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Most regions in the Indo-Gangetic Basin rely on monsoon rains for over 85% of their annual rainfall, and changing patterns under climate change are disrupting the streamflow.
As global temperatures rise, scientists are still debating whether the southwest monsoon is weakening or strengthening in response to climate change, especially over the Ganga river basin. (Image: Vimal Mishra)
The Ganga River Basin, lifeline of over 600 million people, experienced its most severe drying trend from 1991 to 2020 – the worst in the past 1,000 years, according to a new research, which examined 1,300 years of streamflow data and the increasing drought frequency amid an erratic monsoon.
The study was led by researchers from IIT Gandhinagar who reconstructed the streamflow history from 700 to 2012 CE using the Monsoon Asia Drought Atlas, as well as ancient climate records and computer models. The analysis published in peer-reviewed journal PNAS revealed that one of the country’s largest river basin faced frequent and prolonged droughts in recent decades, especially from 1991 to 2020, when it was the most extreme.
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“Streamflow has fallen significantly since the 1990s because of more frequent and longer drought. The decline in flow during this period was 76 per cent worse than the 16th century drought, the most similar event in the past. This drying is also unusually severe to be caused by natural variability alone, and seems to be driven largely by multiple factors, including monsoon and human activities, which require further study,” said co-author Professor Vimal Mishra from IIT Gandhinagar.
The changing dynamics in the largest river basin has implications for water and food security in the region, as well as Nepal and Bangladesh where the river flows. For instance, during 2015-17, historically-low water levels across the middle and lower reaches of the Ganga river severely disrupted drinking water supply, power generation, irrigation, and navigation affecting over 120 million people.
ERRATIC MONSOON: RECURRING FLOODS AND DROUGHTS
Interestingly, the findings contradict recent climate models, which project increased streamflow with warming. As global temperatures rise, scientists are still debating whether the southwest monsoon is weakening or strengthening in response to climate change, especially over the Ganga river basin. Either ways, the ongoing shifts in the rainfall patterns will have a severe impact on the region’s water availability, they concur.
“Future projections are far more complex, and this only highlights the challenges of predicting future water supply in the region. Overall rainfall over the entire basin is influenced by many factors – irrigation, aerosols, that most climate models often overlook or underrepresented,” said Professor Mishra.
A 2024 IISER Bhopal study found that though short bursts of extreme rain have increased across major regions of the Ganga basin since 1960, intensifying flash flood hazards, overall rain volume across the basin has dropped, especially in the eastern Indo-Gangetic plains and southern basin regions (Chambal, Betwa, Tons, Sone), signaling increased drought frequencies. The Himalayan regions – upper Ganga, upper Yamuna, and upper Ghagra, on the other hand, have seen increasing rain intensity, volume and duration post 1960.
Another important study by IITM Pune in 2015 threw light on the decreasing land-sea thermal contrast, with rapid warming in the Indian Ocean and slower warming over the subcontinent. This could lead to significant weakening trend in summer rainfall over central-east and northern India (1901–2012), with weakened monsoon circulation, which reduced rainfall in key agricultural areas.
85% OF ANNUAL RAIN DURING MONSOON
The data revealed there have been more wet years than dry years during the last 1,300 years, but 1990 onwards, there were no extreme wet years in the Ganga river basin between 1991 and 2010, and only two extreme wet years between 2011 and 2020.
Overall, the basin witnessed an unusual drying that is likely caused by the weakening of summer monsoon precipitation in the region, combined with severe and prolonged droughts which has become more frequent in recent decades. But as uncertainties surround the southwest monsoon, which provides over 75 per cent rains over the Indo-Gangetic basin, experts agree that it is important to uncover the factors driving the drying of the Ganga River to manage the important water source amid a warming climate.
“Our study highlights the need to better understand how different factors like large climate patterns, and human activities, aerosol emissions, irrigation affect the summer monsoon. Improving climate models with this knowledge is crucial to making accurate forecasts and managing water resources to protect the Ganga basin’s water in a changing climate,” the team noted.
About the Author
Srishti Choudhary, Senior Assistant Editor at CNN-News18 specializes in science, environment, and climate change reporting. With over a decade of extensive field experience, she has brought incisive ground repo…Read More
Srishti Choudhary, Senior Assistant Editor at CNN-News18 specializes in science, environment, and climate change reporting. With over a decade of extensive field experience, she has brought incisive ground repo… Read More
September 23, 2025, 16:32 IST
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