Mumbai to get India’s second megacity flood warning system on Friday

The Brihanmumbai Municipal Corporation may get the country’s second urban flood warning system this Friday, for evaluation in Mumbai.

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The system was jointly conceived by scientists from the Indian Institute of Tropical Meteorology (IITM), Pune, India Meteorological Department (IMD), and National Centre for Coastal Research (NCCR), Chennai; all under MoES along with BMC. It will provide early warnings for heavy rain in flood prone areas in Mumbai and enable the civic body to issue alerts for citizens who can then avoid such zones. It will also provide rainfall information, tide levels, storm surge, and issue alerts for affected low-lying areas, which should be avoided during natural disasters such as cyclones and extremely heavy rain events.

The ministry of earth sciences (MoES) said the flood warning system would be made available to BMC on Friday. “This is will be the second such warning system for any city in India after Chennai and an important decision-making support system during flood incidents,” said M Rajeevan, secretary, MoES. “It will not be made public but only for evaluation, testing and utilisation by BMC this monsoon, and made available to citizens from next year.”

Rajeevan added this complex system would also calculate and provide information on increase in water levels across major rivers in the city, location-wise problem areas across all 24 wards, and waterlogging at slum pockets.

“Over the past two years researchers have been studying updated information of Mumbai’s drainage system, high-resolution digital elevation maps for all wards, population at each ward, observations of low-lying areas etc based on updated data provided by BMC. Combined with this, information from 160 rain gauges [instruments to measure rainfall] will provide near real time weather information,” said Rajeevan.

Dr. MV Ramana Murthy, director, NCCR, said using rainfall and inundation models through flooding maps, the system will be able to provide vulnerability and risk assessment well in advance. “While the basic principle of the system is similar to that shared with the Chennai municipal corporation, the methodology used to detect specific details will be different for Mumbai since parameters are different,” he said.

Scientists said the warning system was crucial considering the dense urban settlements of the city. “We have witnessed a three-fold increase in extreme weather events over parts of central India and west coast, including Mumbai, over a 66-year-period (1950-2015). Considering the population density and infrastructure at risk due to extreme weather, Mumbai has to be the first target,” said Dr. Roxy Mathew Koll, senior scientist, IITM Pune.

The India Meteorological Department (IMD) will provide three- to six-hour Nowcast (immediate weather updates) as well as 72-hour early warning forecast as it has been doing. “This will be a robust system to monitor real-time weather event occurrences and timely warnings where the impact of storm surge and rising tides will also be accounted for while assessing risks,” said Mrutyunjay Mohapatra, director-general, IMD.

The first early warning system for Chennai was developed by professors Subimal Ghosh and Subhankar Karmakar of Indian Institute of Technology Bombay (IIT-B), following the 2015 floods that led to over 150 deaths. “Every monsoon there are at least three extreme weather events (with almost 200mm rain or more) in Mumbai leading to extreme difficulty for commuters. With this, citizens will have prior information on flooding hotspots, and have proper planning for public and private transportation systems. It is a complex system with multiple components. I am happy that the Chennai model will be replicated in Mumbai,” said Ghosh.

Independent experts said the system’s first public test after operationalisation was likely to be in mid-June when active monsoon conditions are expected in the city. “Such early flood warning systems will be useful in Mumbai given the city’s large expanse and other factors such as population density, proximity to the sea and low elevation of areas. However, a big challenge will be in accurately issuing flood alerts (especially the flood duration) during bursts of intense rain showers that inundate the city,” said Akshay Deoras, meteorologist and PhD researcher at the department of meteorology, University of Reading. “Hourly weather forecasting in Mumbai is challenging during active monsoon conditions and weather models still have lots of limitations.”

INSTALLATION OF 4 NEW DOPPLER RADARS PUSHED TO NEXT YEAR

Owing to delays in shipments from the United States of America (USA) due to the Covid-19 pandemic, four X-band Doppler radars will be installed in 2021. Originally, two radars were to be set up in Mumbai this year along with one each in Thane and Navi Mumbai. The radar provides long-range weather surveillance, detection and forecast for rainfall, cloud formation, thunderstorms and other weather conditions such as tropical storms with a range of up to 50-60km. “Orders were placed for the equipment, and we were informed they would be shipped by this time from USA. However, as a result of the Covid-19 pandemic, the entire acquisition process has been delayed by a year,” said M Rajeevan, secretary, MoES. While one major radar located at the Regional Meteorological Centre in Colaba can carry out weather surveillance at distance of 300 km radius from its location, a second large radar planned in Goregaon is expected within a couple of months, said Rajeevan.