When it rains in Mumbai, it actually pours

  • Mumbai is witnessing its second extreme rainfall event this monsoon
  • IMD says extreme rain events are rising globally. India is seeing fewer rainy days, but more extreme rainfall events

Mumbai came to a standstill yet again on Wednesday, bearing the brunt of a second extreme rain event this monsoon season. Mint takes a look at what is so unique about the heavy monsoon showers this year, and why India’s financial capital faces a deluge every time it rains.

What is happening in Mumbai right now?

Mumbai is witnessing its second extreme rainfall event this monsoon. The first was on 1 July when the city saw 375mm of rain in just 24 hours, the heaviest downpour. According to the India Meteorological Department (IMD), it was caused by a low pressure system which formed over the Bay of Bengal and moved aggressively towards the west coast. This was strengthened by a trough on the west coast, which added to the precipitation. The latest extreme rain event was on 3-4 September. Santa Cruz meteorological station recorded over 100mm rainfall each for the last three days, which went up to 242mm on Wednesday.

What is causing heavy rainfall in Mumbai?

Most of the low pressure systems forming over the Bay of Bengal have been moving west towards Mumbai, east Rajasthan and Gujarat after covering Odisha and Madhya Pradesh. This, according to the central meteorological department, is not a trend, but a part of the monsoon’s inter-annual variations. As a result, the country’s west coast has received excess rains. Additional systems forming around the same time have added to the woes. The 4 September rains, for instance, were caused by a low pressure system, a cyclonic circulation over Gujarat and an active trough along the west coast.

(Paras Jain/Mint)

Is climate change the reason for the deluge?

IMD says extreme rain events are rising globally. India is seeing fewer rainy days, but more extreme rainfall events. Climate change is a factor, but each monsoon has inter-annual variations.

Why has the city’s urban planning failed?

Mumbai is prone to flooding since large parts of it were low-lying marshlands. However, excessive development has led to reckless concretization, destroying the naturally percolating surfaces, and wetlands and mudflats, which could have slowed down the flow of storm water. So, during excess rains, rainwater adds to the run-off to the low-lying areas, like railway tracks, instead of percolating into the soil. The concern is that despite its high vulnerability, the city has not prepared a plan to tackle the emerging challenges.

How did the Mithi and high tide cause floods?

The situation worsened when heavy rains led to overflowing of the Mithi and water from the flooded river was pushed back by the high tide, submerging rail tracks at Matunga and Wadala, bringing the train and road traffic to a grinding halt. The incessant rainfall in the mountainous terrain of Western Ghats in Maharashtra also led to a sudden rise in water levels in west-flowing rivers. When there is a high tide in the seas during monsoon, it is also difficult for the flood waters to get to the seas.