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The findings come as Mumbai and several other Indian cities grapple with heatwave-like conditions and growing concerns over the impact of climate change on urban infrastructure and public health.

The study projects that Mumbai’s summer maximum temperature will rise to 39°C by 2040. According to the India Meteorological Department (IMD), the city’s normal summer temperature is around 34°C, indicating an increase of nearly 5°C above present levels.

The report also projects that Mumbai’s annual maximum temperature will rise to 33.1°C by 2040, an increase of 0.9°C from the baseline average. Summer wet-bulb temperatures and winter minimum temperatures are each expected to increase by 1.3°C over the same period.

Wet-bulb temperature is a measure that combines heat and humidity and indicates how effectively the human body can cool itself through sweating. Higher wet-bulb temperatures increase the risk of heat stress and heat-related illnesses.

“At present, Mumbai is witnessing a slew of activities related to infrastructure development. This is leading to a rise in concrete cover, which is perpetuating the heat-island effect, leading to increased temperature and humidity,” Santanu Goswami, Associate Director at the School of Climate Change and Sustainability, Azim Premji University, said while presenting the report.

Alongside rising temperatures, the study predicts a substantial increase in rainfall intensity. Mumbai is expected to witness nearly six additional days of heavy rainfall annually, while average monsoon rainfall could rise from the current 1,749 mm to 2,049 mm by 2040.

Researchers said the changing weather patterns are already affecting livelihoods across the region.

The projections are in line with trends observed in Brihanmumbai Municipal Corporation (BMC) data, which shows a rise in the intensity of very heavy rainfall events over recent years.

As per IMD classifications, rainfall between 64.5 mm and 115.5 mm in 24 hours is categorised as heavy rainfall, 115.6 mm to 204.4 mm as very heavy rainfall, and more than 204.5 mm as extreme rainfall.

According to BMC data, the average volume of very heavy rainfall recorded within a 24-hour period has increased from 132 mm to 182 mm over the past six years.

The civic body’s records also show that Mumbai witnessed 28 episodes of prolonged very heavy rainfall lasting four hours or more during the last decade.

While Mumbai records more than 100 mm of rainfall on an average of 16 days every year, the city crossed or matched that mark in five years between 2016 and 2024 in 2017, 2018, 2019, 2021, and 2024.

The data further indicates an increase in the frequency of intense rainfall events. Between 2021 and 2024, Mumbai recorded 66 days with rainfall exceeding 100 mm, compared to 52 such days between 2018 and 2020.

The study warns that these shifts could have far-reaching consequences for coastal (Koli) communities and urban infrastructure. The Koli communities in Maharashtra are traditionally into fishing.

“The Koli community in Mumbai reports business losses when unpredictable rain spells disrupt the traditional drying of prawns. By focusing on the immediate 2040 window, it is important for the West Coast to safeguard its infrastructure and unique coastal heritage,” the report stated.