Flood fatalities: Experts reveal the hidden health impacts

A new study has shown that over the last 20 years, large floods in the U.S. have been linked with significantly higher death rates across major causes of mortality. 

Published in the journal Nature Medicine, this research highlights sweeping and hidden effects of floods – including those not related to hurricanes, such as those resulting from heavy rain, snowmelt, or ice jams – on public health.

Bridging a critical knowledge gap

The study was led by scientists at Columbia University Mailman School of Public Health, in partnership with researchers from Arizona State University, Harvard University, and the University of Arizona. 

The experts aimed to fill a crucial gap in understanding cause-specific mortality risks related to floods over time and how these risks vary among different groups. The findings are expected to help public health agencies better allocate resources to mitigate these risks.

In the United States, population growth alone is believed to result in an approximately 72 percent increase in the population exposed to floods yearly by 2050. This is before accounting for the impact of climate change, which will likely lead to more frequent river, coastal, and flash floods.

Flooding is an urgent public health concern 

Victoria Lynch, a post-doctoral research fellow at Columbia Mailman School and the study’s first author, stressed the severity of the issue. 

“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 said. 

“Our results show that floods were associated with higher death rates for most major causes of death, even for rain- and snow-related floods that are less likely to generate rapid emergency responses.”

Study senior author Robbie M. Parks, assistant professor in Environmental Health Sciences at Columbia Mailman School, noted that floods have a devastating effect on society in the U.S., yet a comprehensive assessment of their continuing health impacts had been lacking.

“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,” said Parks. 

Deaths after large floods

The research team examined 35.6 million U.S. death records spanning from 2001 to 2018. Using a statistical model, they compared death rates during three-month periods following large floods to those during normal conditions, assessing variations across 2,711 counties that cover over 75% of the U.S. population.

The analysis revealed significant increases in death rates associated with flooding:

• Injury deaths: Tropical storm and hurricane-related floods caused a 24.9% increase in deaths among older adults and a 21.2% rise among women.
• Cardiovascular diseases: Death rates rose by 2.1% during heavy rain floods and 8.9% during snowmelt-related floods.
• Respiratory diseases: Snowmelt-related flooding was linked to a 22.3% increase in mortality.
• Neuropsychiatric conditions: Death rates rose by 15.9% during snowmelt-related floods.
• Infectious diseases: Heavy rain floods caused a 3.2% increase in deaths, likely due to disruptions to water and sewage systems.

The study noted an alarming increase in the frequency of record-breaking rainfall. For instance, record-high monthly rainfall totals were achieved 27 percent more frequently in 2024 than at the century’s start, while daily records rose by 52 percent.

Lingering health impacts of floods

The experts emphasize that floods cause long-lasting health impacts beyond the immediate disaster. Extreme rainfall events led to widespread flash floods in regions such as Afghanistan, Pakistan, Spain, and Bangladesh, causing thousands of deaths and widespread displacement. 

Conversely, severe drought conditions in places like the Amazon and southern Africa disrupted ecosystems, reduced crop yields, and heightened wildfire risks.

“Our study shows that even floods caused by snowmelt or heavy rain, each uniquely driven by changes to climate and development, elevate mortality months after the fact, providing critical knowledge of how to manage and adapt to floods,” said study co-author Jonathan Sullivan, an assistant professor at the University of Arizona.

These findings call for urgent action, including stronger flood defences, drought-resilient agriculture and water supplies, and better early warning systems. 

Understanding the broad and lasting health impacts of floods will be critical for building resilient communities in the face of climate change.

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