Nearly two billion face irreversible decline in Asian freshwater storage

Scientists at Penn State, Tsinghua University and the University of Texas at Austin project that under a scenario of weak climate policy, the Tibetan Plateau, known as the Asia's 'water tower', would face severely depleted supplies.

The area supplies freshwater for nearly two billion people who live in regions downstream, including central Asia and Afghanistan as well as Northern India, Kashmir and Pakistan.

“The prognosis is not good,” said Michael Mann, professor of atmospheric science at Penn State.

“In a ‘business as usual’ scenario, where we fail to meaningfully curtail fossil-fuel burning in the decades ahead, we can expect a near collapse — that is, nearly 100 per cent loss — of water availability to downstream regions of the Tibetan Plateau. I was surprised at just how large the predicted decrease is even under a scenario of modest climate policy.”

To understand the area’s future terrestrial water storage, the team used satellite-based and ground-based measurements of water mass in glaciers, lakes and below-ground sources, combined with machine-learning techniques to provide a benchmark of observed changes over the past two decades (2002‒2020) and projections over the next four decades (2021–2060).

They used a novel neural-net-based machine-learning technique to relate these observed changes in total water storage to key climate variables, including air temperature, precipitation, humidity, cloud cover and incoming sunlight.

Once they ‘trained’ the model, they were able to look at how projected future changes in climate are likely to impact water storage in this region.

It was found that climate change in recent decades has already led to severe water depletion in in certain areas of the Tibetan Plateau, but substantial increases in others, likely due to the competing effects of glacier retreat, degradation of seasonally frozen ground, and lake expansion.

Under a moderate carbon-emissions scenario, the findings suggest that the entire Tibetan Plateau could experience a net loss of about 230 gigatons of water by the mid-21^st century (2031‒2060) relative to an early 21^st century (2002‒2030) baseline.

More specifically, excess water-loss projections for the Amu Darya basin — which supplies water to central Asia and Afghanistan — and the Indus basin — which supplies water to Northern India, Kashmir and Pakistan — indicate a decline of 119 per cent and 79 per cent in water-supply capacity, respectively.

Di Long, associate professor of hydrologic engineering at Tsinghua University, said: “This study serves as a basis to guide future research and the management by governments and institutions of improved adaptation strategies.”

Mann added: “Substantial reductions in carbon emissions over the next decade, as the US is now on the verge of achieving thanks to the recent Inflation Reduction Act, can limit the additional warming and associated climate changes behind the predicted collapse of the Tibetan Plateau water towers.

“But even in a best-case scenario, further losses are likely unavoidable, which will require substantial adaptation to decreasing water resources in this vulnerable, highly populated region of the world.”