Evaluation of the Impacts of Repetitive Flood Exposure on Mortality Rates in North Carolina

Flooding adversely impacts human health, contributing to higher population-level mortality rates. While past qualitative studies have shown that repetitive exposure exacerbates mortality, few studies have attempted to quantitatively evaluate the effect of repetitive flood exposure on mortality rates at a population-level. This ecologic longitudinal study sought to evaluate the impact of repetitive flood exposure in North Carolina on rates of mortality between 2002 and 2019 using county-level negative binomial linear regression. The study population included 1,012,765 North Carolina Vital Records death records from the state’s 70 eastern-most counties between 2002 and 2019 with sub-analyses examining cardiovascular- (n = 293,701), cancer- (n = 232,936), and suicide-specific (n = 12,153) mortality. Counties’ annual exposure to flooding was characterized based on three definitions (number of events, maximum event severity, and cumulative event severity) derived from modeled flood extent data. Effects on annual county-level mortality rates were analyzed. Results show that the number of flooding events had no significant impact on mortality rates, while both severity definitions had minor positive effects, indicating severity may be a key component of repetitive exposure effects. The presence of FEMA Individual Assistance triggers had a protective effect on suicide mortality rates, and counties with older populations had increased rates of mortality compared to those with younger populations. While none of the exposure definitions portrayed a clear or consistent relationship between repetitive flooding and mortality, this study indicates the need for more nuanced analyses of repetitive exposure and for policy targeting adverse mental health outcomes following flood events, particularly for older populations.