In the past two decades, significant flooding events in the U.S. have been linked to death rates from major causes of mortality being up to 24.9 percent higher than under normal conditions. A recent study published in Nature Medicine highlights the extensive and often unnoticed impacts of floods, including those not resulting from hurricanes, like floods triggered by heavy rainfall, melting snow, or ice jams.
The research, spearheaded by scientists from the Columbia University Mailman School of Public Health, also included collaborators from Arizona State University, Harvard University, and the University of Arizona.
Prior to this study, there was a significant lack of understanding concerning the specific mortality risks associated with flooding in the U.S. over time, and how these risks differ across various population groups. The findings from this research can assist public health agencies in distributing resources more effectively.
With U.S. population growth alone predicted to cause a 72 percent rise in the number of individuals exposed to floods each year by 2050, this projection does not even consider the additional risks posed by climate change, which is expected to increase the frequency of river, coastal, and flash flooding.
According to Victoria Lynch, PhD, the study’s lead author and a post-doctoral research fellow at Columbia Mailman School, “Floods are becoming an urgent public health issue as rising sea levels, rapid melting of snowpack, and more severe storms will likely result in more frequent and damaging flooding events. Our findings reveal that floods correlate with higher death rates across most major causes of death, including floods driven by rain and snow, which are less likely to trigger immediate emergency responses.”
Robbie M. Parks, an assistant professor in Environmental Health Sciences at Columbia Mailman School and senior author, remarked, “While floods have a catastrophic impact on communities in the U.S., there has been a lack of thorough assessments of their persistent health effects. Our research is a significant first step in enhancing our understanding of how floods contribute to mortality, forming a crucial basis for enhancing resilience against climate-related disasters in the days, weeks, months, and years following such events.”
Researchers analyzed 35.6 million death records from the U.S. from 2001 to 2018 and applied a statistical model to observe changes in death rates during three-month periods following significant flooding as compared to similar periods in non-flood conditions.
Residents across 2,711 counties, encompassing over 75 percent of the U.S. population, endured at least one major flood during the study. The primary cause of these large flooding events was heavy rainfall, followed by snowmelt in the Midwest and tropical cyclones in the southeast.
The study revealed the most significant increases in injury mortality rates among older adults (24.9 percent) and women (21.2 percent) during periods of flooding related to tropical storms or hurricanes. Increases in death rates linked to heavy rain-induced floods were noted for infectious diseases (3.2 percent) and cardiovascular diseases (2.1 percent). Snowmelt flooding was associated with escalated death rates from respiratory diseases (22.3 percent), neuropsychiatric conditions (15.9 percent), and cardiovascular diseases (8.9 percent).
The rise in infectious diseases is likely due to disruptions in clean water and sewage systems that can trigger waterborne diseases. Chronic and neuropsychiatric issues may stem from the stress caused by ongoing disruptions related to flooding. Furthermore, socioeconomic factors influencing health outcomes in flood-prone communities, as well as how effectively residents can evacuate and recover after emergencies, are also critical considerations.
Jonathan Sullivan, an assistant professor in Geography, Development, and Environment at the University of Arizona and co-author, stated, “Most of our insights into flood-related health impacts have come from major disasters like Hurricane Katrina or Harvey, which, while devastating, represent just a portion of a larger issue. Our research indicates that even floods from snowmelt or heavy rainfall, each driven by shifts in climate and development, result in increased mortality long after the events, providing essential insights for managing and adapting to floods.”
Prior studies by the authors have uncovered a rise in death rates following tropical cyclones in the U.S., particularly among socially vulnerable communities of color, and have found that tropical cyclones are linked to the spread of waterborne diseases.
Other co-authors involved in the study include Aaron Flores from Arizona State University; Sarika Aggarwal and Rachel C. Nethery from Harvard Chan School of Public Health; and Marianthi-Anna Kioumourtzoglou, Anne E. Nigra, and Xicheng Xie from Columbia Mailman School of Public Health.
This research received support from the National Institute of Environmental Health Sciences through various grants (ES007322, ES033742, ES009089, AG093975, ES007142).
