In regions with limited vegetation and low rainfall variability, the findings offer a global perspective on how extreme rainfall events impact health.
A new analysis published in The BMJ reveals that extreme rainfall events are linked to a heightened risk of death from various causes, including heart and lung diseases. This study, which examined data from 34 countries and regions, found that the health impacts of extreme rainfall differ based on local climate and vegetation coverage, offering a comprehensive global view on how these weather events influence health outcomes.
Climate change is intensifying the frequency and severity of short-term rainfall events, and emerging evidence suggests a compelling link between rainfall events and adverse health outcomes, particularly transmission of infectious diseases.
But the influence of rainfall events on cardiovascular and respiratory health, and how varying rainfall intensities affect these conditions, remains understudied.
To address this, researchers set out to examine the associations between daily rainfall (intensity, duration, and frequency) and all-cause, cardiovascular, and respiratory deaths. They analyzed daily mortality records and rainfall data from 645 locations across 34 countries or regions on six continents, comprising a total of 109,954,744 all-cause, 31,164,161 cardiovascular, and 11,817,278 respiratory deaths from 1980 to 2020.
The main measure of interest was the association between daily deaths and rainfall events with return periods (expected intervals between events) of one year, two years, and five years.
Factors that might affect this association, such as local climate type, rainfall variability, and vegetation coverage, were also taken into account.
Key Findings: Impact of Extreme Rainfall Events
During the study period, a total of 50,913 rainfall events with a one-year return period, 8,362 events with a two-year return period, and 3,301 events with a five-year return period were identified.
Overall, across all locations, a day of extreme rainfall with a five-year return period was associated with an 8% increase in all-cause deaths, a 5% increase in cardiovascular deaths, and a 29% increase in respiratory deaths over a 14-day period after the rainfall event.
Extreme rainfall events with a two-year return period were associated with respiratory deaths only, whereas rainfall events with a one-year return period showed no effect on either cardiovascular or respiratory deaths. Locations with lower variability of rainfall or scarce vegetation coverage showed higher risks of deaths after extreme rainfall events.
Further analysis showed protective effects of moderate to high rainfall, possibly due to reduced air pollution and people staying indoors. But risk of harm increased at extreme rainfall levels, likely due to damage to infrastructure, water contamination, and exposure to harmful microorganisms.
Study Limitations and Implications for Public Health
These are observational findings, so no firm conclusions can be drawn about causality, and the authors acknowledge that analyzed locations were mainly in east Asia, Europe, and North America, and individual factors such as age, sex, race, urban/rural residence, or specific clinical settings were not captured.
However, they say these findings underscore the need for coordinated public health strategies to mitigate the broad health effects of extreme rainfall. “This is especially important considering the well-established trend of increasing short-term rainfall intensity as a result of climate change,” they add.
In a linked editorial, John Ji at Tsinghua University in China welcomes the study and says health professionals are ideally placed to drive climate action by educating patients about climate-related health risks and fostering resilience within communities.
Yet, despite the clear science, he acknowledges that climate action remains difficult.
“People often forget the lessons of scarcity during times of abundance—a risky form of amnesia for climate change,” he notes. “The stakes are far too high, for when it rains, it pours—and in this era of escalating climate extremes, it will pour harder than ever before.”
Reference: “Rainfall events and daily mortality across 645 global locations: two stage time series analysis” by Cheng He, Susanne Breitner-Busch, Veronika Huber, Kai Chen, Siqi Zhang, Antonio Gasparrini, Michelle Bell, Haidong Kan, Dominic Royé, Ben Armstrong, Joel Schwartz, Francesco Sera, Ana Maria Vicedo-Cabrera, Yasushi Honda, Jouni J K Jaakkola, Niilo Ryti, Jan Kyselý, Yuming Guo, Shilu Tong, Francesca de’Donato, Paola Michelozzi, Micheline de Sousa Zanotti Stagliorio Coelho, Paulo Hilario Nascimento Saldiva, Eric Lavigne, Hans Orru, Ene Indermitte, Mathilde Pascal, Patrick Goodman, Ariana Zeka, Yoonhee Kim, Magali Hurtado Diaz, Eunice Elizabeth Félix Arellano, Ala Overcenco, Jochem Klompmaker, Shilpa Rao, Alfonso Diz-Lois Palomares, Gabriel Carrasco, Xerxes Seposo, Susana das Neves Pereira da Silva, Joana Madureira, Iulian-Horia Holobaca, Noah Scovronick, Fiorella Acquaotta, Ho Kim, Whanhee Lee, Masahiro Hashizume, Aurelio Tobias, Carmen Íñiguez, Bertil Forsberg, Martina S Ragettli, Yue Leon Guo, Shih-Chun Pan, Samuel Osorio, Shanshan Li, Antonella Zanobetti, Tran Ngoc Dang, Do Van Dung and Alexandra Schneider, 9 October 2024, BMJ.
DOI: 10.1136/bmj-2024-080944
The study was funded by the Alexander von Humboldt Foundation.
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