Floods Are Deadly for Months After Water Recedes, Study Finds

The deadly consequences of flooding on human health lasts weeks longer then the floods themselves, according to a new study published on Monday.

The research found that people caught in floods have a higher risk of dying from all causes, and in particular from cardiovascular and respiratory issues, for as many as 60 days afterward. The finding has major implications in a warming world where flooding will continue to get worse.

"Do mortality risks change after floods in the general population? The answer is yes, and this needs to be factored into policy responses to flooding events," said Yuming Guo, a professor at Monash University in Australia and co-lead author of the new study, according to a press release.

How floods kill

Guo and his colleagues examined data from 761 communities in 34 countries that had experienced at least one flood between 2000 and 2019. They then reviewed a total of 47.6 million deaths from any cause, and calculated what proportion of the deaths can be attributed to the floods.

Guo and his team found that the risk of dying went up after a flood, and that increase persisted for up to 60 days; for cardiovascular deaths in particular, the spike persisted for 50 days. In total, the number of deaths went up by 2.1% on average, but cardiovascular deaths increased 2.6%, while respiratory deaths went up 4.9%.

Somewhat shockingly, the peak in mortality risk occurred at about 25 days after the flood, the researchers found.

The reason why death rates go up after a flood is likely down to a number of factors: The water often carries deadly pathogens, such as bacteria or fungi, and it can contaminate food and drinking water sources. At the same time, floods can block a sick person's path to hospital, or cause so much stress that the person misses warning signs until it is too late.

Will floods be more dangerous in future?

The findings suggest that climate change could make floods even deadlier than previously anticipated. Aside from coastal flooding thanks to sea level rise, major precipitation events — like the one that inundated New York City last weekend — are becoming more common thanks to the warmer atmosphere's ability to hold more moisture.

Researchers at the World Bank estimated last year that more than 1.8 billion people around the world were facing significant flood risk, and almost 90% of those are in low- and middle-income countries. "Climate change and risky urbanization patterns are expected to further aggravate these risks in coming years," they wrote in a recent study.

In turn, Guo and his team said that healthcare providers need to be on high alert after a flood.

"They should incorporate this knowledge into their practice and be prepared for the suddenly elevated demands of health services to reduce avoidable deaths from natural causes," Guo said.