気候変動：ムンバイにおける異常降雨に関連した不均衡な死亡率

Excess rainfall and flooding in the coastal megacity of Mumbai, India, could be responsible for approximately 8% of the city’s total deaths during monsoon season, according to a paper in Nature. Children, women and residents of slums are likely to be disproportionately affected. The findings highlight the importance of adequate infrastructure investments in growing urban areas.

Rainfall and flooding pose a threat to people living in urban areas, and inadequate infrastructure such as poor drainage can increase the impact of extreme weather events. As climate change continues and more people settle in flood-prone areas, understanding the relationship between rainfall, sea-level rise and public health is crucial.

Tom Bearpark and colleagues analysed death records and rainfall data in Mumbai from 2006 to 2015 to gauge the mortality rate following excess rainfall (for instance, days with 150mm rainfall) and flooding. They found that rainfall contributed to around 7.3–8.6% of deaths during an average monsoon season, which equated to around 2,308 to 2,718 lives lost per year. A day with 150mm rainfall causes a 2.2% increase in the general mortality rate in Mumbai across the subsequent 5 weeks, probably due to mechanisms including the spread of flood-related diseases, such as dengue, malaria and typhoid, in the wake of the storm.

The relative risk of increased mortality rates over the 5 weeks after a 150-mm rainfall event was highest in children under 5 years old (5.3%) relative to older individuals, and higher in women than in men (3.1% and 1.5%, respectively). More than 80% of the deaths associated with extreme rainfall occurred in people living in informal slum settlements. Differences in death rates following extreme rainfall during high and low tides were also estimated. The increase in the 5-week mortality rate caused by rainfall was lower when rain fell at low tide than at high tide, probably because higher tides reduce the capacity of drainage systems, the authors note.

The authors conclude that the findings highlight the urgent need for investment in improved drainage, sanitation and waste-management infrastructure in developing urban areas.

• Article
• Published: 12 November 2025

Bearpark, T., Rode, A. & Patankar, A. Mortality impacts of rainfall and sea-level rise in a developing megacity. Nature (2025). https://doi.org/10.1038/s41586-025-09730-4

News & Views: Extreme rainfall poses the biggest risk to Mumbai’s most vulnerable people
https://www.nature.com/articles/d41586-025-03453-2