Nearly a billion people to be affected by water scarcity by 2100, warns analysis

Nearly a billion people across the world are expected to face water scarcity through the effects of declining runoff from the world’s major rivers by 2100, a latest analysis done by researchers from the US-based Northeastern University has underlined.

Already, widespread decline in runoff is evident in 67 per cent of the world’s largest river basins, particularly in tropical regions of Africa and South Asia, where major population increases have been observed, the researchers note.

Countries with low GDP per capita and low Human Development Index (HDI) are being impacted by decreasing runoff with heavy population, and future projections also indicate that 40 per cent of the world’s largest river basins could experience decreasing runoff, they said, adding that the primary reasons behind the declining runoff in many major river basins are thought to be climate change and human activities.

Climate change has led to reduced rainfall in several regions, directly impacting water availability. Additionally, human activities, including changes in land use and land classification, have altered the natural flow of water, further reducing runoff. “This growing population, combined with decreasing runoff, presents a critical challenge for the future, which arguably makes it even more crucial to examine future projections from ESMs (Earth System Models) to anticipate further changes in runoff and develop adaptive strategies”, the analysis states.

The analysis of the best available ESMs warns that by the turn of the next century, 850 million people will feel the effects of declining runoff from the world’s major rivers.

That is more than three times the number estimated by previous analysis of Earth system models, says Puja Das, a post-doctoral research fellow at AI for Climate and Sustainability within the Institute for Experiential AI at Northeastern University.

“What (Das) found is that some of the more skillful models seem to project the worst conditions in terms of the impact of water scarcity,” says Northeastern professor Auroop Ganguly, who served as co-author for a paper Das published recently.

Population estimates are important because they give policymakers an idea of what to expect in terms of the availability of food, water and energy, since river runoff recharges water supplies, enriches agricultural soil and generates hydropower, Das says.

Earth systems models are complex computer simulations of Earth’s processes, such as the atmosphere, oceans and human activity.

Her research shows that the five most skillful models project 40 per cent of the world’s 30 major rivers will exhibit decreased runoff by 2100, affecting a population 100 times the size of New York City, as opposed to earlier estimates of 260 million.

“We chose the 30 biggest river basins around the world, including the Amazon, Congo, Ganges, Brahmaputra and Nile rivers,” she says. “We were trying to see how the runoff in those river basins, or water availability in those river basins, are presented in climate models.”

“We know that climate models use different equations and parameterizations to estimate these variables. We are trying to see how good they are,” she says.

The researchers compared two generations of Coupled Modeling Intercomparison Projects, the CMIP5 and the more recent CMIP6, to see how they performed against historical projections of annual runoff from 1960 to 2005, according to an official statement.

The latter modeling system, the CMIP6, was more skillful and accurate, Das says. Applying it to the future, “we found that the more skillful models are finding a worse future scenario in terms of water availability.”

Das says the research is important for two communities: policymakers and water resources managers who use Earth systems model results for understanding impacts and informing adaptation, as well as natural scientists, data scientists and computational modelers who build the Earth systems models and analyze the results.