Didn’t see it coming, admits IMD after ‘extremely heavy rains’ pound Mumbai
The India Meteorological Department (IMD) failed to issue the correct forecast on Sunday or on Monday morning for extremely heavy downpour from late Monday night to early Tuesday morning that left the city a shambles.
Mumbai recorded 375.2mm (exceptionally heavy category) rain over 24 hours, with 241mm recorded over a nine-hour period. This was the second highest rainfall for the city since 1975 after the 2005 deluge that killed over 1,000 people.
Till 8pm on Monday, the forecast said ‘intermittent rain with heavy to very heavy falls in few areas’. After showers intensified around 11pm, the forecast was changed as late as 2am on Tuesday on IMD’s website (after exceptionally heavy rain) that ‘isolated areas could receive extremely heavy rain’. Subsequently, the Maharashtra government and Brihanmumbai Municipal Corporation (BMC) issued orders for schools, colleges and even offices to remain shut on Tuesday.
““On Monday, we had issued rainfall warning of heavy to very heavy rain in some areas, but it was not anticipated that extremely heavy rain would occur. The highly localised weather system developed very fast and we could not include such forecast in our 24-hour warnings,” said KS Hosalikar, deputy director general, western region, IMD. “This happened due to a cloud patch over the Mumbai suburbs with maximum rain intensity over Santacruz that led to continuous extremely heavy showers for six hours straight. However, warnings were modified and authorities were notified by 12.30am Tuesday morning, and our website was updated by 2am.”
Shubhangi Bhute, scientist, IMD Mumbai, said, “It was not realised that there would be continuous downpour in one go as when heavy to very heavy rain with isolated extremely heavy showers take place, there is break in downpour, but in this case that did not happen. The matter was assessed by the department on Tuesday and necessary warnings issued.”
From 2am to 12.30pm Tuesday, IMD’s warning of ‘heavy to very rain in city and suburbs with isolated extremely heavy falls’ continued. However, between 8.30am and 12.30pm, the suburbs recorded 19.5mm rain, while south Mumbai recorded 43.6mm, both falling under IMD’s own classification of ‘moderate’ showers with isolated patches in the suburbs even witnessing pockets of sunshine. At 12.30pm, IMD revised its forecast by downgrading heavy rain warnings to ‘intermittent showers with isolated heavy rain in city and suburbs’. “Weather models showed that the east west wind shear zone (weather system) leading to very heavy rain with isolated extremely heavy downpour had weakened and Mumbai’s Doppler weather radar did not indicate any significant cloud development,” said Bhute.
Citizens said prior arrangements could have been made if warnings were issued earlier. “Even if a brief mention of extremely heavy downpour was made by IMD six hours in advance, it would have given the civic body as well as citizens some time to either vacate low lying areas or take remedial steps to ensure rainwater did not enter homes,” said Brijesh Chawla, resident of Andheri (East) who said his society till 10.30am.
Independent meteorologists said current weather forecasting models have limitations when it comes to identifying short lived high-impact rainfall events that occur over a smaller geographical area (such as the one over Mumbai suburbs between Monday night and Tuesday morning). “These events are driven by thunderstorms that get enhanced due to local weather factors. Thus, a forecast valid for 24 hours might fail to indicate such possibilities,” said Akshay Deoras, meteorologist and PhD researcher at the department of meteorology, University of Reading, UK. “This is when Doppler weather radars are useful as they can track these developments on a real-time mode allowing meteorologists to notify disaster management authorities.
Deoras added that there persists a massive lag in updating of Mumbai’s Doppler radar products on the website. “This lag is currently as much as one hour, which is long enough for any thunderstorm to form and cause destructions. In fact, this lag is equivalent to the one observed in the case of updating satellite images,” he said.
44% false rainfall alarms for Mumbai in 2017
HT had reported in March 2018 that the India Meteorological Department, Mumbai issued 32 rainfall warnings in 2017, of which 14 turned out to be incorrect, revealed a right-to-information (RTI) query from the weather bureau. This means 44% of the predictions of heavy, very heavy or extreme rainfall warnings issued by IMD were wrong. International weather agencies at major cities like London, Miami, New York, and Dubai etc. ensure accuracy rate of 80% to 85% throughout the year, said Akshay Deoras, meteorologist and PhD researcher at the department of meteorology, University of Reading, UK.