Mumbai rains overwhelm drains: BMC eyes 120mm/hour upgrade; 80 new flooding spots found

MUMBAI: Brihanmumbai Municipal Corporation (BMC) have begun planning to overhaul parts of the city’s drainage network after intense one-hour downpours exposed the limits of its stormwater infrastructure.BMC is considering increasing the drainage capacity in vulnerable low-lying areas to handle up to 120mm of rainfall per hour, more than double the current capacity of 55mm.The move follows an alarming rain event on May 26, when the Nariman Point weather station recorded 104mm of rain in just one hour. Several other parts of south Mumbai saw similar deluges — 86mm at the A Ward Office, 80mm at the Municipal Head Office in Fort, 67mm at Grant Road Eye Hospital, 63mm at Malabar Hill, and 61mm at Nana Chowk’s D Ward — highlighting the urgent need for an infrastructure upgrade.Mumbai’s core stormwater drains date back to the British era and were originally designed to carry 25mm of rainwater per hour.

After the devastating floods of July 26, 2005, the Chitale Committee recommended upgrading the city’s system to accommodate 50mm/hour, and a phased widening project raised the figure slightly to 55mm/hour in the years that followed.But civic officials now say that’s no longer enough.“Drain width will have to be increased in vulnerable locations at least which are likely to impact a major population,” a senior BMC official said, citing rainfall pattern data from the past six years.

Between 2019 and 2024, Mumbai recorded an average high-intensity rainfall of 182mm, up sharply from 131mm during 2014–2018. In 2024 alone, the city recorded over 100mm of rain on 21 separate occasions, the official added.BMC engineers are currently identifying critical stretches of the city’s stormwater system that require urgent widening to reduce flooding risk during peak monsoon spells.The recent intense showers have also revealed new vulnerabilities: of the 120 waterlogging spots observed during May’s rains, officials say nearly 80 were new, appearing for the first time. The rainfall during these events ranged from 77mm to 104mm — all within just one hour.The proposal to strengthen Mumbai’s drainage system is still under internal review, but officials have indicated that implementation may be fast-tracked ahead of the next major monsoon cycle.