Mumbai’s mega money, mini drains: Why maximum city still sinks every monsoon

Mumbai, India's financial capital which contributes nearly 40% to Maharashtra's GDP, sinks every year with onset of monsoon, with life in a city which never sleeps coming to a standstill. Heavy rains hit Mumbai as the annual monsoon rains arrived some two weeks earlier than usual, according to weather forecasters. With heavy rains and flooding, Mumbai has broken its 107-year-record of receiving highest rains in the month of May.

As per a BMC report, Mumbai has been witnessing a steady increase in extreme rainfall events. Over 35% of Mumbai’s population lives within a 250m radius buffer of flooding hotspots. Nearly 65% of its population are exposed to the risk of flooding.

Maharashtra Deputy Chief Minister Eknath Shinde on Monday attributed early arrival of the southwest monsoon and heavy rainfall in a short span for the inundation of low-lying areas in Mumbai, which disrupted road and railway traffic. Addressing reporters, he said parts of the city received over 200 mm of rainfall in 12 hours.

Financial capital drenched
As per IMD data, the weather agency's Colaba observatory recorded 135.4 mm of rainfall in the 24 hours ending 8:30 am Monday, categorised as "very heavy rain" (115.6 mm–204.4 mm). In contrast, the Santacruz observatory in the suburbs recorded 33.5 mm.

"The Southwest Monsoon has advanced to Mumbai today, May, 26 2025, against the normal date of advancement, June 11," IMD said in a statement. "Thus, the monsoon has arrived in Mumbai 16 days earlier than usual. This marks the earliest monsoon advancement over Mumbai during the period 2001–2025."

Mumbai, the capital of the state of Maharashtra, a megapolis and the financial capital of India has been experiencing floods with increased periodicity and almost every monsoon, Mumbai struggles to cope with the chaos caused by the rains. The suburban trains which serve as the city's lifeline gets affected, low-lying areas get flooded, traffic jams and water logged streets add to the woes of the Mumbaikars.

What would be burden of heavy rains on Mumbai?
Mumbai among the list of coastal cities including New York City, Tokyo, Jakarta, Shanghai and Lagos, that are at serious risk to climate change. Under RCP 8.5, without adaptation, a study estimates expected damages in Mumbai due to sea level rise to go up to $50 billion by 2050, making it the second most-at-risk city globally.

Mumbai is at high risk to flooding – driven not only by climate change and heavy rainfall but also by socio-economic and political factors affecting its exposure and vulnerability unequally.

A recent paper published in Nature estimates that, under high emissions scenarios, global sea levels could rise by an average 1 to 2 meters by 2100. Combined with a severe downpour, a flood like the one below could hit Mumbai.

Settlement causes trouble for Mumbai
Settlements on unstable slopes face increased prospects of rainfall-induced landslides. As per the data recorded by the Disaster Management Department at BMC, there are 287 locations within Greater Mumbai that are landslide-prone out of which 209 locations fall within the extent of informal settlements characterized by unstable structures and societal vulnerabilities.

As per the India Meteorological Department (IMD) Mumbai and other areas along the Arabian Sea were subjected to 18 cyclone events between 2011 to 2021. This is due to a slow, but steady, increase in annual mean sea surface temperature of the Arabian Sea.

The western coastline of Mumbai doesn’t show a dramatic change over years, in the form of erosion or accretion, due to ‘tetra pods’ that absorb strong tidal impacts.

Stormwater drains' role in Mumbai floods
Mumbai's recurring flooding issues can be largely attributed to its existing storm water drainage system, which is a complex network of simple drains, rivers, creeks, and ponds. Some of these outfalls drain directly into the Arabian Sea, while others discharge into the Mahim, Mahul, or Thane creeks. In the western suburbs, certain outfalls release storm water straight into the sea, whereas the rest channel it into the Mithi River, which eventually flows into the Mahim Creek.