Flood forecasting system didn’t help
The city’s flood forecasting system was unable to assist the civic body during the exceptionally heavy rain on Wednesday, the Brihanmumbai Municipal Corporation (BMC) said.
Inaugurated on June 12, the integrated flood warning system for Mumbai (iFLOWS-Mumbai), the second for any urban city (after Chennai) in the country so far, was developed to provide possible extent of flooding in Mumbai three days prior to heavy rain events and warnings to areas susceptible to flooding across all 24 wards 12 hours in advance. The system was launched on a trial basis this monsoon and based on its success, it was to be made public next year.
“The system is not fully functional and not handed over to BMC yet. Although it is being used on an experimental basis, it did not provide any alerts to us about possible areas to be flooded 12 hours in advance. We were only aware about the extremely heavy rain event three days prior. No bulletin was issued either on Tuesday or Wednesday,” said BMC’s disaster management chief officer Mahesh Narvekar, adding Wednesday’s rainfall and unprecedented wind speed was the most severe weather event witnessed in south Mumbai over the past two decades.
When the July 2005 deluge struck Mumbai, Santacruz had recorded 944.2mm rain over 24 hours, but the Colaba weather station, 27km away, had recorded only 73mm. “There was no prior intimation of extremely high wind speed that caused the tree fall and infra damage,” said Narvekar.
Since its launch, IMD made public the flood warning bulletin on July 3, 14 and 15 that issued warnings for 656 spots across 24 wards in the city, dividing them into categories ranging from low probability (less than 1-ft depth), moderate (1-2ft depth), high (2-3ft depth) and very high (over 3-ft depth).
“These warnings for Wednesday could have helped direct our manpower to locations faster. However, there is a difference in issuing the forecast and the ground reality. In all, over 200 tree fall incidents were reported across south Mumbai, and major flooding was reported from 25 spots that took seven hours for the water to recede,” said Narvekar.
The system was jointly conceived by various departments of the Ministry of Earth Sciences (MoES) and BMC. “I was recently informed about some technical issues at our observatories due to the Covid-19 pandemic. At a couple of observatories, people were unable to go and repair them. However, we will cross-check what happened,” said M Rajeevan, secretary, MoES.
IMD director-general Mrutyunjay Mohapatra said, “Apart from an accurate forecast for all three days, wind warning for the port and fishermen identified maximum wind speed at 70-80kmph. The iFLOWS system is being studied on an experimental basis, and we will check if there were any technical problems.”
Additional municipal commissioner P Velarasu said the accuracy of actionable advanced warnings using the system need to be validated with ward units. “There needs to be a verification mechanism. On the day forecasts were issued, broad trends for three to six hours have been accurate, but exact detailing and fine-tuning are not available yet. IMD is giving an area-specific forecast, but we have spot-specific issues. We need to check how the ward-wise forecast can be narrowed down for specific areas,” he said.
A senior BMC official said that on Friday they are holding a meeting with the National Centre for Coastal Research (NCCR), one of the MoES bodies, for further deliberations about the project.