Are recent frequent high floods in Mahanadi basin in eastern India due to increase in extreme rainfalls

Summary The Mahanadi river basin, a major river basin in eastern India, is expected to be the worst affected river basins in India in terms of the increase in intensity of floods due to climate change. The last decade has already seen five high floods occurring in the Mahanadi basin. Are these recent high floods an indication that Mahanadi floods are already getting worse? If so, is it due to an increase in extreme rainfalls over the basin? To answer these, we analyse the trends of peak discharge at the mouth of the delta at Naraj gauging site (the flow which is responsible for floods in the delta of Mahanadi basin) and peak releases from Hirakud dam in Mahanadi basin. Subsequently, grid based analysis of extreme rainfall is carried out for the entire Mahanadi basin to analyse the spatially varied extreme rainfall trends. Also, a region based (upper and middle regions of Mahanadi basin) analysis of extreme rainfall is carried out using daily mean areal rainfall. The trends of extreme rainfalls are analysed in relation to the trends of peak floods. The entire analysis pertains to post-Hirakud dam construction period. The analysis reveals that the recent incidences of high floods in Mahanadi basin is due to an increase in extreme rainfall in the middle reaches of the basin.

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