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

Time series of reconstructed terrestrial water storage anomalies (TWSA) and TWSA estimated from GRACE JPL-M over the (a) Amu Darya and (b) Indus basins. The red line shows the GRACE observations, while the blue line shows the ensemble mean of the TWSA reconstructed from nine GCMs (Table S2). The shading represents the uncertainty range of ±1 standard deviation between the outputs of different GCMs. Credit: Penn State, Tsinghua University

The Tibetan Plateau, known as Asia’s “water tower”, provides fresh water to nearly 2 billion people who live downstream. New research by scientists from Penn State, 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 will not succeed in significantly reducing the consumption of fossil fuels in the coming decades, we can expect a near collapse, i.e. a nearly 100% loss of water availability in the downstream regions of the Tibetan Plateau. I was surprised at the magnitude of the predicted decline, even under a modest climate policy scenario.”

According to the researchers, despite its importance, 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 under-explored.

“The Tibetan Plateau provides a substantial part of the water demand of nearly 2 billion people,” said Di Long, an associate professor of hydrological engineering at Tsinghua University. “Terrestrial water storage in this region is crucial in determining water availability, and it is highly sensitive 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 water mass in glaciers, lakes and underground sources, combined with machine learning. techniques to provide a baseline of observed TWS changes over the past two decades (2002-2020) and projections over the next four decades (2021-2060).

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

Lakes, glaciers and major river basins of the Tibetan plateau. Endorheic basins are shown in light purple and exorheic basins in light yellow. Bar charts show changes in TWS (TWSC) for each basin (only basins with TWS trends ≥ 1.0 Gt/yr are shown) between 2002 and 2017, estimated from the GRACE JPL-M solution. The blue bars represent the mass gain in TWS, while the red bars represent the mass loss, and the size of the bars represents the magnitude of changes in TWS (Gt/year). Specific values ​​for changes in TWS are shown in each basin. Credit: Penn State, Tsinghua University

Mann explained that advances in the Gravity Recovery and Climate Experiment (GRACE) satellite missions have provided unprecedented opportunities to quantify large-scale TWS changes. 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 the 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. he declares.

Next, the researchers used a new neural network-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” this artificial neural network model, they were able to study the likely impact of predicted future climate changes on water storage in this region.

Among their findings, published today (August 15) in the journal Natural climate changethe team found that climate change over the past decades has led to severe depletion of TWS (-15.8 gigatonnes/year) in some areas of the Tibetan Plateau and substantial increases in TWS (5.6 gigatonnes/ yr) in others, probably due to the competing effects of retreating glaciers, degradation of seasonally frozen soils, and expanding lakes.

The team’s projections for the future TWS under a moderate carbon emissions scenario, particularly the mid-range SSP2-4.5 emissions scenario, suggest that the entire Tibetan Plateau could incur a net loss of about 230 gigatons by the mid-21st century (2031‒2060) relative to an early 21st-century baseline (2002‒2030).

Specifically, the 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 – show a 119% and 79% drop in water consumption. supply capacity, respectively.

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

Projected changes in TWS and associated climatic factors over the TP through the mid-21st century under SSP2-4.5. (a‒c) Spatial patterns of linear trends for TWS reconstructed by DNN on the TP over the (a) past two decades (2002‒2020), (b) the next decade (2021‒2030) and (c) the mid-21st century (2031‒2060). The dotted line in (a) and (b) marks regions that have a significant trend (Mann-Kendall test at 5% level of significance). (d‒g) The difference between the 30-year average state for the period 2031‒2060 compared to the average for the period 2002‒2021 in (d) reconstructed TWS, (e) annual precipitation, (f) average temperature annual, and (g) solar radiation. All results were estimated from the ensemble average of nine GCMs under the mid-range SSP2-4.5 scenario. Credit: Penn State, Tsinghua University

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

Indeed, Mann added, “Substantial reductions in carbon emissions over the next decade, as the United States is now on the verge of achieving through the recent Cut Inflation Act, can limit additional warming and associated climate change behind the projected collapse of Tibet Plateau water towers But even in the best-case scenario, further losses are likely unavoidable, requiring substantial adaptation to dwindling resources water supply in this vulnerable and densely populated region of the world.

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

Observational and modeling data help to better understand the third pole

More information:
Di Long, Climate change threatens terrestrial water storage on the Tibetan Plateau, Natural climate change (2022). DOI: 10.1038/s41558-022-01443-0.

Provided by Pennsylvania State University

Quote: Irreversible freshwater storage declines projected in parts of Asia by 2060 (2022, August 15) Retrieved August 16, 2022 from -freshwater-storage-asia.html

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