Floods and their health effects: disease risk persists for months

Floods are not only about immediate threats and evacuations—they also significantly increase the risk of illness. According to the largest global study of its kind, published in the journal Nature Water, the health effects of floods can last up to seven months after the waters recede, with consequences serious enough to require hospitalization.

Flooding and increased hospitalization risk within 210 days

A team of researchers from Monash University in Melbourne analysed hospital data from 747 communities across eight countries: Australia, Brazil, Chile, Canada, New Zealand, Taiwan, Thailand, and Vietnam. Their analysis covered not only the immediate health consequences of flooding—such as drowning or injuries—but, more importantly, the long-term effects. In total, the study reviewed 300 million hospitalization cases recorded over two decades.

Using mathematical models and historical flood data, the researchers found that the risk of hospitalization remains, on average, 26% higher for up to 210 days after the floodwaters recede. This increased risk is attributed not only to contamination of local water sources, but also to ideal conditions for the spread of fungi, bacteria, and viruses. Post-flood areas may also face increased health threats due to the spread of mosquitoes, cockroaches, and rodents.

Surprising health consequences of flooding

An in-depth analysis of hospital records allowed the Australian researchers to identify specific medical risks associated with flooding. The findings are somewhat unexpected and reveal that the full scale of flood health consequences is much broader than previously thought.

Within seven months of floodwaters receding, local communities face a 35% higher risk of hospitalization due to cardiovascular diseases and injuries. The risk of hospital admissions related to respiratory and digestive diseases increases by 30%, while diabetes-related hospitalizations rise by a staggering 61%—not necessarily due to new cases, but often because of worsened conditions in existing patients (e.g., due to treatment interruptions or lack of access to medications). An increased risk of hospitalization is also observed for infectious diseases within the first 90 days after a flood, and for mental health disorders within the first 150 days.

The researchers also found that the health effects of floods are more pronounced among children and youth under 20, as well as seniors over 60. Interestingly, higher hospitalization rates were observed in more socioeconomically developed regions. The authors suggest this might be due to limited access to healthcare in less developed areas, which could lead to underreporting.

Why is this important?

According to study lead Prof. Yuming Guo, climate change is likely to bring more frequent, intense, and prolonged floods. Currently, over 1.8 billion people—about 23% of the global population—live in flood-prone areas. This should serve as a wake-up call for national and regional authorities.

Floods are not just about destructive waves and increased risk of infectious disease outbreaks. Flooded homes, evacuations, poor hygiene conditions, and overwhelmed healthcare systems contribute to an overall decline in public health. The situation is especially critical for people with chronic conditions who depend on regular treatments such as dialysis, chemotherapy, or specific medications that may become inaccessible.

Prof. Guo’s team urges policymakers to account for the wide-ranging health effects of flooding when planning and managing public services. Hospitals and clinics must prepare not only for immediate aftermaths but for elevated hospitalization risks and complications that may last for up to six months post-flood.