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Peak water flows in parts of India's largest river basin have been falling by more than one-sixth every decade, according to a published in npj Natural Hazards that highlights a similar trend across the country, impacting irrigation, domestic water, and hydropower in the world's most populous nation.

In the western and central Ganges River basin, peak outflows have declined by 17% per decade, the study showed, which the researchers blamed on falling rainfall and drier soil.

"Our study provides updated insights into how flood behavior is changing across India—both in terms of intensity and timing," said Sai Kiran Kuntla at the Indian Institute of Technology in Delhi, one of the study's authors.

"Such findings help bridge the gap between scientific knowledge and actionable planning, particularly as climate change alters flood risks."

The study analyzed river discharge data from 173 gauging stations across major Indian river basins from 1970 to 2010. It found that about 74% of the stations saw a significant decrease in peak flows. Researchers also noted shifts in the timing of these peaks across all basins.

Peak flow is a measure of water being carried by a river at its fullest. Understanding trends in peak flows can help estimate the flood risks and water availability in the region.

Urbanization

The magnitude and timing of peak river flows are shaped by a combination of natural and human-made factors. Climate change can alter rainfall patterns and soil moisture, while seismic activity like earthquakes and landslides may reshape river courses. At the same time, human interventions—such as urbanization, deforestation and the construction of large and small dams—can significantly modify a river's flow.

"In many Indian basins, high-flow events, including moderate floods, are critical for replenishing reservoirs, especially during the monsoon season," said Sharad Jain, a professor in the civil engineering department at the Indian Institute of Technology in Roorkee.

"These inflows are essential for meeting irrigation, domestic water supply, and hydropower needs."

"A decline in … peak flows could therefore have implications, as it may reduce the volume of water captured during peak flow periods, especially in basins highly dependent on monsoonal runoff," added Jain, who participated in the study.

In the Narmada basin, in central India, the decline is linked to dam construction during the same period. Meanwhile, in the drought-prone Deccan plateau in the southern part of the country, monsoon season peak flows dropped by eight percent per decade and pre-monsoon peaks fell by a striking 31% per decade.

"Peak outflows are a function of rainfall and soil moisture prior to rain," explained Ashish Sharma, a professor of civil and environmental engineering at the University of New South Wales, Australia, who didn't participate in the study.

"With temperatures on the rise, soil moisture is decreasing because of higher evaporation, and dry soil absorbs more water."

Studies have shown a clear shift in the monsoon rainfall patterns in India, where several regions are currently witnessing flash floods.

"Instead of steady, moderate rainfall across the season, we now see longer dry spells broken by short, intense downpours," said M K Roxy, climate scientist at the Indian Institute of Tropical Meteorology, Pune, who did not participate in the study.

'With unchecked urbanization, even a short spell of rain turns into a flood'

The study also found that the timing of peak flows has shifted. In many basins, earlier rainfall is leading to earlier flood peaks. Such changes can have major consequences for reservoir operations, irrigation planning and early warning systems.

"Our results signal a hydrologic regime that is becoming more erratic," said Manabendra Saharia, an associate professor of civil engineering at the Indian Institute of Technology in Delhi, and co-author of the study.

"Translating these insights into updated reservoir rules, urban drainage designs, and drought-relief plans is now urgent if we want India's water infrastructure to stay one step ahead of a changing climate."