Mumbai rain updates: City to now monitor rainfall with high-resolution radar network

Dark clouds gather over Nariman Point on Thursday evening. Pic/Anurag Ahire

The IMD will now have access to high-resolution, real-time rainfall maps from a network of six radars, including two of their own. This advancement is made possible by the Indian Institute of Tropical Meteorology (IITM) in Pune, which has established India's first Urban Radar Network in Mumbai by deploying four closely spaced X-band polarimetric radars (short-range polarimetric radars). This comes amid criticism faced by IMD over unfunctional radars from time to time. According to Sunil Kamble, scientist and head of IMD's Regional Meteorological Centre in Mumbai, these four new X-band radars have already been installed and are currently undergoing testing and technical assessments.

When asked about allegations regarding non-functional radars during extreme weather events, Kamble said, "We have maintained full transparency - there's nothing to hide, nor do we try to. Sometimes, due to technical issues, we may not receive data from the radars, but this does not mean we are unable to issue timely forecasts. Our forecasts are not based solely on radar data, they are the result of multiple exercises, observations, procedures, calculations, and recalculations performed daily."

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The S-band radar, installed in 2010 at the Regional Meteorological Centre in Colaba, South Mumbai, was non-functional a day before Severe Cyclonic Storm Nisarga passed by Mumbai's coast on June 2, 2020. Similarly, in June and July 2019, when the city experienced extremely heavy rainfall, the Doppler radar was inoperative due to technical difficulties. It also failed to provide timely and accurate data during Cyclone Ockhi on December 4, 2017. The C-band radar, covering a 450 km area around Mumbai, was virtually inaugurated in January 2022 during the 147th IMD Foundation Day celebration. This radar, designed and developed by ISRO's Telemetry Tracking and Command Network (ISTRAC), was manufactured by Data Patterns, Chennai.

New radar operations

Discussing the upcoming radar expansions, Kamble said, "Mumbai will soon have six weather radars monitoring the region, making it the most extensively covered city in India for weather surveillance. Two of the currently operational radars, an S-band radar in Colaba and a C-band radar in Veravali, are owned and maintained by IMD's Regional Meteorological Centre in Mumbai. Alongside, hundreds of rain gauges measure real-time rainfall at regular intervals. The IITM in Pune has recently deployed four closely spaced X-band polarimetric radars across Mumbai, which are best suited for monitoring dense urban areas."

The four newly installed X-band radars, each with a range of 60 kilometres, will provide coverage across the entire Mumbai Metropolitan Region (MMR). This includes areas such as Vile Parle, Panvel, Vasai-Virar, and Kalyan-Dombivli, along with areas under the jurisdiction of the BMC. IMD has been long planning to get these four X-Band radars, which have a surveillance radius of 60 to 100 km. In 2022, the weather bureau announced the plan to strategically set up these in different locations in the city to have spatial coverage of hyperlocal weather changes. The X band radars can better detect convective clouds and thunderclouds, which caused heavy rain in July 2005 leading to the deluge.

Radar operations are being jointly handled by IITM and IMD, with data from the radars being shared with the National Centre for Coastal Research (NCCR) in Chennai. The NCCR has been responsible for issuing flood warnings for Mumbai in recent years. The IMD, on the other hand, provides localised "nowcast" alerts, giving up to three hours of advance warning for major weather events like thunderstorms, hailstorms, and heavy rainfall. These timely warnings are crucial for local governments and decision-makers to take appropriate action. "Once these new radars are operational, forecasters will have real-time access to detailed rainfall maps. Unlike the current two radars, which perform a scan every 10 minutes, the new short-range radars will scan the area every five minutes, ensuring that no weather system is missed," Kamble explained.