A new study published in Nature Medicine has unveiled startling findings about the long-term effects of large floods on public health in the United States. Conducted by researchers from Columbia University’s Mailman School of Public Health, in collaboration with teams from Arizona State University, Harvard University, and the University of Arizona, the research shows a significant connection between floods and increased mortality rates from various causes, including injuries, infectious diseases, and other health complications.
The study spans a period of two decades, from 2001 to 2018, and reveals that large floods were associated with up to a 24.9 percent higher death rate from major causes compared to periods with normal conditions. Notably, these floods were not limited to hurricane-induced disasters but also included those caused by heavy rainfall, snowmelt, or ice jams. The research fills a crucial gap in understanding the hidden, long-term health impacts of floods that have often been overlooked in public health assessments.
Victoria Lynch, Ph.D., a postdoctoral research fellow at Columbia Mailman School and the first author of the study, explains, “Flooding is an urgent public health concern as sea level rise, rapid snowpack melting, and increased storm severity will lead to more destructive and frequent events.” She emphasizes that the study’s findings show how floods, including those triggered by rain or snow, contribute to rising mortality rates across multiple health categories. “Even those floods less likely to generate rapid emergency responses, such as those from rain or snowmelt, still lead to a concerning rise in deaths.”
The research utilized an extensive dataset, comprising 35.6 million death records from U.S. residents between 2001 and 2018. The researchers then employed a statistical model to analyze the changes in death rates over three-month periods following major flood events. These periods were compared to equivalent periods under normal conditions, allowing the team to isolate the effect of floods on mortality.
The study also highlights that more than 75 percent of the U.S. population lived in areas affected by at least one large flood during the research period. The most common causes of these floods were heavy rainfall, followed by snowmelt events in the Midwest and tropical cyclones in the southeast.
One of the most alarming conclusions from the research is the projected increase in flood exposure due to population growth and climate change. By 2050, it is estimated that the U.S. will see a 72 percent rise in the population exposed to floods annually. This increase does not even account for the expected surge in flood events due to climate change, including more frequent river, coastal, and flash floods. These changes make it even more crucial for public health authorities to address the risks posed by flooding and its lasting health impacts.
Robbie M. Parks, Ph.D., assistant professor of Environmental Health Sciences at Columbia Mailman School and the senior author of the study, stresses the importance of this research in filling a significant gap in flood health studies. He explains, “Our study is a first major step in better understanding how floods may affect deaths, which provides an essential foundation for improving resilience to climate-related disasters across the days, weeks, months, and years after they wreak destruction.”
As climate change accelerates and floods become more frequent and severe, this study underscores the urgent need for a more comprehensive approach to public health preparedness and response, not just during a flood, but in the months and years that follow. Public health agencies must consider the long-term consequences of floods on mortality, especially as more communities face the threat of rising waters in the future.
