A TEAM of 30 scientists from eight institutions across the country led by IIT Bombay has developed a real-time and integrated urban system to predict floods in Chennai. This system can also be used in other cities and its framework is presently being used by Ministry of Earth Sciences to develop a similar forecasting system in Mumbai.
Pitched as the first-ever integrated expert system for an entire city in India to forecast floods, it has computational models that can forecast regional weather and surges in the tides and storm, apart from other things. This system includes all forecasts in a single framework weather, storm surge, tide, hydrology, hydraulic and urban inundation, said Professor Subimal Ghosh of department of civil engineering at IIT Bombay.
This expert system is a computer-based programme that makes decisions and predictions based on a set of data. It also has data from sensors that measures water levels in the rivers. The system is likely to come into operation from next year.
Before the 2015 Chennai floods, no framework for forecasting was available. There were models which spoke of a small region in the city but it didn t make sense because a municipal corporation would be interested in the entire city. Urban floods are not just about rainfall but also low-lying regions, flood-prone regions, high tide among others, Prof Ghosh told The Indian Express.
The study has been published in the journal Current Science and was funded by the Office of the Principal Scientific Adviser to the Government of India. The committee of experts was chaired by Dr Shailesh Nayak, former Secretary, Ministry of Earth Sciences (MoES).
The expert system designed by researchers has six components – some running in parallel and dependent on each other. Hydrological models, which consider reservoirs and river flows, are also included in the system along with flood models that calculate which areas will be inundated.
Other factors include historical rainfall data, current land use, topography and drainage data. The system produces visual maps of forecasted inundation. All these components are automated and need no manual intervention at any stage.
The complex calculations based on these parametres happen quickly in the expert system. Normally, National Centre for Medium-Range Weather Forecasting (NCMRWF)releases the forecasts at 3 pm, and within the next two hours, our expert system will release the first forecast for the next three days, Ghosh said. If there is a forecast of heavy floods, the real-time computing operation starts, and the forecast will be updated every six hours, he added.
The level of detail obtained can help rescue and alert operations. The expert system also has a databank to speed up the process of forecasting. It has 796 scenarios resulting from rainfall extremes with different severity of water flow and tides, and past rainfall.
Flood simulations for large cities can take a long time.
We have generated the extreme possible cases in a data bank, Ghosh added.
As soon as the input forecasts arrive, a search algorithm finds the closest scenario from the data bank and releases the first forecast. The researchers have validated their system with data from the December 2015 floods.
They found that their inundation map with flood depths was 80 per cent accurate within one metre as compared to the real flooded regions.