BENGALURU: With floods increasing in various parts of the country, researchers and hydrology experts say it is time to expand the horizon of flood studies from individual basins to regional scale analysis.
A study by IISc researchers showed that rivers are interconnected, and this is evident when flooding is reported in one river, other rivers also report flooding in the following days. In a report titled ‘Spatial Synchronization of River Floods Growing Beyond the Basin Boundaries in Peninsular India’, which was also published in Scientific Reports, the researchers noted that flood risk assessment studies should not be restricted to individual basins.
Shailza Sharma, postdoc from IISc Bangalore, Department of Civil Engineering, IISc, and co-author of the report, said that earlier there was limited data, and it was understood that flooding was only because of severe rainfall. But now, with sufficient data, it is also known that flooding is because of spatial dependence of rivers. Shailza, who is also a researcher at ICAR, CRIDA, Hyderabad, said spatial dependence of floods varies regionally and has been increasing, extending beyond individual river basin boundaries. An increase in flood connectedness has been found, which can be attributed to changes in the spatial dependencies of other flood drivers, apart from rainfall, soil moisture and anthropogenic factors.
Researchers noted that catchments that are not physically connected have shown flood co-occurrence over long distances. Researchers also identified five flood clusters. Cluster-1 included catchments of the Godavari middle sub-basin, Krishna basin except lower sub-basin and Pennar river basins. The catchments of Cluster-1 have the lowest daily mean precipitation and higher potential evapotranspiration.
Cluster-2 included catchments of lower Godavari, Indravati, lower Weinganga and lower Krishna sub-basins. The mean flood discharges are higher in Cluster-2 compared to other clusters, and catchment areas are also large. Cluster-3 included catchments of the Mahanadi basin, Subernarekha basin, Brahmani and Baitarni river basins, lower Narmada and catchments of Weinganga sub-basin. Cluster-4 comprised the catchments of Cauvery basin, west-flowing rivers between Tadri and Kanyakumari, and east-flowing rivers between Pennar and Kanyakumari. Cluster-5 comprises all catchments of the Narmada and Tapi basins, west flowing rivers between Tapi and Tadri, and a few catchments of the Weinganga and Wardha sub-basins.