Study finds drying of the Ganga in recent decades 'unprecedented' in past millennium

New Delhi, Sep 24 (PTI) Drying of the Ganga river basin seen in recent decades could be severe and unprecedented, threatening water and food security for millions, an analysis of trends spanning 1,300 years suggests.

Findings published in the journal Proceedings of the National Academy of Sciences show that "drying from 1991 to 2020 is unmatched in the past millennium".

Researchers from the Indian Institute of Technology Gandhinagar and the University of Arizona in the US have linked the drying of the Ganga to reduced rainfall during the southwest monsoon (June-September).

The team used data gathered via instruments, historical records and models of water flow during 1991-2020, and reconstructed water flow models for the past 1,300 years (700-1990 CE).

"The Ganga River basin, critical to over 600 million people, is experiencing a severe and unprecedented drying trend, threatening water and food security," the authors wrote.

Drying of the Ganga seen since the 1990s and driven by frequent, prolonged droughts "is 76 per cent more intense than the 16th century drought -- the closest historical analogue," the team found.

A significant decline in total yearly rainfall of 9.5 per cent during 1951-2020 was estimated, with a more pronounced decline of over 30 per cent seen in India's western region.

The authors added that even though climate change is expected to intensify rainfall, a rapid warming in the Indian Ocean and subdued warming across the subcontinent have resulted in a weaker monsoon over north India.

Further, a weaker recharge of groundwater due to reduced rainfall, coupled with an excess drawing of the fast-depleting resource for irrigation, can also worsen the drying of the Ganga, they said.

Previous studies have projected that water flowing in the river basin could increase under continued climate change, with contributions from increasing rainfall and glacier melt.

However, the researchers said their study indicates how projections regarding the availability of water in a warmer future can be complex.

More studies are urgently required to look at interactions between factors that influence rainfall in monsoons, including natural climate change over the long term and that caused by humans, they added.

Based on abnormal flows seen in the past three decades, the authors projected the second most severe drying of the Ganga to have occurred during 1501-1530 -- in line with findings indicating an increased dryness in north India during the early 16th century, they said.

The third driest event for the Ganga was projected to have occurred during the mid-14th century (1344-1373).

"Overall, the river drying during 1991-2020 is unprecedented and more severe than its nearest two historical analogues during the entire record of 1,300 years," the authors said. PTI KRS RT