Cauvery basin at risk of repeated flooding

Cauvery basin at risk of repeated flooding

Visitors stand near the Wellesley Bridge over flooded Cauvery river, in Mandya, Sunday, Aug 11, 2019. PTI

As India stares at a heightened flood risk due to warming climate, the Cauvery basin in the south stands among the most vulnerable in the country.

Among the three major southern river basins, Cauvery carries more risk when compared to Godavari and Krishna, according to a new study on future flood risk. For the country as a whole, the Brahmaputra basin is the most vulnerable. 

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The chances of flooding due to extreme rainfall increase with a rise in greenhouse gas emission. The more the emission, the higher the flood risk.

Carried out by researchers at the Indian Institute of Technology, Gandhinagar, the new study suggests that the number of floods due to extremely heavy rainfall is projected to increase more rapidly.

Majority of the river basins would experience more cases of extreme rainfall continuing for 3-5 days, triggering flood. The number of such cases would be 30-40 more in the coming decades compared to what used to be the average between 1966 and 2005. In comparison, the risk of flooding due to a single-day heavy downpour would be less.

In a high-emission scenario, the Cauvery basin is expected to witness around 18 such flooding incidents between 2020 and 2059 due to multiple day continuous heavy rainfall. Godavari and Krishna, on the other hand, would encounter a dozen such events.

Between 2060 and 2099, the numbers would increase for all the three basins. While Cauvery is likely to witness nearly 28 occurrences, the corresponding numbers for Godavari and Krishna would be around 20.

Among the 18 basins, the highest increase in three-day extreme rainfall event would be in the Brahmaputra basin (up to 20 and 34 events for low and high emission scenario respectively).

On the other hand, the least projected increase in the frequency of extreme precipitation is likely in the Indus basin. The Ganga basin, one of the most populous and the largest basin in India, would be somewhere in between.

“The flood risks are two times more with higher emission, which demonstrates how crucial climate change mitigation is. The global community must act to reduce the emission that would cut flood risks by half,” Vimal Mishra, IIT Gandhinagar scientist and principal investigator of the study, told DH.

The researchers used weather data from the India Meteorological Department and sophisticated modelling tools for the study.

They also simulated the flood risk due to a single day’s extreme heavy rainfall, but concluded that multi-day flood events were projected to increase with a faster rate in the future than the single-day events, which could have strong implications for agriculture and infrastructure. The study has recently been published in the journal Weather and Climate Extremes.

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