Urban areas around the world are grappling with the impacts of extreme weather, and Mumbai, India, is a prominent example of the challenges posed by heavy rainfall and flooding. The city’s monsoon season brings not only torrential downpours but also significant public health risks, which remain insufficiently understood.
A pivotal study conducted by researchers from Princeton University and the University of Chicago has shed new light on the severe health risks associated with rainfall and rising sea levels in Mumbai. The study reveals that the mortality rate linked to these factors is nearly ten times higher than what official records indicate.
Monsoon Season in Mumbai
Mumbai experiences intense heavy rainfall during the monsoon season, from June to September. This megacity, situated between the Arabian Sea and the Western Ghats, can receive over 300 mm (11.8 inches) of rain in a single day. A notable instance was the Maharashtra floods in 2005, where Mumbai recorded an unprecedented 944 mm (37.2 inches) of rainfall, causing massive destruction and over 1,000 fatalities.
Tom Bearpark, a co-first author and STEP Ph.D. student, stated, “Mumbai is one of the world’s largest and fastest growing cities. Each year, torrential monsoon season rains cause widespread disruption, closing roads, damaging infrastructure, and endangering lives.”
Linking Rainfall to Mortality
Researchers employed an innovative approach by combining high-resolution datasets, which included individual death records and sub-daily rainfall data from the Municipal Corporation of Greater Mumbai (MCGM), covering the monsoon seasons from 2006 to 2015. They matched each death with local rainfall data using residential addresses and classified residents as “slum” or “non-slum” based on census information.
To assess the mortality impact, the team used an econometric model that accounted for both immediate and delayed effects of rainfall, considering age, gender, and residential status. The model also evaluated how tide height influences the health impacts of rainfall, with Bearpark noting, “We developed a model which allows the impacts of rainfall to differ based on the level of the tide during the hour in which the rain fell.”
Revealing Stark Inequalities
The study’s results highlight significant disparities. Rainfall contributes to more than 8% of deaths during the monsoon season in Mumbai, a figure nearly tenfold higher than official statistics. Slum residents account for over 80% of these deaths, and for children under five, 18% of monsoon-related deaths are due to rainfall. Women are found to be at higher risk compared to men.
Bearpark emphasized, “Our results illustrate a deep inequality in the impacts of extreme weather and future climate change, with poorer areas facing disproportionate damages.”
Climate change is expected to exacerbate this situation. A sea level rise of just five centimeters could increase rainfall-induced deaths from 8.5% to 9.1% of total deaths. A rise of 15 centimeters could elevate this to 10%, marking a 21% increase.
Lessons for Global Cities
The implications of this study extend beyond Mumbai, offering crucial insights for cities worldwide. The authors stress the need for investments in water infrastructure, sanitation, waste management, and drainage systems to mitigate the mortality risks posed by rainfall.
Ashwin Rode, co-first author and Director of Scientific Research at the University of Chicago’s Energy Policy Institute, stated, “While our study reveals that rainfall and flooding pose major public health challenges, it also points to the value of targeted investments in sanitation, clean water, waste management, and drainage systems in saving lives and reducing inequality.”
“Climate change is already bringing intensified rainfall and rising sea levels worldwide. The time to make these investments is now.”
More information: Tom Bearpark et al, Mortality impacts of rainfall and sea-level rise in a developing megacity, Nature (2025). DOI: 10.1038/s41586-025-09730-4
Original Story at phys.org