Parts of Asia face irreversible declines in freshwater storage

The Tibetan Plateau – known as the “water tower of Asia” – currently supplies freshwater for almost two billion people living downstream. A new study published in the journal Nature Climate Change has found that climate change may cause irreversible declines in freshwater storage in this region, leading 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 2060.

“The prognosis is not good,” said study senior author Michael Mann, a distinguished professor of Atmospheric Science at the Pennsylvania State University. “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 percent 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 used both ‘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, to provide a benchmark of observed terrestrial water storage (TWS) changes during the past two decades (2002-2020), and projections over the next four decades (2021-2060). 

“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,” Professor Mann said.

The results revealed that, in recent decades, climate change has led to severe depletion in TWS (- 15.8 gigatons per year) in certain areas of the Tibetan Plateau, and significant increases in others (5.6 gigatons per year), most likely due to the competing effects of glacial retreat, lake expansion, and degradation of seasonally frozen grounds. Under a moderate carbon emissions scenario, the entire Tibetan Plateau could experience a loss of about 230 gigatons by 2060. 

Excess water loss projections of the Amu Darya basin (which supplies water to Central Asia and Afghanistan), and the Indus basin (which supplies water to Northern India, Pakistan, and Kashmir) indicate a 119 percent and 79 percent decrease, respectively. 

“Our study provides insights into hydrologic processes affecting high-mountain freshwater supplies that serve large downstream Asian populations,” said study co-author Di Long, an associate professor of Hydrologic Engineering at Tsinghua University. “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.”

“Substantial reductions in carbon emissions over the next decade, as the U.S. 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,” concluded Professor Mann.

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By Andrei Ionescu, Earth.com Staff Writer