Outlook Explains | Mumbai's Record Rain During El Niño: Why Is Monsoon Breaking The Rules?

Mumbai has recorded an extraordinary spell of rainfall this July, even though India continues to experience the effects of El Niño—a climate pattern usually associated with delayed and weaker monsoons.

Between July 1 and July 7, the India Meteorological Department's (IMD) Colaba observatory recorded 791 mm of rainfall, exceeding its entire July average of 768.5 mm. Santacruz received 879 mm, nearly touching its monthly average of 919.9 mm in just one week.

While the monsoon arrived in Mumbai nearly two weeks later than usual, it turned exceptionally active by the end of June. Experts say there is no contradiction: El Niño may delay the monsoon, but once favourable weather systems develop, climate change is making rainfall more intense and erratic.

Why is Mumbai seeing record rain?

Mumbai's recent rainfall is the result of multiple weather systems becoming active simultaneously.

According to Dr Raghu Murtugudde, Emeritus Professor at the University of Maryland and former IIT Bombay professor who spoke to The Indian Express, moisture from both the Arabian Sea and the Bay of Bengal has been feeding the monsoon, while a low-pressure area over the Bay of Bengal further strengthened the system.

As this moisture reached the west coast, the Western Ghats forced the moisture-laden winds to rise, producing intense rainfall over Mumbai and coastal Maharashtra.

The latest spell also reflects a longer-term trend. Mumbai's average annual rainfall increased from 2,325.8 mm between 1981 and 2000 to 2,672.7 mm between 2001 and 2024—an increase of nearly 15 per cent.

Doesn't El Niño usually reduce rainfall?

Traditionally, yes. El Niño refers to unusually warm sea surface temperatures in the central and eastern Pacific Ocean, which often delay the southwest monsoon and reduce the number of rainy days over India.

This year, Mumbai's monsoon arrival was delayed by nearly two weeks, while Gujarat, Madhya Pradesh, Chhattisgarh and Maharashtra also saw a delayed onset.

However, the Prime Minister's Office, citing IMD officials, has stressed that an El Niño year does not necessarily result in below-normal rainfall. Rainfall across India improved significantly during the first week of July, reducing the national monsoon deficit to 12 per cent, while a weak-to-moderate El Niño is expected through July and August.

So why is Mumbai getting flooded?

Scientists say global warming is changing not just how much it rains, but how it rains.

A warmer atmosphere and rapidly warming oceans allow the air to hold more moisture. Instead of steady rainfall spread across several days, rain increasingly falls in short, high-intensity bursts that overwhelm drainage systems and trigger flash floods.

Dr K. J. Ramesh, former Director General of the IMD, said to The Indian Express that although El Niño years generally have fewer rainy days, "the character of the monsoon has changed permanently due to global warming," with rainfall now occurring in short-duration, high-intensity spells.

Is climate change making El Niño less predictable?

Experts say El Niño can no longer be viewed in isolation from climate change.

According to Dr Murtugudde, global warming over West Asia, changing Arabian Sea wind patterns and warming oceans are increasingly interacting with El Niño, making monsoon behaviour more complex than in the past.

As a result, while El Niño still influences when the monsoon arrives, climate change is increasingly determining the intensity of rainfall once weather systems become active.

Can heavy rain continue despite El Niño?

Meteorologists say delayed monsoon onset does not prevent episodes of intense rainfall later in the season. Once favourable atmospheric conditions develop, heavy rain can occur even during an El Niño year.

Although the current spell appears to be easing—with both Colaba and Santacruz recording below three-digit rainfall totals for the first time in five days—the IMD says monsoon conditions remain active, even as its latest forecast points to lighter rainfall over Mumbai and neighbouring Thane in the coming week.

How local weather systems override El Niño

While El Niño shapes large-scale climate patterns, local weather systems ultimately determine where and how much rain falls.

This week, simultaneous moisture inflow from the Arabian Sea and Bay of Bengal, a developing low-pressure system over the Bay, and the lifting effect of the Western Ghats combined to produce exceptionally heavy rainfall over Mumbai.

For scientists, the latest spell reinforces a broader shift: understanding India's monsoon now requires looking beyond El Niño alone and recognising how global warming and regional weather systems increasingly work together to shape extreme rainfall.