USDM). Counties identified as vulnerable by the two indices varied spatially, with highly vulnerable counties spread more evenly across the country based on the SPEI index. When the most vulnerable counties from each index were overlayed, distinct zones of high vulnerability to health effects of severe drought were evident in the western, central, and southeastern parts of the country. This pattern was also demonstrated through bivariate LISA analysis of high SPEI and USDM index values. The majority of vulnerable counties, especially among those identified as vulnerable by both indices, were located in rural areas that may lack the resources to adapt and respond to drought. Interventions to build capacity for drought adaptation and response should be ongoing in the identified vulnerable counties, particularly those in rural areas.