Narmada and Mahanadi most prone to widespread flooding: study

Widespread floods experienced in the Indian subcontinent’s seven major river basins — Ganga, Brahmaputra, Godavari, Krishna, Mahanadi, Narmada and Cauvery — were examined between 1959 and 2020.

With 40 flooding events recorded during the six decades studied, the researchers found that the westward-flowing Narmada and the eastward-flowing Mahanadi rivers were the most prone to frequent flooding among all the river basins in India.

Enlisting some of the common reasons for widespread flooding, researcher and paper’s co-author Nanditha J S, said, “The uniform distribution of rainfall across the river basins, wet soil moisture conditions, high subsurface flow contribution before extreme rainfall events, and the relative nature of extreme rainfall events – all of these contribute towards widespread flooding.”

By and large, the core monsoon region in Central India showed the least variability in the distribution of total rainy days during the June to September summer monsoon months, the researchers shared.

The study, led by Vimal Mishra from the Civil Engineering and Earth Sciences, also noted that the availability of wet and moist soil in the river basins contributed to a higher water flow resulting in a flood-like situation.

Further, the study, published in the journal of the American Meteorological Society, calculated the river-wise flooding probabilities that ranged from Godavari (42 per cent), Krishna (38 per cent), Ganga (21 per cent) to Cauvery (19 per cent).

Almost every year, the mighty trans-country Brahmaputra breaches its river banks causing widespread flooding, especially in Assam and neighbourhood areas, leading to loss of lives and property.

However, the IIT-Gandhinagar researchers argued in their paper that the Brahmaputra reported less than 15 flood events during the said period.

“There is a relatively high variability in the spatial distribution of monsoon precipitation in the Brahmaputra basin. The upstream regions of the basin received less precipitation in comparison to the downstream reaches during the monsoon season. This, even as it rains more than 50 per cent of the time during the monsoon season across the river basin,” said Mishra, a Shanti Swarup Bhatnagar awardee.

Besides, the extreme flows in a few sub-basins were found to result in widespread flooding along the Brahmaputra, the researchers said.