Climate change and rising sea levels to worsen urban health risks in Mumbai, study co-led by Princeton and University of Chicago reveals

Rainfall and flooding frequently disrupt the lives of urban residents worldwide, posing significant public health risks. Mumbai, India - renowned for the ferocity of its monsoon season - stands as a stark example of the human toll that extreme urban flooding can exact. But despite the growing recognition and urgency of these hazards, the health impacts of rainfall remain poorly understood, and those of sea level rise are entirely unquantified.  

A recent study led by Princeton University and the University of Chicago takes a closer look at the intersection between climate change, hazards, and public health in Mumbai, finding that deaths caused by rainfall and rising sea levels are almost ten times higher than the official statistics suggest.  

Background: Monsoon Season in Mumbai

Mumbai is known for its heavy rainfall during the June to September monsoon season.  Located between the coast of the Arabian Sea and the foothills of the Western Ghats mountain range, Mumbai’s climate leads to the city receiving a significant amount of rainfall, with some days bringing more than 300 mm (11.8 inches) of rain.  

One of the most infamous examples is the Maharashtra floods of 2005, that caused a catastrophic level of flooding in Mumbai.  During this flood, the city received a record-breaking 944 mm (37.2 inches) of rainfall, leading to over 1,000 deaths, hundreds of millions of dollars in damages, and the forced evacuation of hundreds of people.  

“Mumbai is one of the world’s largest and  fastest growing cities,” says co-first author and STEP Ph.D. student, Tom Bearpark.  “Each year, torrential monsoon season rains cause widespread disruption, closing roads, damaging infrastructure, and endangering lives.”

The Data and Methods

Drawing on a unique combination of high-resolution datasets, the researchers linked individual death records with sub-daily rainfall data from the Municipal Corporation of Greater Mumbai (MCGM), encompassing the city’s monsoon seasons from 2006 to 2015. Each death was matched with highly localized rainfall measures using residential addresses and categorized as “slum” or “non-slum” residents based on census lists. 

The team then used an econometric model that captures both the immediate and delayed effects of rainfall on mortality in each of Mumbai’s 89 PIN (i.e., postal) codes, allowing the impact to vary by age, gender, and residential status. They also developed a new method that estimates the mortality impacts of hourly rainfall whilst accounting for  tide height, a crucial factor for a coastal city like Mumbai.

“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,” explains Bearpark.  “This model allows us to quantify how rising sea levels could amplify the health impacts of rainfall in the future.”

The Results

The findings are sobering. The results showed that rainfall accounts for more than 8% of deaths during the monsoon season in Mumbai - an estimate that is almost 10 times that of official statistics.  

Slum residents were overwhelmingly represented in monsoon deaths, representing over 80% of rainfall-induced mortality.  Among children under five, 18% of deaths were attributed to rainfall during the monsoon period.  The study also found that women face higher risks than men.  

“Our results illustrate a deep inequality in the impacts of extreme weather and future climate change, with poorer areas facing disproportionate damages,” says Bearpark.  “Differences in drainage, sanitation, and access to healthcare and resources vary greatly within cities, leading to extremely unequal impacts.”

The researchers warn that climate change will likely worsen this crisis. Even a modest sea level rise of 5 centimeters - a change already plausible by 2030 - could increase the share of mortality caused by rainfall from 8.5% to 9.1% of total deaths, a 7% increase. Under 15-centimeters of sea level rise rainfall-related deaths could reach  10% of total deaths, representing a 21% increase. These changes in sea-level are small compared to projections for Mumbai by 2050, underscoring how even modest increments of sea level rise can significantly increase rainfall-induced health risks in low-lying, densely populated cities.

The Implications

Beyond its implications for Mumbai, this study offers vital lessons for cities across the world. The authors emphasize the importance of investing in water infrastructure, sanitation, waste management, and drainage systems when combating rainfall mortality.  

The authors also call for an urgent expansion of climate impact assessments that move beyond the focus of temperature-related mortalities and account for the health risks posed by rainfall and sea level rise.  

"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,” explains co-first author Ashwin Rode, the Director of Scientific Research at the University of Chicago’s Energy Policy Institute.  “Climate change is already bringing intensified rainfall and rising sea levels worldwide.  The time to make these investments is now."

The paper, “Mortality consequences of rainfall and sea level rise in a developing megacity,” was published in Nature on November 12th, 2025.  The authors include Thomas Bearpark (School of Public and International Affairs, Princeton University), Ashwin Rode (Institute for Climate and Sustainable Growth, University of Chicago), and Archana Patankar (Green Globe Consulting, Mumbai, India).  This research was supported by Princeton University’s Center for Policy Research on Energy and the Environment and the Department of Economics at the University of Chicago.