Indian scientists prepare first urban flood forecasting

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Four years after the devastating Chennai flood that killed more than 500 persons, Indian scientists are ready with an urban flood forecasting model to ensure that lives are not lost in the southern metropolis if such a flood returns in future.

The model can be tailored for preparedness and timely response against an incoming flood event in the cities.

With financial support from the Office of the Principal Scientific Advisor to the central government, an Indian Institute of technology, Bombay team took the lead in developing India's first urban flood forecasting model, which is fully automated and has multiple components.

“We are now working on a plan to expand the flood forecasting model to other cities,” K Vijayraghavan, the Principal Scientific Advisor told DH.

In December 2015, Chennai and its surrounding areas were struck torrential rainfall triggering a deluge that not only killed people but also affected more than 40 lakh individuals and caused economic damages worth around $ 3 billion.

The forecasting system has six components — some running in parallel and a few dependent on each other. They include computational models that can give alerts on regional weather and tide surges and sensors that measures water levels in the rivers.

Other inputs come from tidal and ocean depth data obtained from Adyar, Cooum and Kosasthalaiyar river mouths in Chennai, water levels in these rivers, reservoir levels of Chembarambakkam and Poondi reservoirs; automated weather stations that capture weather data, historical rainfall records besides the current land use, topography and drainage data.

In addition, hydrological models, which consider reservoirs and river flows, are also included in the system, along with flood models that calculate which areas would be inundated.

The outcome is inundation maps with flood depths that are 80% accurate within one metre as compared to the real flooded regions. The remaining 20% are areas in north Chennai where two rivers drain into a major drainage canal. Better measurements of the cross-sections of the rivers would improve the forecasting accuracy in that area too.

“The entire expert system has now been transferred to the National Centre for Coastal Research, Chennai for day-to-day operations. From next year, the model is to be run by the Chennai municipal corporation and the state disaster response agency,” said Subimal Ghosh, the IIT Bombay professor who led the effort involving 30 researchers from 8 institutes.

“The model is to be updated in every 5 years as the land use and land use cover change,” said Ghosh, who won the prestigious Bhatnagar award in 2019. This is important as cities rapidly lose their water bodies and unplanned urban growth clog the archaic drainage system.

“The forecasting model, however, is not a magic solution for everything. There is no solution fits all. People on the ground have to work to improve the drainage,” commented Vijayraghavan.

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