Mumbai could become hotter, wetter and more humid by 2040, warns study

Extreme heat softens the road surface outside the BMC headquarters in Fort, leaving visible tyre impressions on the tar. Pic/Ashish Raje

Mumbai is projected to become significantly hotter, wetter and more humid by 2040, with residents likely to experience heat more intensely than what thermometers record due to rapid urbanisation, shrinking tree cover and increasing concreting, according to a new study by Azim Premji University.

The report, Indian Coastal Regions: Climate Projections 2021-2040, forecasts rising temperatures, increased humidity, more days above 40°C and nearly two additional weeks of heavy rainfall annually. The changes could have far-reaching consequences for public health, infrastructure, and livelihoods, particularly among vulnerable communities such as Kolis.

Heat rising from railway tracks creates a mirage-like effect as railway workers carry out maintenance work near Bandra station. Pic/Satej Shinde

Why Mumbai could feel hotter than the forecast

The study says actual human experience of heat will increasingly depend on neighbourhood-level urban conditions rather than citywide temperatures alone.

Factors that worsen heat
. Concrete roads
. Cemented footpaths
. Loss of tree cover
. Reduced green spaces
. High-rise buildings trapping heat
. Direct exposure to sunlight

These conditions create localised heat pockets, often referred to as urban heat islands.

Extreme weather to become more common

Hotter days
. Mumbai could see nearly two additional days every year with temperatures exceeding 40°C
. The warning comes months after Mumbai recorded its hottest March day in five years, touching 40°C this year - about 6°C to 7°C above the seasonal average; the previous instance was on March 28, 2021, when temperatures reached 40.9°C

More heavy rain days
The report projects:
. 12.4 more heavy rain days
. 42 days each monsoon season recording more than 20 mm rainfall. This translates into an extra week-and-a-half of intense rain every year.

Case study: Bandra's heat spike

In May this year, Bandra recorded a local temperature of 39°C while Mumbai's official temperature hovered between 34°C and 35°C.
According to the study, these local factors may have amplified the heat:

. Absence of large trees
. Extensive concretisation
. Cemented footpaths
. Reduced shade cover

The bigger concern: Warmer nights

The study says rising temperatures during nights and winters may have a greater impact than hotter afternoons.

What the report says

"While mean maximum temperatures are projected to increase by approximately 1.5°C, minimum temperatures during winter are set to depart by +2.1°C."

Communities likely to be affected

. Koli fishing communities
. Daily wage workers
. Street vendors
. Construction workers
. Residents in densely built neighbourhoods

What is relative humidity?

Relative humidity (RH) measures the amount of moisture present in the air.

Why it matters

Higher humidity makes it harder for sweat to evaporate from the body.

As a result:

. Heat feels more intense
. Risk of heat stress rises
. Outdoor work becomes more difficult
. Recovery from hot weather becomes slower