Mumbai: Maximum City gets India’s ‘maximum’ weather radar cover

Every monsoon season, Mumbai suffers from severe waterlogging and urban flooding, crippling the road and rail traffic and throwing normal life out of gear. Mumbai falls under a heavy rainfall category. The city receives annual rainfall of 2,123 mm, of which 2,040 mm is recorded during the June-September period. Thane’s annual rainfall is 2,435 mm.

The new short-range polarimetric radars are best suited for dense and urban localities. Though similar short-range radar networks have been installed and tasted success in Japan, China and the US. Now, they are being experimentally attempted for Indian cities, where urban flooding following heavy rainfall has become an annual event.

Each with a range of 60 km, the four X-band radars will cover the entire Mumbai Metropolitan Region (MMR), spanning Vile Parle, Panvel, Vasai-Virar and Kalyan-Dombivali in addition to the area limits under the Brihanmumbai Municipal Corporation.

“For the first time in India, we are introducing the concept of a short-range polarimetric radar network set-up in Mumbai. The observations from each individual radar will be combined into a single mosaic, which will monitor the weather systems across the MMR. This unified mosaic will enable real-time tracking of rainfall activity, providing a comprehensive view of the weather patterns affecting the region. Since there are four radars, chances of any rain-bearing weather system getting missed are slim,” G Pandithurai, Senior Scientist and Project Director, Indian Institute of Tropical Meteorology (IITM), Pune, told The Indian Express.

IITM and the IMD are jointly operationalising the radar observations. Data from all the radars will be provided to the National Centre for Coastal Research in Chennai, which has been producing flood warning forecasts for Mumbai in recent years.

Of the total operational 39 S-band, C-band and X-band radars across the country, most have been installed along the east and west coasts and are both efficient and useful for tracking large-scale systems like low pressures and cyclones. An S-band radar has a range of 400 km, C-band between 150 and 200 km and an X-band offers up to 100 km. The short-range radars cover smaller geographical areas and are apt for mega cities, like Mumbai, where skyscrapers often obstruct the field of view of radars.

“Four radars have been strategically positioned to ensure that, even if one radar’s observations are blocked by tall buildings or other obstructions in a particular sector, the remaining radars will still have comprehensive coverage. The infrastructure requirements for the installation of short-range radars are less than a regular radar, making them easier to deploy in densely populated urban areas,” said Subrata Kumar Das, another IITM scientist involved in the project.

The IMD issues location-specific nowcast warnings ahead of a significant weather event, like thunderstorm, heavy rainfall, with a lead time of up to three hours. Such precipitation-centric nowcasts are particularly crucial for the local administration and decision makers.

“Forecasters will obtain high-resolution rainfall maps in real-time once these new radars get commissioned. While the existing two operational radars perform scanning once every 10 minutes, the four new short-range radars will scan at an interval of five minutes, ensuring no weather system goes undetected,” said Sunil Kamble, Head, Regional Meteorological Centre, IMD, Mumbai.

The biggest advantages of having a short-range radar network will be the significant improvement to the IMD’s nowcasts, said K S Hosalikar, Head, Climate Research and Services, IMD, Pune. The project was in its design phase while he headed the IMD office in Mumbai.

In order to optimise the network, these radars will operate with adaptive scanning techniques. This allows targeted and site-specific scanning.

“For instance, if rainfall is observed to be concentrated over a particular locality, all the four radars could be tuned to scan that location. In this way, we will be able to obtain more information and reduce the uncertainties in short-duration weather events, like thunderstorms,” Pandithurai explained.

Setting up such a state-of-the-art radar network in Mumbai will accelerate the observational capabilities of weather in urban areas.

Anjali Marar is a Science Communicator at Raman Research Institute.