Climate change will cause a collapse in the water supply in the Tibetan Plateau – which supplies fresh water to nearly two billion people – by mid-century, a study has shown.
A weak climate policy will lead to "irreversible declines" in freshwater storage in the area, scientists said.
It would lead to a total collapse of the water supply for central Asia and Afghanistan and a near-total collapse for northern India, Kashmir and Pakistan by the middle of the century.
Michael Mann, distinguished professor of atmospheric science at Penn State in the US, said: "The prognosis is not good.
"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% 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."
The researchers said that, until now, the impacts of climate change on past and future terrestrial water storage (TWS) – which include all the above and below-ground water in the Tibetan Plateau – have largely been under-explored.
Di Long, associate professor of hydrologic engineering at Tsinghua University in Bejing, said: "The Tibetan Plateau supplies a substantial portion of the water demand for almost two billion people.
"Terrestrial water storage across this region is crucial in determining water availability, and it is highly sensitive to climate change."
The team used 'top-down’ (satellite-based) and 'bottom-up' (ground-based) measurements of water mass in glaciers, lakes and below-ground sources, combined with machine-learning techniques.
They created a benchmark of observed TWS changes over the past two decades (2002-2020) and projections over the next four decades (2021-2060).
Mann explained that advances in Gravity Recovery and Climate Experiment (GRACE) satellite missions have provided unprecedented opportunities to quantify TWS changes at large scales.
He said: "Compared to previous studies, establishing consistency between top-down and bottom-up approaches is what gives us confidence in this study that we can accurately measure the declines in TWS that have already occurred in this critical region."
Next, the researchers 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.
"Our study provides insights into hydrologic processes affecting high-mountain freshwater supplies that serve large downstream Asian populations," Long said.
"By examining the interactions between climate change and the TWS in the historical period and future by 2060, 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."
Watch: Town hit by flash flooding just days after historic drought