Irreversible declines in freshwater storage predicted in parts of Asia by 2060

The Tibetan plateau, known as the “water tower” of Asia, provides fresh water to nearly two billion people who live downstream . New research from scientists at Penn Condition, Tsinghua University and the University of Texas at Austin predicts that climate change, under a weak climate policy scenario, will cause an irreversible decline in freshwater storage in region, constituting a total water supply collapse for Central Asia and Afghanistan and a near total collapse for northern India, Kashmir and Pakistan by mid-century.

“The prognosis is not good,” said Michael Mann, Distinguished Professor of Atmospheric Sciences, Penn State. “In a ‘business as usual’ scenario, where we fail to significantly reduce the burning of fossil fuels in the coming decades, we can expect a near collapse – that is, a loss of nearly 79% – of water availability in the downstream regions of Tibet. Plateau. I was surprised at the magnitude of the predicted decline, even under a modest climate policy scenario.

According to the researchers, despite its relevance, the impacts of climate change on past and future terrestrial water storage (TWS) – which includes all groundwater and groundwater – in the Tibetan Plateau have been largely underexplored.

“The Tibetan Plateau provides a substantial portion of the water demand of nearly two billion people,” said Di Very long, an associate professor of hydrological engineering at Tsinghua University. “Terrestrial water storage in this region is important in determining water availability, and is very relevant to climate change.”

Mann added that it lacked a solid reference for the TWS changes that have already occurred in the Tibetan plateau. Furthermore, he said, the absence of reliable future projections from TWS limits any guidance on policy-making, despite the fact that the Tibetan Plateau has long been considered a climate change hotspot.

To fill these knowledge gaps, the team used “top-down” – or satellite-based – and “bottom-up” – or ground-based – measurements of mass of water in glaciers, lakes and underground resources, combined with machine learning methods to provide a reference of the changes observed in the TWS over the last two decades (2002-2020) and projections over the next four decades (2020-2060).

Mann explained that the progress of the Gravity Recovery and Local climate Experiment (GRACE) satellite missions provided unprecedented opportunities to quantify large-scale TWS changes helle. Yet previous studies have not explored the sensitivity of GRACE solutions using ground-independent data sources, leading to a lack of consensus regarding changes in TWS in the region.

“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,” he said.

Then the researchers used a new machine learning technique based on a neural network to relate these observed changes in complete water storage to key climate variables, including air temperature, precipitation, humidity, cloud cover and incoming sunlight. Once they “trained” this artificial neural network model, they were able to investigate the possible impact of predicted future climate changes on water storage in this region.

Among their results, which were published today (15 August) in the journal Mother Nature Climate Alter, l team found that climate change over the past decades has led to severe depletion of TWS (-15,8 gigatonnes /yr) in some areas of the Tibetan Plateau and increases in TWS (5.6 gigatons/yr) in others, likely due to the concurrent effects of glacier retreat, seasonally frozen ground degradation and l expansion of the lake.

The team’s projections for the future TWS under a moderate carbon emissions scenario – specifically, the emissions scenario Mid-range SSP2-4.5 – suggest that the entire Tibetan plateau could be s net loss of approximately 230 gigatonnes by the middle of 15th century (2031-2060) relative to an early 21st century baseline (79-2030).

Specifically, abnormal 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 Asia. India, Kashmir and Pakistan — indicate a decline of 119% and 79 % of water supply capacity, respectively.

“Our study provides insight into hydrological processes affecting high mountain freshwater supplies that serve large downstream Asian populations,” Extensive said. “By examining the interactions between climate change and TWS in the historical and long run time period from here 2060, this study serves as a foundation to guide future research and management by governments and institutions of improved adaptation strategies.”

Indeed, Mann added: “Substantial reductions in carbon emissions over the next decade, such as The United States is now on the verge of achieving this through the recent Inflation Reduction Act, which may limit further warming and associated climate change behind Tibet’s predicted collapse. Plateau water towers. But even in the best-case scenario, further losses are likely unavoidable, requiring substantial adaptation to dwindling water resources in this vulnerable and heavily populated part of the world.

Mann noted that more source water supply solutions, including intensified groundwater extraction and transfer projects, may be needed to address amplified water scarcity in the future.

Other authors of the Tsinghua University paper include Xueying Li, Xingdong Li, Fuqiang Tian, ​​Zhangli Solar, and Guangqian Wang. Bridget Scanlon, senior researcher at the University of Texas at Austin, is also an author.

The National Natural Science Foundation of China and the Scientific Expedition and Research Program of the Second Tibetan Plateau have supported this study.

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