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The Ganges River is in crisis. This lifeline for around 600 million people in India and neighboring countries is experiencing its worst drying period in 1,300 years. Using a combination of historical data, paleoclimate records and hydrological models, researchers from IIT Gandhinagar and the University of Arizona discovered that human activity is the main cause. They also found that the current drying is more severe than any recorded drought in the river's history.

In their study, in the Proceedings of the National Academy of Sciences, researchers first reconstructed the river's flow for the last 1,300 years (700 to 2012 C.E.) by analyzing tree rings from the Monsoon Asia Drought Atlas (MADA) dataset. Then they used powerful computer programs to combine this tree-ring data with modern records to create a timeline of the river's flow. To ensure its accuracy, they double-checked it against documented historical droughts and famines.

The scientists found that the recent drying of the Ganges River from 1991 to 2020 is 76% worse than the previous worst recorded drought, which occurred during the 16th century. Not only is the river drier overall, but droughts are now more frequent and last longer. The main reason, according to the researchers, is human activity. While some natural climate patterns are at play, the primary driver is the weakening of the summer monsoon.

This weakening is linked to human-driven factors such as the warming of the Indian Ocean and air pollution from anthropogenic aerosols. These are liquid droplets and fine solid particles that come from factories, vehicles and power plants, among other sources and can suppress rainfall. The scientists also found that most climate models failed to spot the severe drying trend.

"The recent drying is well beyond the realm of last millennium climate variability, and most global climate models fail to capture it," the authors wrote in their paper. "Our findings underscore the urgent need to examine the interactions among the factors that control summer monsoon precipitation, including large-scale climate variability and anthropogenic forcings."

Avoiding a drier future

The researchers suggest two main courses of action. Given the mismatch between climate models and what they actually found, they are calling for better modeling to account for the regional impacts of human activity.

And because the Ganges is a vital source of water for drinking, agricultural production, industrial use and wildlife, the team also recommends implementing new adaptive water management strategies to mitigate potential water scarcity.

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