Climate change and rising sea levels to worsen urban health risks in Mumbai

Rainfall and flooding frequently disrupt the lives of urban dwellers around the world, posing significant public health risks. Mumbai, India, renowned for the ferocity of its monsoon season, provides a stark example of the human toll that extreme urban flooding can take. But despite the growing recognition and urgency of these risks, the health impacts of precipitation remain poorly understood, and those of sea level rise are completely 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, revealing that deaths caused by rainfall and sea level rise are nearly ten times higher than official statistics suggest.

The results are published in the journal Nature.

Monsoon season in Mumbai

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

One of the most infamous examples is the 2005 Maharashtra floods, which caused catastrophic flooding in Mumbai. During this flood, the city received record rainfall of 944 mm (37.2 inches), resulting in more than 1,000 deaths, hundreds of millions of dollars in damage, and the forced evacuation of hundreds of people.

“Mumbai is one of the largest and fastest growing cities in the world,” says co-first author and STEP doctoral student. student Tom Bearpark. “Every year, torrential monsoon rains cause widespread disruption, closing roads, damaging infrastructure and putting lives at risk. »

How Researchers Linked Rainfall to Mortality

Drawing on a unique combination of high-resolution datasets, the researchers linked individual death records to 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 compared to highly localized rainfall measurements using residential addresses and classified as “slum” or “non-slum” residents based on the lists of census.

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 residency status. They also developed a new method that estimates the mortality impacts of hourly rainfall while accounting for tide height, a crucial factor for a coastal city like Mumbai.

“We developed a model that can differentiate the impacts of precipitation based on the tide level during the time the rain fell,” says Bearpark. “This model allows us to quantify how sea level rise could amplify the health impacts of precipitation in the future.”

Key findings reveal deep inequalities

The findings are sobering. The results showed that rainfall is responsible for more than 8% of deaths during Mumbai’s monsoon season, an estimate almost 10 times higher than official statistics.

Slum dwellers were predominantly represented in monsoon deaths, accounting for more than 80% of rainfall-related deaths. Among children under five, 18% of deaths were attributed to rainfall during the monsoon. The study also found that women face higher risks than men.

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

Researchers warn that climate change risks making this crisis worse. Even a slight rise in sea level of five centimeters – an already plausible change by 2030 – could increase the share of mortality caused by precipitation from 8.5% to 9.1% of total deaths, an increase of 7%. With a sea level rise of 15 centimeters, precipitation-related deaths could reach 10% of total deaths, an increase of 21%.

These sea level changes are minimal compared to projections for Mumbai by 2050, underscoring how even modest sea level increases can significantly increase rainfall-induced health risks in low-lying, densely populated cities.

Lessons for cities around the world

Beyond its implications for Mumbai, this study offers essential lessons for cities around the world. The authors highlight the importance of investing in water infrastructure, sanitation, waste management and drainage systems to combat rainfall-related mortality.

The authors also call for an urgent expansion of climate impact assessments that go beyond temperature-related mortality and consider the health risks posed by precipitation and sea level rise.

“While our study finds that precipitation and flooding pose major public health problems, it also highlights the value of targeted investments in sanitation, drinking water, waste management, and drainage systems to save lives and reduce inequality,” says co-first author Ashwin Rode, director of research science at the University of Chicago’s Energy Policy Institute.

“Climate change is already causing increased precipitation and rising sea levels around the world. Now is the time to make these investments.”