Why Mumbai feels hotter than ever: Humidity, concrete and vanishing green cover

Illustration/Uday Mohite

Mumbai's summers are no longer just about rising temperatures. Increasing humidity, disappearing tree cover, endless concretisation and rapid vertical growth are changing how heat is experienced across the city. Even on days when temperatures appear "normal", many Mumbaikars feel exhausted, dehydrated and suffocated outdoors.

To understand why the city feels far hotter than what thermometers show, mid-day spoke to meteorologists, climate experts and researchers about humidity levels, El Nino, urban heat islands, air quality, shrinking green cover and Mumbai's changing skyline, and how all of these factors are intensifying heat stress across the Mumbai Metropolitan Region.

What has been the average humidity level in Mumbai over the past 10 years during the summer months of March to May?
Gufran Beig, an Indian meteorologist and scientist, said, "Relative humidity (RH) is a combination of temperature and wind speed. This changes from season to season." Winter months report lower RH, whereas summer months witness relatively higher humidity levels. Generally, the monsoon season records highest RH, going up to 90%. However, this year, several summer days have reported average humidity levels between 50% and 70% in Mumbai, with levels peaking between 89% and 92%, according to the IMD.

How many kilometres of roads have been concretised in Mumbai over the past 10 years?
Athreya Shetty, a weather expert, said, "No, the current heat in the MMR cannot be attributed to El Nino, as it is still developing. A full-fledged El Nino is only expected after July, so its impacts are likely to be felt towards the end of the year and in summer 2027.

The current heat is part of normal seasonal variations during Mumbai summers. When the seasonal anticyclone over the Arabian Sea periodically extends its influence, it causes northerly and easterly winds that delay the sea breeze and cause spikes in temperature between March and May."

However, Gufran Beig offered a different view. He said, "Yes, this particular El Nino is related to severe and extreme climatic conditions. Summers are likely to become hotter and more humid because of the El Nino effect. El Nino and La Nina are phenomena linked to the warming and cooling of the Pacific Ocean. Depending on their severity, temperatures across the globe are affected, leading to unusual weather patterns.

"This particular El Nino can be termed a severe El Nino, which leads to harsher summers and erratic monsoons. The IMD has already indicated possibility of a weak or below-normal monsoon this year. Severe El Nino conditions also lead to erratic humidity levels, which are usually on the higher side, as experienced this year."

How many "good AQI" (Air Quality Index) days has Mumbai recorded over the last five years?
Between January 2021 and March 2025, according to CPCB data assessed and tabulated by mid-day

Good: 145 days
Satisfactory: 649 days
Moderate: 637 days
Poor: 184 days
Very Poor: 3 days
Severe: 1 day

How much has Mumbai's urban tree cover decreased over last 10 years?
Between 2015 and 2026, Mumbai lost more than 2000 hectares of urban tree cover, according to the BMC's Mumbai Climate Action Plan.

2000ha

1745 km
Effectively, around 1745 km out of Mumbai's total 2050 km road network has now been concreted.

2050 km
Mumbai has a total road network of approximately 2050 km. Before 2023, around 1224 km of roads had already been concretised.

Rs 17,000 crore
In 2023, the BMC launched a Rs 17,000 crore project to concrete an additional 700 km of roads. Of this, 521 km have already been completed.